Interfacial Structures and Properties of Organic Materials for Biosensors: An Overview
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paper_title: Oleophobic monolayers: I. Films adsorbed from solution in non-polar liquids☆

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It was found that certain types of polar organic molecules are adsorbed from solutions in non-polar solvents to form well-oriented monolayers on polished solid surfaces. Such monolayers imparted both hydrophobic and oleophobic properties to the polished surfaces of a variety of metallic and non-metallic solids and could be formed from a large variety of solvents, those used ranging from hydrocarbons like hexadecane, mineral oils, benzene, methylnaphthalene and dicyclohexyl to other solvents such as carbon disulfide, carbon tetrachloride, bromobenzene and diphenyloxide. ::: ::: It is shown that the mechanism of the formation of these films on platinum was reversible adsorption from solution and that it definitely was not the accumulation of insoluble films floating at the liquid-air interface as in the Langmuir-Blodgett method. It is concluded that the adsorbed films were made up of almost vertically oriented molecules which were nearly close-packed and attached to the surface through a surface active or polar group. Attention is called to the possibility that such films do not conform to the shape of the solid surface but might bridge over those surface depressions whose areas are not too great compared to the cross-sectional area of the molecules. ::: ::: In order that a compound be able to adsorb as an oleophobic monolayer it appears necessary that its molecular structure be in keeping with the following requirements. First, the molecules of the compound must be capable of approximating close-packed orientation in a monolayer. Second, the surface active or polar group must be located at one extremity of the molecule and one or more methyl groups must be located at the opposite extremity. Finally, the molecules must adsorb to a fiat solid surface with sufficient close-packing so that the outermost portion of the film is essentially a plane surface, densely populated with methyl groups. ::: ::: It was found that compounds whose molecular configurations resemble a long rod or a flat plate, with a polar group attached to one end of the rod or rim of the plate and one or more methyl groups at the opposite end of the rod or rim of the plate, readily satisfy these requirements. Exceptions were found in the case of aliphatic, unbranched polar molecules containing one or more unsaturated bonds, for these did not form oleophobic films. It is suggested that such molecules adsorb on solids at both the polar end group and the unsaturated bonds so that, instead of orienting with their axes vertical to the surface, they are arranged more nearly horizontally. ::: ::: Observations were made to determine the smallest concentrations of each of the various types of oleophobic compounds which would permit the formation of oleophobic monolayers on platinum and pyrex. While weight concentrations of only 10−7 were required for primary aliphatic amines and monocarboxylic acids, roughly 1000 times more was needed for the aliphatic alcohols, esters and ketones and for cholesterol. ::: ::: Some of the relations of these findings to past theoretical and applied research are discussed.
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paper_title: Electrochemical biosensor based on supported planar lipid bilayers for fast detection of pathogenic bacteria

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This paper presents a new ion-channel biosensor based on supported bilayer lipid membrane for direct and fast detection of Campylobacter species. The sensing element of a biosensor is composed of a stainless-steel working electrode, which is covered by artificial bilayer lipid membrane (BLM). Antibodies to bacteria embedded into the BLM are used as channel forming proteins. The biosensor has a strong signal amplification effect, which is defined as the total number of ions transported across the BLM. The total number of (univalent) ions flowing through the channels is 1010 ions s−1. The biosensor showed a very good sensitivity and selectivity to Campylobacter species.
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paper_title: Electrochemical impedance spectroscopy as a platform for reagentless bioaffinity sensing

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Abstract Simple reagentless immunosensor formats have been difficult to achieve, particularly for electrochemical devices, since antigen/hapten recognition by an antibody does not directly lead to a reaction cascade. A direct reading electrochemical immunosensor would have major advantages with respect to speed, de-skilled analysis and the development of multi-analyte sensors. Electrically conducting polymers, such as poly(pyrrole), allow for the intimate association between a biological recognition element and a potential reporter polymeric chain. We have polymerised poly(pyrrole), loaded with avidin or antibody to luteinising hormone (LH), on gold interdigitated electrodes (IDE) and employed two-electrode electrochemical impedance spectroscopy (EIS) to “visualise” charge transfer through the polymer as the basis for a reagentless protocol. We investigated bulk redox processes in the poly(pyrrole) films by cyclic voltammetry in order to ascertain the redox state of the film prior to EIS. The redox process of the immobilised protein molecule was identified and allowed the focusing of the EIS studies on polymer associated with the immobilised bioaffinity molecule. The polymer displayed both polaronic and electronic charge transfer during EIS studies. A possible binding-dependent response, observed as a decrease in peak polaronic phase angle, occurred when a redox cycle was performed on the film following exposure to the appropriate analyte. The response of poly(pyrrole) films loaded with avidin to d -biotin and two derivatives was assessed, which was shown to be sensitive to electrode pre-treatment. Poly(pyrrole) films loaded with antibody to LH allowed a calibration for LH to be constructed between 1 and 800 IU/l. Importantly, the films were responsive to LH within the clinically relevant range of 1–10 IU/l.
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paper_title: An optical biosensor using a fluorescent, swelling sensing element

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Abstract An optical sensor based on coupling the swelling of a polymer gel to a change in fluorescence intensity is discussed. A fluorophore, an amine functional group and the enzyme glucose oxidase were each incorporated into a crosslinked polymer gel, which was formed on the end of a fibre optic rod. While the amount of fluorophore remains constant, the gel volume changes in response to a change in the ionization state of the amine moiety. This change is related to glucose concentration. These effects were examined along with subsequent changes in the fluorescence of the gel.
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paper_title: Transducer aspects of biosensors

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Abstract A biosensor is a device which converts biological activity into a quantifiable signal. The basic principles, operation and applications of some typical electrochemical, piezo-electric and optical devices are reviewed. These sensors promise to provide an analytically powerful and inexpensive alternative to conventional technologies by enabling the identification of target substances in the presence of a number of interfering species. In the extreme cases where this is not possible, an integrated micro-separation and detection system on a silicon wafer is proposed. Finally, a summary of future markets and prospects for the developing technology of biosensing is given, with particular reference to growth opportunities in the healthcare sector.
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paper_title: Nanowire labeled direct-charge transfer biosensor for detecting Bacillus species.

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A direct-charge transfer (DCT) biosensor was developed for the detection of the foodborne pathogen, Bacillus cereus. The biosensor was fabricated using antibodies as the sensing element and polyaniline nanowire as the molecular electrical transducer. The sensor design consisted of four membrane pads, namely, sample application, conjugate, capture and absorption pads. Two sets of polyclonal antibodies, secondary antibodies conjugated with polyaniline nanowires and capture antibodies were applied to the conjugate and the capture pads of the biosensor, respectively. The detection technique was based on capillary flow action which allowed the liquid sample to move from one membrane to another. The working principle involved antigen-antibody interaction and direct electron charge flow to generate a resistance signal that was being recorded. Detection from sample application to final results was completed in 6 min in a reagentless process. Experiments were conducted to find the best performance of the biosensors by varying polyaniline types and concentrations. Polyaniline protonated with hydrochloric acid, emeraldine salt and polyaniline protonated with perchloric acid were the three kinds of polyaniline used in this study. The biosensor sensitivity in pure cultures of B. cereus was found to be 10(1) to 10(2)CFU/ml. Results indicated that using emeraldine salt at a concentration of 0.25 g/ml gave the best biosensor performance in terms of sensitivity. The biosensor was also found to be specific in detecting the presence of B. cereus in a mixed culture of different Bacillus species and other foodborne pathogens. The speed, sensitivity and ease-of-use of this biosensor make it a promising device for rapid field-based diagnosis towards the protection of our food supply chain. The phenotypic and genotypic similarities between B. cereus and Bacillus anthracis will also allow this biosensor to serve as an excellent model for the detection of B. anthracis.
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paper_title: Fibroblast cells: a sensing bioelement for glucose detection by impedance spectroscopy.

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Modifying the electrical properties of fibroblasts against various glucose concentrations can serve as a basis for a new, original sensing device. The aim of the present study is to test a new biosensor based on impedancemetry measurement using eukaryote cells. Fibroblast cells were grown on a small optically transparent indium tin oxide semiconductor electrode. Electrochemical impedance spectroscopy (EIS) was used to measure the effect of D-glucose on the electrical properties of fibroblast cells. Further analyses of the EIS results were performed using equivalent circuits in order to model the electrical flow through the interface. The linear calibration curve was established in the range 0-14 mM. The specification of the biosensors was verified using cytochalasin B as an inhibitor agent of the glucose transporters. The nonreactivity to sugars other than glucose was demonstrated. Such a biosensor could be applied to a more fundamental study of cell metabolism.
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paper_title: Impedance Spectroscopy: A Powerful Tool for Rapid Biomolecular Screening and Cell Culture Monitoring

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Dielectric spectroscopy or Electrochemical impedance spectroscopy (EIS) is traditionally used in corrosion monitoring, coatings evaluation, batteries, and electrodeposition and semiconductor characterization. However, in recent years, it is gaining widespread application in biotechnology, tissue engineering, and characterization of biological cells, disease diagnosis and cell culture monitoring. This article discusses the principles and implementation of dielectric spectroscopy in these bioanalytical applications. It provides examples of EIS as label-free, mediator-free strategies for rapid screening of biocompatible surfaces, monitoring pathogenic bacteria, as well as the analysis of heterogeneous systems, especially biological cells and tissues. Descriptions are given of the application of nanoparticles to improve the analytical sensitivities in EIS. Specific examples are given of the detection of base pair mismatches in the DNA sequence of Hepatitis B disease, TaySach's disease and Microcystis spp. Others include the EIS detection of viable pathogenic bacteria and the influence of nanomaterials in enhancing biosensor performance. Expanding applications in tissue engineering such as adsorption of proteins onto thiolated hexa(ethylene glycol)-terminated (EG6) self-assembled monolayer (SAM) are discussed.
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paper_title: Glucose biosensors based on organic light-emitting devices structurally integrated with a luminescent sensing element

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A platform for photoluminescence (PL) based biosensing is demonstrated for glucose. The sensor is structurally integrated, i.e., individually addressable organic light-emitting device (OLED) pixels (serving as the light source) and the sensing element are fabricated on glass or plastic substrates attached back-to-back. This results in a very compact, potentially miniaturizable sensor, which should strongly impact PL-based biosensor technology. The sensing element is an oxygen-sensitive dye coembedded with glucose oxidase in a thin film or dissolved in solution. The glucose biosensor is demonstrated for two OLED∕dye pairs: [blue OLED]∕[Ru dye] and [green OLED]∕[Pt dye]. Both PL-intensity and PL-lifetime modes are demonstrated for each pair; the lifetime mode eliminates the need for frequent sensor calibration. The sensor performance is evaluated in terms of design, dynamic range, limit of detection, and stability. The use of the glucose biosensor in conjunction with an oxygen sensor is also discussed.
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paper_title: Aptamer biosensor for label-free impedance spectroscopy detection of proteins based on recognition-induced switching of the surface charge.

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The recognition of proteins by aptamer-modified electrode transducers reverses the surface charge and leads to a novel label-free impedance spectroscopy bioelectronic detection protocol based on a decrease in the electron transfer resistance.
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paper_title: Fibre-optic biosensor based on luminescence and immobilized enzymes: Microdetermination of sorbitol, ethanol and oxaloacetate

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We have investigated highly selective and ultrasensitive biosensors based on luminescent enzyme systems linked to optical transducers. A fibre-optic sensor with immobilized enzymes was designed; the solid-phase bioreagent was maintained in close contact contact with the tip of a glass fibre bundle connected to the photomultiplier tube of a luminometer. A bacterial luminescence fibre-optic sensor was used for the microdetermination of NADH. Various NAD(P)-dependent enzymes, sorbitol dehydrogenase, alcohol dehydrogenase and malate dehydrogenase, were co-immobilized on preactivated polyamide membranes with the bacterial system and used for the microdetermination of sorbitol, ethanol and oxaloacetate at the nanomolar level with a good precision.
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paper_title: A high sensitivity amperometric biosensor using laccase as biorecognition element.

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An amperometric flow biosensor, using laccase from Rigidoporus lignosus as bioelement was developed. The laccase was kinetically characterized towards various phenolics both in solution and immobilized to a hydrophilic matrix by carbodiimide chemistry. A bioreactor connected to an amperometric flow cell by a FIA system was filled with the immobilized enzyme and the operational conditions of this biosensor were optimized as regards pH. Under the adopted experimental conditions, the immobilized enzyme oxidizes all the substrate molecules avoiding the need of cumbersome calibration procedures. The biosensor sensitivity, which was found to be 100 nA/μM for some of the tested substrates, resulted to be constant for more than 100 working days. This biosensor permits the detection of phenolics in aqueous solutions at concentrations in the nanomolar range and was successfully used to detect phenolics in wastewaters from olive oil mill without sample preparation.
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paper_title: Acoustic wave biosensors

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Abstract Acoustic waves excited in a piezoelectric medium provide an attractive technology for realizing a family of biosensors that are sensitive, portable, cheap and small. In this paper a wide range of bulk and surface-generated acoustic waves are described and prototype sensing-element geometries are presented. Results obtained using several candidate acoustic wave biosensors are also discussed.
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paper_title: Microbial biosensor array with transport mutants of Escherichia coli K12 for the simultaneous determination of mono-and disaccharides.

paper_content:

An automated flow-injection system with an integrated biosensor array using bacterial cells for the selective and simultaneous determination various mono- and disaccharides is described. The selectivity of the individually addressable sensors of the array was achieved by the combination of the metabolic response, measured as the O(2) consumption, of bacterial mutants of Escherichia coli K12 lacking different transport systems for individual carbohydrates. Kappa-carrageenan was used as immobilization matrix for entrapment of the bacterial cells in front of 6 individually addressable working electrodes of a screen-printed sensor array. The local consumption of molecular oxygen caused by the metabolic activity of the immobilized cells was amperometrically determined at the underlying screen-printed gold electrodes at a working potential of -600 mV vs. Ag/AgCl. Addition of mono- or disaccharides for which functional transport systems exist in the used transport mutant strains of E. coli K12 leads to an enhanced metabolic activity of the immobilized bacterial cells and to a concomitant depletion of oxygen at the electrode. Parallel determination of fructose, glucose, and sucrose was performed demonstrating the high selectivity of the proposed analytical system.
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paper_title: Detection of a Biomarker for Alzheimer's Disease from Synthetic and Clinical Samples Using a Nanoscale Optical Biosensor

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A nanoscale optical biosensor based on localized surface plasmon resonance (LSPR) spectroscopy has been developed to monitor the interaction between the antigen, amyloid-β derived diffusible ligands (ADDLs), and specific anti-ADDL antibodies. Using the sandwich assay format, this nanosensor provides quantitative binding information for both antigen and second antibody detection that permits the determination of ADDL concentration and offers the unique analysis of the aggregation mechanisms of this putative Alzheimer's disease pathogen at physiologically relevant monomer concentrations. Monitoring the LSPR-induced shifts from both ADDLs and a second polyclonal anti-ADDL antibody as a function of ADDL concentration reveals two ADDL epitopes that have binding constants to the specific anti-ADDL antibodies of 7.3 × 1012 M-1 and 9.5 × 108 M-1. The analysis of human brain extract and cerebrospinal fluid samples from control and Alzheimer's disease patients reveals that the LSPR nanosensor provides new informati...
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paper_title: Interdigitated array microelectrodes based impedance biosensors for detection of bacterial cells.

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Impedance spectroscopy is a sensitive technique to characterize the chemical and physical properties of solid, liquid, and gas phase materials. In recent years this technique has gained widespread use in developing biosensors for monitoring the catalyzed reaction of enzymes; the bio-molecular recognition events of specific proteins, nucleic acids, whole cells, antibodies or antibody-related substances; growth of bacterial cells; or the presence of bacterial cells in the aqueous medium. Interdigitated array microelectrodes (IDAM) have been integrated with impedance detection in order to miniaturize the conventional electrodes, enhance the sensitivity, and use the flexibility of electrode fabrication to suit the conventional electrochemical cell format or microfluidic devices for variety of applications in chemistry and life sciences. This article limits its discussion to IDAM based impedance biosensors for their applications in the detection of bacterial cells. It elaborates on different IDAM geometries their fabrication materials and design parameters, and types of detection techniques. Additionally, the shortcomings of the current techniques and some upcoming trends in this area are also mentioned.
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paper_title: Adapting selected nucleic acid ligands (aptamers) to biosensors.

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A flexible biosensor has been developed that utilizes immobilized nucleic acid aptamers to specifically detect free nonlabeled non-nucleic acid targets such as proteins. In a model system, an anti-thrombin DNA aptamer was fluorescently labeled and covalently attached to a glass support. Thrombin in solution was selectively detected by following changes in the evanescent-wave-induced fluorescence anisotropy of the immobilized aptamer. The new biosensor can detect as little as 0.7 amol of thrombin in a 140-pL interrogated volume, has a dynamic range of 3 orders of magnitude, has an inter-sensing-element measurement precision of better than 4% RSD over the range 0-200 nM, and requires less than 10 min for sample analysis. The aptamer-sensor format is generalizable and should allow sensitive, selective, and fast determination of a wide range of analytes.
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paper_title: Theory of elasticity

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A walking beam pumping unit is provided for pumping liquid from wells having gas pressure therein. The unit is driven by gas pressure from the well reciprocating the piston of a pneumatic cylinder up and down to swing the walking beam correspondingly and pump the liquid from the well. Gas under pressure is directed from the wellhead through a two-way valve to the opposite ends of the hydraulic cylinder in alternating fashion, so the piston has power strokes in opposite directions. Each power stroke, besides moving the walking beam, serves to recompress the gas used for the preceding power stroke sufficiently to inject it into the sales line. The setting of the two-way valve is controlled by a pneumatic actuator supplied with gas under pressure from the wellhead and having a thimble valve responsive to the up and down movement of the walking beam by means of adjustable stops carried thereon. The horsehead is counter-balanced by weights or by a pneumatic cylinder attached to the horsehead and actuated by movement thereof to provide counter-balancing gas pressure. In one form of the invention, the counter-balancing gas pressure is stored in a hollow skid assembly.
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paper_title: A magnetoelastic bioaffinity-based sensor for avidin.

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Abstract A magnetoelastic bioaffinity sensor coupled with biocatalytic precipitation is described for avidin detection. The non-specific adsorption characteristics of streptavidin on different functionalized sensor surfaces are examined. It is found that a biotinylated poly(ethylene glycol) (PEG) interface can effectively block non-specific adsorption of proteins. Coupled with the PEG immobilized sensor surface, alkaline phosphatase (AP) labeled streptavidin is used to track specific binding on the sensor. This mass-change-based signal is amplified by the accumulation on the sensor of insoluble products of 5-bromo-4-chloro-3-indolyl phosphate catalyzed by AP. The resulting mass loading on the sensor surface in turn shifts the resonance frequency of the magnetoelastic sensors, with an avidin detection limit of approximately 200 ng/ml.
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paper_title: Fibroblast cells: a sensing bioelement for glucose detection by impedance spectroscopy.

paper_content:

Modifying the electrical properties of fibroblasts against various glucose concentrations can serve as a basis for a new, original sensing device. The aim of the present study is to test a new biosensor based on impedancemetry measurement using eukaryote cells. Fibroblast cells were grown on a small optically transparent indium tin oxide semiconductor electrode. Electrochemical impedance spectroscopy (EIS) was used to measure the effect of D-glucose on the electrical properties of fibroblast cells. Further analyses of the EIS results were performed using equivalent circuits in order to model the electrical flow through the interface. The linear calibration curve was established in the range 0-14 mM. The specification of the biosensors was verified using cytochalasin B as an inhibitor agent of the glucose transporters. The nonreactivity to sugars other than glucose was demonstrated. Such a biosensor could be applied to a more fundamental study of cell metabolism.
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paper_title: Acoustic sensors based on surface-localized HPSWs for measurements in liquids

paper_content:

Abstract Acoustic wave probes based on horizontally polarized shear waves (HPSWs) in quartz plates are presented. These probes can be applied as physical or chemical sensors for measurements in liquids and to characterize thin solid films mechanically. An appropriate and comprehensive simulation tool has been developed and is used to work out the specific advantages of the proposed probing system, to interpret the experimental data and to optimize the probing devices for special measurement purposes. The use of additional coatings of known consistency is introduced, which leads to an enhanced sensitivity and a reduction of cross-sensitivities, in particular for surface-localized HPSWs in quartz, which have not yet been the subject of sensor research. Theoretical and experimental results confirm the huge potential of HPSW devices for sensing applications in liquids.
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paper_title: A staphylococcal enterotoxin B magnetoelastic immunosensor.

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A magnetoelastic immunosensor for detection of staphylococcal enterotoxin B (SEB) is described. The magnetoelastic sensor is a newly developed mass/elasticity-based transducer of high sensitivity having a material cost of approximately $0.001/sensor. Affinity-purified rabbit anti-SEB antibody was covalently immobilized on magnetoelastic sensors, of dimensions 6 mm x 2 mm x 28 microm. The affinity reaction of biotin-avidin and biocatalytic precipitation are used to amplify antigen-antibody binding events on the sensor surface. Horseradish peroxidase (HRP) and alkaline phosphatase were examined as the labeled enzymes to induce biocatalytic precipitation. The alkaline phosphatase substrate, 5-bromo-4-chloro-3-indolyl phosphate (BCIP) produces a dimer, which binds tightly to the sensor surface, inducing a change in sensor resonance frequency. The biosensor demonstrates a linear shift in resonance frequency with staphylococcal enterotoxin B concentration between 0.5 and 5 ng/ml, with a detection limit of 0.5 ng/ml.
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paper_title: Theoretical comparison of sensitivities of acoustic shear wave modes for (bio)chemical sensing in liquids

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A theoretical comparison of the sensitivities of various acoustic shear wave modes applied in (bio)chemical sensing in a liquid environment is presented. The sensitivity which is defined as the relative change of oscillation frequency due to mass adsorption in a (bio)chemical interface is obtained from perturbation theory. It is shown that the application of a Love wave mode for chemical compound sensing in liquids is very promising because of its high sensitivity.
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paper_title: Mass sensitivity of two-layer shear horizontal plate wave sensors

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Abstract Velocity and mass sensitivity formulae in explicit form for shear-horizontal (SH) plate wave sensors are presented. The sensor geometry consists of an isotropic plate of thickness b and an isotropic thin layer of thickness h. The mass loading layer is assumed to be acoustically thin (h ≪ λ), where λ is the acoustic wavelength. The mass loading sensitivity, Smv, of the sensors used in velocity measurements decreases by a factor of (1−C2) for all the SH modes due to the effects of the elasticity of the mass loading layer, where C2 = Vs22/Vs12, Vs1 and Vs2 are the shear wave velocities of the two materials respectively. Because of the inertial effect of the mass loading layer, Smv decreases by a factor of (1 + ρ2h/ρ1b)−1 for the lowest order mode and by a factor of (1 + 2ρ2h/ρ1b)−1 for the other modes, where ρ1 and ρ2 are the density of the plate and the loaded mass layer, respectively. We also show that the relation Smv = (V/Vg)Smf is valid for the composite case, where Smf is the sensitivity formula for sensors configured in resonant frequency measurements, and V and Vg are the phase and group velocity of the SH plate modes respectively.
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paper_title: Acoustic wave biosensors

paper_content:

Abstract Acoustic waves excited in a piezoelectric medium provide an attractive technology for realizing a family of biosensors that are sensitive, portable, cheap and small. In this paper a wide range of bulk and surface-generated acoustic waves are described and prototype sensing-element geometries are presented. Results obtained using several candidate acoustic wave biosensors are also discussed.
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paper_title: Surface acoustic wave biosensors: a review

paper_content:

This review presents an overview of 20 years of worldwide development in the field of biosensors based on special types of surface acoustic wave (SAW) devices that permit the highly sensitive detection of biorelevant molecules in liquid media (such as water or aqueous buffer solutions). 1987 saw the first approaches, which used either horizontally polarized shear waves (HPSW) in a delay line configuration on lithium tantalate (LiTaO(3)) substrates or SAW resonator structures on quartz or LiTaO(3) with periodic mass gratings. The latter are termed "surface transverse waves" (STW), and they have comparatively low attenuation values when operated in liquids. Later Love wave devices were developed, which used a film resonance effect to significantly reduce attenuation. All of these sensor approaches were accompanied by the development of appropriate sensing films. First attempts used simple layers of adsorbed antibodies. Later approaches used various types of covalently bound layers, for example those utilizing intermediate hydrogel layers. Recent approaches involve SAW biosensor devices inserted into compact systems with integrated fluidics for sample handling. To achieve this, the SAW biosensors can be embedded into micromachined polymer housings. Combining these two features will extend the system to create versatile biosensor arrays for generic lab use or for diagnostic purposes.
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paper_title: Theory, Instrumentation and Applications of Magnetoelastic Resonance Sensors: A Review

paper_content:

Thick-film magnetoelastic sensors vibrate mechanically in response to a time varying magnetic excitation field. The mechanical vibrations of the magnetostrictive magnetoelastic material launch, in turn, a magnetic field by which the sensor can be monitored. Magnetic field telemetry enables contact-less, remote-query operation that has enabled many practical uses of the sensor platform. This paper builds upon a review paper we published in Sensors in 2002 (Grimes, C.A.; et al. Sensors 2002, 2, 294–313), presenting a comprehensive review on the theory, operating principles, instrumentation and key applications of magnetoelastic sensing technology.
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paper_title: Microbial biosensor array with transport mutants of Escherichia coli K12 for the simultaneous determination of mono-and disaccharides.

paper_content:

An automated flow-injection system with an integrated biosensor array using bacterial cells for the selective and simultaneous determination various mono- and disaccharides is described. The selectivity of the individually addressable sensors of the array was achieved by the combination of the metabolic response, measured as the O(2) consumption, of bacterial mutants of Escherichia coli K12 lacking different transport systems for individual carbohydrates. Kappa-carrageenan was used as immobilization matrix for entrapment of the bacterial cells in front of 6 individually addressable working electrodes of a screen-printed sensor array. The local consumption of molecular oxygen caused by the metabolic activity of the immobilized cells was amperometrically determined at the underlying screen-printed gold electrodes at a working potential of -600 mV vs. Ag/AgCl. Addition of mono- or disaccharides for which functional transport systems exist in the used transport mutant strains of E. coli K12 leads to an enhanced metabolic activity of the immobilized bacterial cells and to a concomitant depletion of oxygen at the electrode. Parallel determination of fructose, glucose, and sucrose was performed demonstrating the high selectivity of the proposed analytical system.
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paper_title: A remote query magnetostrictive viscosity sensor.

paper_content:

Magnetically soft, magnetostrictive metallic glass ribbons are used as in-situ remote query viscosity sensors. When immersed in a liquid, changes in the resonant frequency of the ribbon-like sensors are shown to correlate with the square root of the liquid viscosity and density product. An elastic wave model is presented that describes the sensor response as a function of the frictional forces acting upon the sensor surface.
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paper_title: A novel Love-plate acoustic sensor utilizing polymer overlayers

paper_content:

A Love-plate sensor, consisting of a surface skimming bulk wave (SSBW) device coated with a polymer layer, was found to increase the acoustic signal through coupling of the SSBW wave to a Love wave. Insertion loss, phase and frequency measurements were used to assess the optimum thickness of the polymer layer and the sensitivity of the device to mass-loading and viscous coupling.
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paper_title: Surface plasmon resonance for gas detection and biosensing

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Abstract Surface plasmon resonance is a new optical technique in the field of chemical sensing. Under proper conditions the reflectivity of a thin metal film is extremely sensitive to optical variations in the medium on one side of it. This is due to the fact that surface plasmons are sensitive probes of the boundary conditions. The effect can be utilized in many ways. A description of how it can be used for gas detection is given, together with results from exploratory experiments with relevance to biosensing.
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paper_title: Quantification of bacterial cells based on autofluorescence on a microfluidic platform.

paper_content:

Bacterial counts provide important information during the processes such as pathogen detection and hygiene inspection and these processes are critical for public health and food/pharmaceutical production. In this study, we demonstrate the quantification of the number of bacterial cells based on the autofluorescence from the cell lysate on a microfluidic chip. We tested three model pathogenic bacteria (Listeria monocytogenes F4244, Salmonella Enteritidis PT1 and Escherichia coli O157:H7 EDL 933). In the experiment, a plug of approximately 150 pL containing lysate from 240 to 4100 cells was injected into a microfluidic channel with downstream laser-induced fluorescence detection under electrophoresis conditions. We found that the autofluorescence intensity increased with the number of cells almost linearly for all three bacteria. The autofluorescence remained a single peak when the cell lysate contained a mixture of different bacterial species. We also demonstrate a simple microfluidic device that integrates entrapment and electrical lysis of bacterial cells with fluorescence detection. Such a device can carry out the quantification of bacterial cells based on lysate autofluorescence without off-chip procedures. This study offers a simple and fast solution to on-chip quantification of bacterial cells without labeling. We believe that the method can be extended to other bacterial species.
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paper_title: Evanescent sensing of biomolecules and cells

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A technique using the evanescent field of tapered fibers is developed for rapid, convenient, and accurate sensing of biomolecules and cells using small volumes of analytes in the range of 150 μl. A tapered optical fiber was fabricated by heat pulling with a flame. A simple fiber-mounting device was developed to accommodate the optical fiber and provide a reaction chamber for analytes to interact with the tapered region. Using an analytical grade spectrofluorometer nicotinamide adenine dinucleotide (NADH), nicotinamide adenine dinucleotide phosphate (NADPH), and Chinese Hamster Ovary (CHO) cells at various concentrations were measured. A parameter, namely, the product of extinction coefficient and light path, is used to characterize detection sensitivity. Results from biomolecules and cells show that the sensitivity of the tapered fiber is at least an order of magnitude higher than that obtained in a cuvette arrangement.
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paper_title: An Optical Biosensor for Rapid and Label-Free Detection of Cells

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We report a broadly applicable optical method for rapid and label-free detection of as few as 45 cells. In this method, bacterial cells are detected by measuring the amount of laser light transmitted through a small glass well functionalized with antibodies which specifically recognize and capture the cells. The described approach is simple, rapid, economical, and promising for portable and high-throughput detection of a wide variety of pathogenic and infectious cells.
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paper_title: Surface plasmon resonance on gratings as a novel means for gas sensing

paper_content:

Abstract A novel technique for sensing small changes in dielectric constant using the phenomenon of surface plasmon resonance has been developed. The principle of this technique is based on the measurement of a resonance maximum on a background of weak signal, giving improved signal-to-noise ratios over previously reported surface plasmon techniques. The sensing of the condensation of several organic vapours onto a silver surface is used to demonstrate the effectiveness of the technique. Its potential as a hand-held in-field gas sensor is discussed.
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paper_title: Label-free fiber optic biosensor based on evanescent wave absorbance at 280 nm

paper_content:

Abstract Several analytes of interest such as bacteria, virus and some of the clinically important proteins and marker molecules absorb light in the ultra violet region (UV). In this study, we have investigated the possibility to develop a label-free fiber optic biosensor based on evanescent wave absorbance (EWA) at 280 nm to detect the presence of such analytes. A light emitting diode (LED) in UV with peak emission at 280 nm and span of ±10 nm was chosen as a light source to limit the solarization of the fiber probes. Numerical simulations were performed to investigate the effect of fiber parameters and wavelength of operation on EWA and its sensitivity. Experimental verifications proved the validity of the simulations. The absorbance behavior of fiber sensor probes in the visible region was studied using FITC as absorbing molecule. Goat anti-human IgG (GaHIgG) was chosen as a model analyte. Human IgG immobilized fiber probes were subjected to goat anti-human IgG to test the absorbance response of the probes at 280 nm. These studies demonstrate that intrinsic absorbance properties of biomolecules may be utilized for development of absorbance based label-free biosensors. The sensitivity, which is a limiting factor, can be improved with better optics.
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paper_title: Optical chemical sensing employing surface plasmon resonance

paper_content:

An optical sensor based on the phenomenon of light-excited surface plasmon resonance has been investigated to measure liquid chemical concentrations. A white light source is used to excite surface plasmon waves at a metal/analyte interface. The wavelength of maximum absorption in the reflected light depends uniquely on the refractive index of the analyte.
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paper_title: Growth of Ultrasmooth Octadecyltrichlorosilane Self-Assembled Monolayers on SiO2

paper_content:

Ultrasmooth octadecyltrichlorosilane (OTS) monolayers (2.6 ± 0.2 nm thick, RMS roughness ∼1.0 A) can be obtained reproducibly by exposing clean native SiO2 surfaces to a dry solution of OTS in Isopar-G. A clean room is not required. Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), contact angle data, and ellipsometry show that film formation occurs through a “patch expansion” process and terminates once a single monolayer is formed, after about 2 days. These monolayers are suitable as substrates for high-resolution electron beam and AFM or STM lithography. Further observations highlight the importance of controlling water content during deposition of siloxane self-assembled monolayers. OTS covers the surface much faster when there is a little water in the OTS solution; contact angle and ellipsometry data indicate formation of a hydrophobic, 2.6 nm thick film after about 2 h. However, these OTS films have a totally different growth mechanism than films grown from dry solutions and are...
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paper_title: Easy and Efficient Bonding of Biomolecules to an Oxide Surface of Silicon

paper_content:

A new method is described to attach biological molecules to the surface of silicon. Semiconductors such as Si modified with surface-bound capture molecules have enormous potential for use in biosensors for which an ideal detection platform should be inexpensive, recognize targets rapidly with high sensitivity and specificity, and possess superior stability. In this process, a self-assembled film of an organophosphonic acid is bonded to the native or synthesized oxide-coated Si surface as a film of the corresponding phosphonate. The phosphonate film is functionalized to enable covalently coupling biological molecules, ranging in size from small peptides to large multi-subunit proteins, to the Si surface. Surface modification and biomolecule coupling procedures are easily accomplished: all reactions can proceed in air, and most take place under ambient conditions. The biomolecule-modified surfaces are stable under physiological conditions, are selective for adhesion of specific cells types, and are reusable.
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paper_title: Potassium ion-sensitive field effect transistor

paper_content:

The construction and theory of operation of a potassiumsensitive field effect transistor Is described, and Its performance is characterized both as a solid-state field-effect device and as an electrochemical sensor. The performance of this device is comparable with the correspondlng PVC-type ion selective electrodes. The transistor operates satisfactorliy in the presence of proteins and it has been used for determination of potassium ion concentration in blood serum. A new type of electrochemical sensor, an ion-sensitive field-effect transistor (ISFET), was introduced when Bergveld removed the metal gate from a metal oxide semiconductor field-effect transistor (MOSFET) and exposed the silicon oxide gate insulator to a measured solution (I). A similar approach was followed later by Matsuo and Wise (Z), and this new subject area has been recently reviewed by Zemel (3). In the broader sense of chemically sensitive field-effect transistors, one sensitive to molecular hydrogen has also been reported (4). The ISFET is a result of the integration of two technologies: ion-selective electrodes and solid state microelectronics. This development opens several new possibilities, such as miniaturization, development of multiprobes, all solidstate design and in situ signal processing. Because of its small size, it presents a difficult encapsulation and packaging problem which is, however, amply offset by the elimination of electrical pick-up noise by in situ impedance conversion and on site signal amplification. Bergveld did not modify the ion-sensitive layer in any way although he considered introducing impurities in order to render the device ion selective. In this paper, we introduce a class of devices having a chemically-sensitive layer placed over the gate region, and we report our results with valinomycin/plasticizer/poly(vinylchloride) membrane
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paper_title: Organic functionalization of group IV semiconductor surfaces: principles, examples, applications, and prospects

paper_content:

Organic functionalization is emerging as an important area in the development of new semiconductor-based materials and devices. Direct, covalent attachment of organic layers to a semiconductor interface provides for the incorporation of many new properties, including lubrication, optical response, chemical sensing, or biocompatibility. Methods by which to incorporate organic functionality to the surfaces of semiconductors have seen immense progress in recent years, and in this article several of these approaches are reviewed. Examples are included from both dry and wet processing environments. The focus of the article is on attachment strategies that demonstrate the molecular nature of the semiconductor surface. In many cases, the surfaces mimic the reactivity of their molecular carbon or organosilane counterparts, and examples of functionalization reactions are described in which direct analogies to textbook organic and inorganic chemistry can be applied. This article addresses the expected impact of these functionalization strategies on emerging technologies in nanotechnology, sensing, and bioengineering.
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paper_title: Enzyme monolayer-functionalized field-effect transistors for biosensor applications

paper_content:

Abstract A gate surface of an ion-selective field-effect transistor was modified with a monolayer enzyme array that stimulates biocatalytic reactions that control the gate potential. Stepwise assemblage of the biocatalytic layer included primary silanization of the Al 2 O 3 -gate with 3-aminopropyltriethoxysilane, subsequent activation of the amino groups with glutaric dialdehyde and the covalent attachment of the enzyme to the functionalized gate surface. Urease, glucose oxidase, acetylcholine esterase and α-chymotrypsin were used to organize the biocatalytic matrices onto the chip gate. The resulting enzyme-based field-effect transistors, ENFETs, demonstrated capability to sense urea, glucose, acetylcholine and N -acetyl- l -tyrosine ethyl ester, respectively. The mechanism of the biosensing involves the alteration of the pH in the sensing layer by the biocatalytic reactions and the detection of the pH change by the ENFET. The major advantage of the enzyme-thin-layered FET devices as biosensors is the fast response-time (several tens of seconds) of these bioelectronic devices. This advantage over traditional thick-polymer-based ENFETs results from the low diffusion barrier for the substrate penetration to the biocatalytic active sites and minute isolation of the pH-sensitive gate surface from the bulk solution.
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paper_title: Surface Characterization of a Silicon-Chip-Based DNA Microarray

paper_content:

The immobilization of DNA (deoxyribonucleic acid) on solid supports is a crucial step for any application in the field of DNA microarrays. It determines the efficacy of the hybridization and influences the signal strength for the detection. We used solid supports made from silicon wafers as an alternative substrate to the commonly used microscope glass slides. The covalent immobilization of thiol-terminated DNA oligonucleotides on self-assembled layers of (3-mercaptopropyl)trimethoxysilane (MPTS) by disulfide bond formation was investigated. Contact angle measurement, variable angle spectral ellipsometry (VASE), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) were used to characterize the changing properties of the surface during the DNA array fabrication. During wafer processing the contact angle changed from 3° for the hydroxylated surface to 48.5° after deposition of MPTS. XPS data demonstrated that all sulfur in the MPTS layer was present in the form of reduced SH or S−S grou...
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paper_title: The ion sensitive field effect transistor (ISFET) pH electrode: a new sensor for long term ambulatory pH monitoring.

paper_content:

Intraluminal pH monitoring in man should be performed with disposable multichannel assemblies that allow recordings at multiple sites and prevent transmission of infection. Currently available glass electrodes are unsuitable for this purpose because of their size and price. We have thus constructed and tested a small, combined ion sensitive field effect transistor (ISFET) pH electrode incorporating an integral reference electrode. In vitro studies showed that both ISFET and glass electrodes (440-M4, Ingold, Switzerland) have a linear response over the pH range 1.3-8.0 and that they are comparable with regard to response time and 24 hour drift. Twenty one hour intragastric pH recordings were performed simultaneously in eight healthy volunteers using a glass electrode and an ISFET electrode, placed no more than 2 mm apart in a combined assembly. This was located in the gastric corpus under fluoroscopic control. The 21 hour pH curves recorded by each electrode type showed identical patterns: an early morning rise in pH with three meal-associated pH peaks lasting for about two to three hours. The means of the 21 hour pH medians were 2.09 and 2.07 as measured by the glass and the ISFET electrodes respectively. Thus, ISFETs are suitable for the construction of inexpensive and hence disposable multichannel pH monitoring assemblies of small diameter. Provided that they can be produced in large numbers with appropriate technical support, ISFETs have the potential to replace glass electrodes for long term monitoring of gastrointestinal luminal acidity.
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paper_title: Integrated Micro Multi Ion Sensor Using Field Effect of Semiconductor

paper_content:

The fabrication of a microprobe for simultaneous, independent and in-vivo measurements of H+ and Na+ ion activities is described.
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paper_title: ELECTROCHEMICAL BIOSENSORS: RECOMMENDED DEFINITIONS AND CLASSIFICATION*

paper_content:

*A special report on the International Union of Pure and Applied Chemistry, Physical Chemistry Division, Commission I.7 (Biophysical Chemistry), Analytical Chemistry Division, Commission V.5 (Electroanalytical Chemistry).
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paper_title: Electrochemical biosensors - principles and applications

paper_content:

Summary The first scientifically proposed as well as successfully commercialized biosensors were those based on electrochemical sensors for multiple analytes. Electrochemical biosensors have been studied for a long time. Currently, transducers based on semiconductors and screen printed electrodes represent a typical platform for the construction of biosensors. Enzymes or enzyme labeled antibodies are the most common biorecognition components of biosensors. The principles of, and the most typical applications for electrochemical biosensors are described in this review. The relevant systems are divided into three types according to the operating principle governing their method of measurement: potentiometric, amperometric and impedimetric transducers, and the representative devices are described for each group. Some of the most typical assays are also mentioned in the text.
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paper_title: ELECTROCHEMICAL BIOSENSORS: RECOMMENDED DEFINITIONS AND CLASSIFICATION*

paper_content:

*A special report on the International Union of Pure and Applied Chemistry, Physical Chemistry Division, Commission I.7 (Biophysical Chemistry), Analytical Chemistry Division, Commission V.5 (Electroanalytical Chemistry).
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paper_title: Polymeric Sensors to Monitor Cockroach Locomotion

paper_content:

We have developed a method using a polyvinylidene fluoride (PVDF) polymeric sensor to monitor the leg movements of cockroaches. The PVDF sensor was coated with gold as electrodes. It was attached to the leg of a roach. The voltage signals generated through bending directly correlate to the movement of the legs. It was found that the output voltage was a function of the degree of sensor bending caused by the movement of leg sclerites. An ex situ motorized linear stage generated similar results.
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paper_title: Stress-resolved and cockroach-friendly piezoelectric sensors

paper_content:

We investigate effects of bending stress on piezoelectric properties of polyvinylidene fluoride (PVDF) as a polymer ::: sensor. The sensor was designed and fabricated into a special size and shape so that it can be attached to small ::: insects, such as the American cockroach (Periplaneta Americana) to measure the insects' locomotion. The ::: performance of the sensor is studied using a controlled linear stage to buckle the sensor mimicking the bending of ::: the sensor due to the leg movements of cockroaches. For comparison, a roach robot was used for multi-leg study. ::: Results indicate that buckling motion of the sensor produce an output that is different from regular stretching effect. ::: The sensor-generated charge depends on the localized stress distribution and dipole alignment. This paper discusses ::: the methods of characterization of piezoelectricity useful for insect applications.
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paper_title: Studying insect motion with piezoelectric sensors

paper_content:

Piezoelectric materials have been widely used in applications such as transducers, acoustic components, as well as ::: motion, pressure and airborne sensors. Because of the material's biocompatibility and flexibility, we have been able to ::: apply small piezoelectric sensors, made of PVDF, to cockroaches. We built a laboratory test system to study the ::: piezoelectric properties of a bending sensor. The tested motion was compared with that of the sensor attached to a ::: cockroach. Surface characterization and finite element analysis revealed the effects of microstructure on piezoelectric ::: response. The sensor attachment enables us to monitor the insects' locomotion and study their behaviors. The ::: applications of engineering materials to insects opens the door to innovating approaches to integrating biological, ::: mechanical and electrical systems.
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paper_title: The molecular level modification of surfaces: from self-assembled monolayers to complex molecular assemblies

paper_content:

The modification of surfaces with self-assembled monolayers (SAMs) containing multiple different molecules, or containing molecules with multiple different functional components, or both, has become increasingly popular over the last two decades. This explosion of interest is primarily related to the ability to control the modification of interfaces with something approaching molecular level control and to the ability to characterise the molecular constructs by which the surface is modified. Over this time the level of sophistication of molecular constructs, and the level of knowledge related to how to fabricate molecular constructs on surfaces have advanced enormously. This critical review aims to guide researchers interested in modifying surfaces with a high degree of control to the use of organic layers. Highlighted are some of the issues to consider when working with SAMs, as well as some of the lessons learnt (169 references).
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paper_title: Formation of monolayer films by the spontaneous assembly of organic thiols from solution onto gold

paper_content:

Abstract : Long-chain alkanethiols, HS(CH2)nX, adsorb from solution onto gold surfaces and form ordered, oriented monolayer films. The properties of the interfaces between the films and liquids are largely independent of chain length when n > 10; in particular, wetting is not directly influenced by the proximity of the underlying gold substrate. The specific interaction of gold with sulfur and other soft nucleophiles and its low reactivity toward most hard acids and bases make it possible to vary the structure of the terminal group, X, widely and thus permit the introduction of a great range of functional groups into a surface. Studies of wettability of these monolayers, and of their composition using X-ray photoelectron spectroscopy (XPS), indicate that the monolayers are oriented with the tail group, X, exposed at the monolayer-air or monolayer- liquid interface. The adsorption of simple n-alkanethiols generates hydrophobic surfaces whose free energy (19 mJ/sq. m) is the lowest of any hydrocarbon surface studied to date. Measurement of contact angles is a useful tool for studying the structure and chemistry of the outermost few angstroms of a surface. This work used contact angles and optical ellipsometry to study the kinetics of adsorption of monolayer films and to examine the experimental conditions necessary for the formation of high-quality films.
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paper_title: Mechanisms and kinetics of self-assembled monolayer formation.

paper_content:

Recent applications of various in situ techniques have dramatically improved our understanding of the self-organization process of adsorbed molecular monolayers on solid surfaces. The process involves several steps, starting with bulk solution transport and surface adsorption and continuing with the two-dimensional organization on the substrate of interest. This later process can involve passage through one or more intermediate surface phases and can often be described using two-dimensional nucleation and growth models. A rich picture has emerged that combines elements of surfactant adsorption at interfaces and epitaxial growth with the additional complication of long-chain molecules with many degrees of freedom.
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paper_title: Molecular-Level Approach To Inhibit Degradations of Alkanethiol Self-Assembled Monolayers in Aqueous Media

paper_content:

A molecular-level approach is developed to prevent or inhibit the degradation processes of alkanethiol self-assembled monolayers (SAMs). Previous studies revealed two degradation pathways: direct desorption and oxidation−desorption. By use of scanning tunneling microscopy (STM) and atomic force microscopy (AFM), in situ and time-dependent imaging reveals and confirms that degradations of alkanethiol SAMs on gold mainly initiate at defect sites, such as domain boundaries and vacancy islands, and then propagate into the ordered domains. Our approach targets at attaching small molecules with preferred adhesion to the defects. The best candidates are aqueous media containing a small amount of amphiphilic surfactant molecules, such as N,N-dimethylformamide (DMF) or dimethyl sulfoxide (DMSO). High-resolution studies demonstrate that DMSO and DMF molecules attach to SAM surfaces and more favorably at defect sites, forming relatively stable adsorbates. This attachment increases the activation energy sufficiently...
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paper_title: Electrochemical Modification of Glassy Carbon Electrode Using Aromatic Diazonium Salts. 1. Blocking Effect of 4-Nitrophenyl and 4-Carboxyphenyl Groups

paper_content:

The effect of a 4-carboxyphenyl or a 4-nitrophenyl thin film at the surface of a glassy carbon electrode on their electrochemical responses in the presence of various electroactive probes has been investigated. The grafting of a substituted phenyl group to a glassy carbon electrode was achieved by electrochemical reduction of the corresponding substituted phenyldiazonium derivative in acetonitrile. The blocking properties of the film depend primarily on electrostatic and electrolyte/solvent effects. Permselectivity for the 4-carboxyphenyl film can be achieved by controlling the dissociation of the carboxy group. The substituted phenyl layer is much more compact and less permeable in contact with a nonaqueous solvent than with an aqueous solvent presumably because the layer is poorly solvated. Electrochemical impedance measurements indicate that the kinetics of electron transfer are slowed down when the time used to modify the glassy carbon electrode is increased. Cyclic voltammetry and X-ray photoelectron...
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paper_title: Organometallic chemistry on silicon surfaces: formation of functional monolayers bound through Si–C bonds

paper_content:

Silicon chips form the backbone of modern computing and yet until recently, the surface chemistry of this technologically essential material has remained relatively unexplored. As the size of devices on silicon wafers shrink (towards gigascale integration), the surface characteristics play increasingly crucial roles in the proper functioning of the device since the ratio of surface atoms/bulk escalates. While surface oxide has served thus far as the main passivation route, there is strong interest in precisely tailoring the interface properties, not only for microelectronics, but other applications including sensors, MEMS and biologically active surfaces. As a result, organometallic and organic chemistry has become essential for the synthesis of functional, modifiable monolayers, bound to non-oxidized silicon surfaces through silicon–carbon bonds. The latest approaches towards preparation of monolayers through Si–C bonds on both flat and photoluminescent porous silicon are described. Wet chemical techniques, accessible to most organometallic/organic chemists are highlighted, but recent developments using UHV conditions also receive attention.
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paper_title: Thiol self-assembled monolayers on mercury surfaces: the adsorption and electrochemistry of ω-mercaptoalkanoic acids

paper_content:

Abstract The formation of self-assembled monolayers (SAMs) of ω-mercaptoalkanoic acids on a mercury surface under potential control has been studied. Cyclic voltammetry and AC voltammetry were used for investigating the different phases and transitions that the homologous series of these thiols form and undergo. We find that the thiols are either physisorbed or chemisorbed depending on the applied potential and the transition between these two states occurs through a Faradaic process. Moreover, the chemisorption of the thiols results in multilayer deposition when the thiol monolayer does not block electron transfer. Finally, the implications of this study to the formation and manipulation of SAMs of ω-functionalized alkanethiols on Hg are discussed.
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paper_title: Influence of Adsorbate Ordering on Rates of UV Photooxidation of Self-Assembled Monolayers

paper_content:

The photooxidation of a range of methyl terminated straight chain alkylthiol (CH3(CH2)n-1SH) self-assembled monolayers (SAMs) on Au has been investigated using X-ray photoelectron spectroscopy (XPS). The photooxidation process has been found to involve the oxidation of the thiolate group to a sulfonate by an active O2 species (possibly singlet oxygen). The rate of photooxidation was found to vary strongly with alkyl chain length and has been correlated with the amount of disorder within the monolayers. Short-chain SAMs (n ≤ 8) have the highest disorder and oxidize the fastest, with the rate of oxidation increasing sharply with decreasing n, while close packed long-chain SAMs (n ≥ 12) oxidize much more slowly, with the rate of oxidation decreasing slowly with increasing n.
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paper_title: Comparison of the structures and wetting properties of self-assembled monolayers of n-alkanethiols on the coinage metal surfaces, copper, silver, and gold

paper_content:

Long-chain alkanethiols, HS(CH2),CH3, adsorb from solution onto.the surfaces of gold, silver, and copper and form monolayers. Reflection infrared spectroscopy indicates that monolayers on silver and on copper (when carefully prepared) have the chains in well-defined molecular orientations and in crystalline-like phase states, as has been observed on gold. Monolayers on silver are structurally related to those formed by adsorption on gold, but different in details of orientation. The monolayers formed on copper are structurally more complex and show a pronounced sensitivity to the details of the sample preparation. Quantitative analysis of the IR data using numerical simulations based on an average single chain model suggests that the alkyl chains in monolayers on silver are all-trans zig-zag and canted by - 12' from the normal to the surface. The analysis also suggests a twist of the plane containing the carbon backbone of -45' from the plane defined by the tilt and surface normal vectors. For comparison, the monolayers that form on adsorption of alkanethiols on gold surfaces, as judged by their vibrational spectra, are also trans zig-zag extended but, when interpreted in the context of the same single chain model, have a cant angle of -27O and a twist of the plane of the carbon backbone of -53'. The monolayers formed on copper (when they are obtained in high quality) exhibit infrared spectra effectively indistinguishable from those on silver and thus appear to have the same structure. Films on copper are also commonly obtained that are structurally ill-defined and appear to contain significant densities of gauche conformations. These spectroscopically based interpretations are compatible with inferences from wetting and XPS measurements. The structure of the substrate-sulfur interface appears to control molecular orientations of the alkyl groups in these films. An improved structural model, incorporating a two-chain unit cell and allowing for the temperature-dependent population of gauche conformations, is presented and applied to the specific case of the structures formed on gold.
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paper_title: Synthesis, Structure, and Properties of Model Organic Surfaces

paper_content:

Interest in the properties of thin-film organic materials, especially regard­ ing organized monoand multilayer assemblies, has grown enormously in recent years. The impetus for this renaissance-the relevance of such structures and materials to biological interfaces and membranes, corrosion protection, electrochemistry, wetting, adhesion, and microelectronic cir­ cuit fabrication, for example-has been discussed extensively (1,2). Such materials are clearly contributing significantly to our more general under­ standing of the physics and chemistry of complex surfaces and interfaces. In this article, we provide a general overview of areas in which this has been persuasively demonstrated and, in so doing, suggest the intellectual issues that drive current research in this field. Until recently, there were no generally applicable methods to construct well-ordered, organic surface phases by using any rational synthetic scheme. Metal, semiconductor, and oxide surfaces can be easily prepared by orienting, cutting (or cleaving), and polishing single-crystal substrates followed by cleaning in ultrahigh vacuum (URV) (i.e. by ion bom-
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paper_title: Self-Assembled Monolayers of Alkanethiolates on Palladium Are Good Etch Resists

paper_content:

This paper describes microcontact printing (μCP) of long-chain alkanethiolates on palladium, followed by solution-phase etching with an iron(III)-based etchant, to make patterned structures. The commonly used soft-lithographic procedure for fabricating microstructuresμCP of SAMs on goldhas three shortcomings: a significant surface density of pinhole defects, substantial edge roughness, and incompatibility with processes used in CMOS fabrication. Microcontact printing on palladium gives fewer defects and smaller edge roughness than on gold, and is compatible with CMOS. The mechanism by which etch-resistant patterns are formed is different for palladium and gold. The Pd/S interfacial layer formed by the reaction of palladium films with sulfur-containing compounds provides good resistance to etches independently of the barrier to access the surface provided by the film of (CH2)n groups in the long-chain SAMs. This barrier is the basis of the etch resistance of SAMs on gold, but only supplements the etch res...
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paper_title: Control of carrier density by self-assembled monolayers in organic field-effect transistors

paper_content:

Control of carrier density by self-assembled monolayers in organic field-effect transistors
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paper_title: Infrared characterization of interfacial Si-O bond formation on silanized flat SiO2/Si surfaces.

paper_content:

Chemical functionalization of silicon oxide (SiO(2)) surfaces with silane molecules is an important technique for a variety of device and sensor applications. Quality control of self-assembled monolayers (SAMs) is difficult to achieve because of the lack of a direct measure for newly formed interfacial Si-O bonds. Herein we report a sensitive measure of the bonding interface between the SAM and SiO(2), whereby the longitudinal optical (LO) phonon mode of SiO(2) provides a high level of selectivity for the characterization of newly formed interfacial bonds. The intensity and spectral position of the LO peak, observed upon silanization of a variety of silane molecules, are shown to be reliable fingerprints of formation of interfacial bonds that effectively extend the Si-O network after SAM formation. While the IR absorption intensities of functional groups (e.g., >C=O, CH(2)/CH(3)) depend on the nature of the films, the blue-shift and intensity increase of the LO phonon mode are common to all silane molecules investigated and their magnitude is associated with the creation of interfacial bonds only. Moreover, results from this study demonstrate the ability of the LO phonon mode to analyze the silanization kinetics of SiO(2) surfaces, which provides mechanistic insights on the self-assembly process to help achieve a stable and high quality SAM.
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paper_title: The molecular level modification of surfaces: from self-assembled monolayers to complex molecular assemblies

paper_content:

The modification of surfaces with self-assembled monolayers (SAMs) containing multiple different molecules, or containing molecules with multiple different functional components, or both, has become increasingly popular over the last two decades. This explosion of interest is primarily related to the ability to control the modification of interfaces with something approaching molecular level control and to the ability to characterise the molecular constructs by which the surface is modified. Over this time the level of sophistication of molecular constructs, and the level of knowledge related to how to fabricate molecular constructs on surfaces have advanced enormously. This critical review aims to guide researchers interested in modifying surfaces with a high degree of control to the use of organic layers. Highlighted are some of the issues to consider when working with SAMs, as well as some of the lessons learnt (169 references).
---
paper_title: Organometallic chemistry on silicon surfaces: formation of functional monolayers bound through Si–C bonds

paper_content:

Silicon chips form the backbone of modern computing and yet until recently, the surface chemistry of this technologically essential material has remained relatively unexplored. As the size of devices on silicon wafers shrink (towards gigascale integration), the surface characteristics play increasingly crucial roles in the proper functioning of the device since the ratio of surface atoms/bulk escalates. While surface oxide has served thus far as the main passivation route, there is strong interest in precisely tailoring the interface properties, not only for microelectronics, but other applications including sensors, MEMS and biologically active surfaces. As a result, organometallic and organic chemistry has become essential for the synthesis of functional, modifiable monolayers, bound to non-oxidized silicon surfaces through silicon–carbon bonds. The latest approaches towards preparation of monolayers through Si–C bonds on both flat and photoluminescent porous silicon are described. Wet chemical techniques, accessible to most organometallic/organic chemists are highlighted, but recent developments using UHV conditions also receive attention.
---
paper_title: Electrochemical Modification of Glassy Carbon Electrode Using Aromatic Diazonium Salts. 1. Blocking Effect of 4-Nitrophenyl and 4-Carboxyphenyl Groups

paper_content:

The effect of a 4-carboxyphenyl or a 4-nitrophenyl thin film at the surface of a glassy carbon electrode on their electrochemical responses in the presence of various electroactive probes has been investigated. The grafting of a substituted phenyl group to a glassy carbon electrode was achieved by electrochemical reduction of the corresponding substituted phenyldiazonium derivative in acetonitrile. The blocking properties of the film depend primarily on electrostatic and electrolyte/solvent effects. Permselectivity for the 4-carboxyphenyl film can be achieved by controlling the dissociation of the carboxy group. The substituted phenyl layer is much more compact and less permeable in contact with a nonaqueous solvent than with an aqueous solvent presumably because the layer is poorly solvated. Electrochemical impedance measurements indicate that the kinetics of electron transfer are slowed down when the time used to modify the glassy carbon electrode is increased. Cyclic voltammetry and X-ray photoelectron...
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paper_title: Advances in Interfacial Design for Electrochemical Biosensors and Sensors: Aryl Diazonium Salts for Modifying Carbon and Metal Electrodes

paper_content:

A high degree of control over the modification of electrode surfaces is required for many sensing applications. This critical review briefly outlines some of the considerations for interfacial design in amperometric sensors and discusses some of advantages and disadvantages of alkanethiol modified metal electrodes for such applications before concentrating on the modification of electrodes surfaces using aryl diazonium salts. The pros and cons of this chemistry, and the application of aryl diazonium salts for sensing on carbon electrodes is reviewed before recent advances in using this chemistry for modifying metal electrodes are presented.
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paper_title: Layer-by-layer assembly of cationic lipid and plasmid DNA onto gold surface for stent-assisted gene transfer

paper_content:

Intravascular stent-assisted gene transfer is an advanced approach for the therapy of vascular diseases such as atherosclerosis and stenosis. This approach requires a stent that allows local and efficient administration of therapeutic genes to the target cells at the vascular wall. To create such a stent, a method was developed for loading plasmid DNA onto the metal surface. The method involves the formation of self-assembled monolayer on the noble metal surface followed by electrostatic layer-by-layer (LBL) assembly of a cationic lipid/plasmid DNA complex and free plasmid DNA. In this in vitro feasibility study, the thin plainer film and the wire of gold were used as a substrate. The LBL assembly process was characterized by surface plasmon resonance spectroscopy and static contact angle measurement. Plasmid DNA loaded in the multilayer exhibited improved resistance against nuclease digestion. When cultured directly on the DNA-loaded surface, cells were transfected to express exogenous gene in the DNA loading-dependent manner. Plasmid DNA could also be transferred to endothelial cells from its apical side by placing the DNA-loaded gold wire onto the cell layer.
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paper_title: Electrogeneration of a poly(pyrrole)-NTA chelator film for a reversible oriented immobilization of histidine-tagged proteins

paper_content:

This contribution reports, for the first time, the synthesis and electropolymerization of a pyrrole N-substituted by a nitrilotriacetic acid acting as a chelating center of Cu2+. A step-by-step approach for protein immobilization was developed via the successive coordination of Cu2+ and histidine-tagged proteins. The self-assembly of histidine-tagged glucose oxidase led to the formation of a close-packed enzyme monolayer at the poly(pyrrole) surface, and the reversibility and reproducibility of this affinity process were demonstrated.
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paper_title: Electron transfer and ligand binding to cytochrome c' immobilized on self-assembled monolayers

paper_content:

We have successfully immobilized Allochromatium vinosum cytochrome c‘ on carboxylic acid-terminated thiol monolayers on gold and have investigated its electron-transfer and ligand binding properties. Immobilization could only be achieved for pH's ranging from 3.5 to 5.5, reflecting the fact that the protein is only sufficiently positively charged below pH 5.5 (pI = 4.9). Upon immobilization, the protein retains a near-native conformation, as is suggested by the observed potential of 85 mV vs SHE for the heme FeIII/FeII transition, which is close to the value of 60 mV reported in solution. The electron-transfer rate to the immobilized protein depends on the length of the thiol spacer, displaying distance-dependent electron tunneling for long thiols and distance-independent protein reorganization for short thiols. The unique CO-induced dimer-to-monomer transition observed for cytochrome c‘ in solution also seems to occur for immobilized cytochrome c‘. Upon saturation with CO, a new anodic peak corresponding...
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paper_title: Spectroelectrochemistry of type II cytochrome c3 on a glycosylated self-assembled monolayer.

paper_content:

A modified silver electrode was prepared by the self-assembly of a thiol-derivatized neoglycoconjugate, forming a 2D surface with maltose functionality. This self-assembled-monolayer-modified electrode was utilized for adsorption and spectroelectrochemical studies of tetraheme-containing type II cytochrome c3. The glycosylated surface allowed for the determination of the hemes' redox potentials and demonstrated enhanced spectroelectrochemical performance, in comparison to the widely used self-assembled monolayer of 11-mercapto-undecanoic acid.
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paper_title: Reversible oriented surface immobilization of functional proteins on oxide surfaces.

paper_content:

Reversible and oriented immobilization of proteins in a functionally active form on solid surfaces is a prerequisite for the investigation of molecular interactions by surface-sensitive techniques. We demonstrate a method generally applicable for the attachment of proteins to oxide surfaces. A nitrilotriacetic acid group serving as a chelator for transition metal ions was covalently bound to the surface via silane chemistry. Reversible binding of the green fluorescent protein, modified with a hexahistidine extension, was monitored in situ using total internal reflection fluorescence. The association constant and kinetic parameters of the binding process were determined. The reversible, directed immobilization of proteins on surfaces as described here opens new ways for structural investigation of proteins and receptor-ligand interactions.
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paper_title: Self-assembled monolayers for MALDI-TOF mass spectrometry for immunoassays of human protein antigens.

paper_content:

This paper reports a method that combines self-assembled monolayers with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to perform immunoassays on clinical samples. The immunosensors are prepared by immobilizing His-tagged protein G (or A) to a monolayer presenting the Ni2+ chelates, followed by immobilization of IgG antibodies with specificity for the intended analyte. The SAMDI mass spectrometry technique confirms the presence of the two proteins on the immunosensor and additionally provides a label-free analysis of antigens that bind to the sensor. This paper reports examples of detecting several proteins from human serum, including multianalyte assays that resolve each analyte according to their mass-to-charge ratio in the SAMDI spectra. An example is described wherein SAMDI is used to identify a proteolytic fragment of cystatin C in cerebral spinal fluids from patients diagnosed with multiple sclerosis. The SAMDI-TOF immunoassay, which combines well-defined surface chemistries for the selective and reproducible localization of analytes with mass spectrometry for label-free detection of analytes, may offer an alternative methodology to address many of the issues associated with standardized clinical diagnostics.
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paper_title: Electrochemical interrogation of conformational changes as a reagentless method for the sequence-specific detection of DNA

paper_content:

We report a strategy for the reagentless transduction of DNA hybridization into a readily detectable electrochemical signal by means of a conformational change analogous to the optical molecular beacon approach. The strategy involves an electroactive, ferrocene-tagged DNA stem-loop structure that self-assembles onto a gold electrode by means of facile gold-thiol chemistry. Hybridization induces a large conformational change in this surface-confined DNA structure, which in turn significantly alters the electron-transfer tunneling distance between the electrode and the redoxable label. The resulting change in electron transfer efficiency is readily measured by cyclic voltammetry at target DNA concentrations as low as 10 pM. In contrast to existing optical approaches, an electrochemical DNA (E-DNA) sensor built on this strategy can detect femtomoles of target DNA without employing cumbersome and expensive optics, light sources, or photodetectors. In contrast to previously reported electrochemical approaches, the E-DNA sensor achieves this impressive sensitivity without the use of exogenous reagents and without sacrificing selectivity or reusability. The E-DNA sensor thus offers the promise of convenient, reusable detection of picomolar DNA.
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paper_title: The self-assembled monolayer of saccharide via click chemistry: Formation and protein recognition

paper_content:

Abstract We prepared the saccharide-immobilized substrate via click chemistry. The azide-terminated saccharides were reacted by a facile metathesis reaction. The density of saccharides was controlled by the incubation time of SAM preparation. The saccharide–protein interaction was analyzed using the saccharide substrate. The interaction of the saccharide substrate with protein was strong and specific due to the glyco-cluster effects. The interaction with amyloid β was analyzed by the monosaccharide-immobilized substrate, and the sulfonated saccharides showed strong interaction.
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paper_title: Carbohydrate arrays for the evaluation of protein binding and enzymatic modification.

paper_content:

This paper reports a chemical strategy for preparing carbohydrate arrays and utilizes these arrays for the characterization of carbohydrate-protein interactions. Carbohydrate chips were prepared by the Diels-Alder-mediated immobilization of carbohydrate-cyclopentadiene conjugates to self-assembled monolayers that present benzoquinone and penta(ethylene glycol) groups. Surface plasmon resonance spectroscopy showed that lectins bound specifically to immobilized carbohydrates and that the glycol groups prevented nonspecific protein adsorption. Carbohydrate arrays presenting ten monosaccharides were then evaluated by profiling the binding specificities of several lectins. These arrays were also used to determine the inhibitory concentrations of soluble carbohydrates for lectins and to characterize the substrate specificity of beta-1,4-galactosyltransferase. Finally, a strategy for preparing arrays with carbohydrates generated on solid phase is shown. This surface engineering strategy will permit the preparation and evaluation of carbohydrate arrays that present diverse and complex structures.
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paper_title: Carbohydrate-protein interactions by "clicked" carbohydrate self-assembled monolayers.

paper_content:

A Huisgen 1,3-dipolar cycloaddition "click chemistry" was employed to immobilize azido sugars (mannose, lactose, alpha-Gal) to fabricate carbohydrate self-assembled monolayers (SAMs) on gold. This fabrication was based on preformed SAM templates incorporated with alkyne terminal groups, which could further anchor the azido sugars to form well-packed, stable, and rigid sugar SAMs. The clicked mannose, lactose, and alpha-Gal trisaccharide SAMs were used in the analysis of specific carbohydrate-protein interactions (i.e., mannose-Con A; ECL-lactose, alpha-Gal-anti-Gal). The apparent affinity constant of Con A binding to mannose was (8.7 +/- 2.8) x 10(5) and (3.9 +/- 0.2) x 10(6) M(-1) measured by QCM and SPR, respectively. The apparent affinity constants of lactose binding with ECL and alpha-Gal binding with polyclonal anti-Gal antibody were determined to be (4.6 +/- 2.4) x 10(6) and (6.7 +/- 3.3) x 10(6) M(-1), respectively by QCM. SPR, QCM, AFM, and electrochemistry studies confirmed that the carbohydrate SAM sensors maintained the specificity to their corresponding lectins and nonspecific adsorption on the clicked carbohydrate surface was negligible. This study showed that the clicked carbohydrate SAMs in concert with nonlabel QCM or SPR offered a potent platform for high-throughput characterization of carbohydrate-protein interactions. Such a combination should complement other methods such as ITC and ELISA in a favorable manner and provide insightful knowledge for the corresponding complex glycobiological processes.
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paper_title: Building conjugated organic structures on Si(111) surfaces via microwave-assisted Sonogashira coupling.

paper_content:

A novel step-by-step method employing microwave-assisted Sonogashira coupling is developed to grow fully conjugated organosilicon structures. As the first case study, p-(4-bromophenyl)acetylene is covalently conjugated to a p-(4-iodophenyl)acetylene-derived monolayer on a Si(111) surface. By bridging the two aromatic rings with C[triple bond]C, the pregrown monolayer is structurally extended outward from the Si surface, forming a fully conjugated (p-(4-bromophenylethynyl)phenyl)vinylene film. The film growth process, which reaches 90% yield after 2 h, is characterized thoroughly at each step by using X-ray reflectivity (XRR), X-ray standing waves (XSW), and X-ray fluorescence (XRF). The high yield and short reaction time offered by microwave-assisted surface Sonogashira coupling chemistry make it a promising strategy for functionalizing Si surfaces.
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paper_title: The ion gating effect: using a change in flexibility to allow label free electrochemical detection of DNA hybridisation

paper_content:

A label free electrochemical method of detecting DNA hybridisation is presented based on the change in flexibility between a single strand of DNA and a duplex causing an ion-gating effect where hybridisation opens up the electrode to access of ions.
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paper_title: Optical determination of surface density in oriented metalloprotein nanostructures

paper_content:

In the current work we circumvent a difficulty in estimating surface coverage by noting that iron-porphyrin proteins in solution have been assayed spectrophotometrically after conversion to pyridine hemochromes. By comparing the total adsorbance obtained from direct absorption measurements of oriented metalloprotein layers on SiO[sub 2] at the Soret resonance (410 nm in cytochrome b[sub 5]) to the total number density of surface protein, obtained from subsequent pyridine hemochrome assay (PHCA) analysis, the apparent surface molar absorptivity is obtained directly. In this correspondence we report the use of the PHCA to determine the surface molar absorptivity for oriented arrays of cytochrome b[sub 5] mutants. The heme is completely dissociated from the surface cytochrome b[sub 5] and converted to the reduced pyridine hemochrome in solution. Subsequently, the absorbance of reduced species in solution is determined colorimetrically. From the correlation of the absorbance of reduced hemochrome to the standard curve obtained from pyridine hemochrome assay of solution cytochrome b[sub 5], the surface concentration is estimated. 18 refs., 2 figs., 1 tab.
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paper_title: Carbohydrate and Protein Immobilization onto Solid Surfaces by Sequential Diels−Alder and Azide−Alkyne Cycloadditions

paper_content:

We demonstrate the applicability of sequential Diels−Alder and azide−alkyne [3 + 2] cycloaddition reactions (click chemistry) for the immobilization of carbohydrates and proteins onto a solid surface. An α,ω-poly(ethylene glycol) (PEG) linker carrying alkyne and cyclodiene terminal groups was synthesized and immobilized onto an N-(e-maleimidocaproyl) (EMC)-functionalized glass slide via an aqueous Diels−Alder reaction. In the process, an alkyne-terminated PEGylated surface was provided for the conjugation of azide-containing biomolecules via click chemistry, which proceeded to completion at low temperature and in aqueous solvent. As anticipated, alkyne, azide, cyclodiene, and EMC are independently stable and do not react with common organic reagents nor functional groups in biomolecules. Given an appropriate PEG linker, sequential Diels−Alder and azide−alkyne [3 + 2] cycloaddition reactions provide an effective strategy for the immobilization of a wide range of functionally complex substances onto solid s...
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paper_title: Chemoselective Attachment of Biologically Active Proteins to Surfaces by Expressed Protein Ligation and Its Application for “Protein Chip” Fabrication

paper_content:

The present work describes a general method for the selective attachment of proteins to solid surfaces through their C-termini that can be used for the efficient creation of protein chips. Our method is based in the chemoselective reaction between a protein C-terminal α-thioester and a modified surface containing N-terminal Cys residues. α-Thioester proteins can be obtained using standard recombinant techniques by using expression vectors containing engineered inteins. This new method was used to immobilize two fluorescent proteins and a functional SH3 domain using a protein microarrayer.
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paper_title: Development of DNA electrochemical biosensor based on covalent immobilization of probe DNA by direct coupling of sol-gel and self-assembly technologies.

paper_content:

A new procedure for fabricating deoxyribonucleic acid (DNA) electrochemical biosensor was developed based on covalent immobilization of target single-stranded DNA (ssDNA) on Au electrode that had been functionalized by direct coupling of sol-gel and self-assembled technologies. Two siloxanes, 3-mercaptopropyltrimethoxysiloxane (MPTMS) and 3-glycidoxypropyltrimethoxysiloxane (GPTMS) were used as precursors to prepare functionally self-assembly sol-gel film on Au electrode. The thiol group of MPTMS allowed assembly of MPTMS sol-gel on gold electrode surface. Through co-condensation between silanols, GPTMS sol-gel with epoxide groups interconnected into MPTMS sol-gel and enabled covalent immobilization of target NH(2)-ssDNA through epoxide/amine coupling reaction. The concentration of MPTMS and GPTMS influenced the performance of the resulting biosensor due to competitive sol-gel process. The linear range of the developed biosensor for determination of complementary ssDNA was from 2.51 x 10(-9) to 5.02 x 10(-7)M with a detection limit of 8.57 x 10(-10)M. The fabricated biosensor possessed good selectivity and could be regenerated. The covalent immobilization of target ssDNA on self-assembled sol-gel matrix could serve as a versatile platform for DNA immobilization and fabrication of biosensors.
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paper_title: The molecular level modification of surfaces: from self-assembled monolayers to complex molecular assemblies

paper_content:

The modification of surfaces with self-assembled monolayers (SAMs) containing multiple different molecules, or containing molecules with multiple different functional components, or both, has become increasingly popular over the last two decades. This explosion of interest is primarily related to the ability to control the modification of interfaces with something approaching molecular level control and to the ability to characterise the molecular constructs by which the surface is modified. Over this time the level of sophistication of molecular constructs, and the level of knowledge related to how to fabricate molecular constructs on surfaces have advanced enormously. This critical review aims to guide researchers interested in modifying surfaces with a high degree of control to the use of organic layers. Highlighted are some of the issues to consider when working with SAMs, as well as some of the lessons learnt (169 references).
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paper_title: Covalent coupling of antibodies to self-assembled monolayers of carboxy-functionalized poly(ethylene glycol): protein resistance and specific binding of biomolecules

paper_content:

We report the synthesis, film formation, protein resistance, and specific antigen binding capability of a carboxy-functionalized poly(ethylene glycol) alkanethiol [HOOC−CH2−(OCH2−CH2)n−O−(CH2)11−SH, n = 22−45]. Despite its polymeric character, the molecule is found to form a densely packed self-assembled monolayer on polycrystalline gold, if adsorbed from dimethylformamide solution. Due to its chain length distribution, the carboxy tailgroups are expected to be partially buried within the film and, thus, do not affect the protein repulsive characteristics of the ethylene glycol moieties when exposed to fibrinogen and immunoglobulin G (IgG). However, if activated by N-hydroxysuccinimide and N-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride, antibodies can be covalently coupled to the monolayer. While resistance to nonspecific fibrinogen and IgG adsorption is maintained for this biologically active layer, it exhibits high specific antigen binding capacity. The performance of this highly selective ...
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paper_title: Maleimide-functionalized self-assembled monolayers for the preparation of peptide and carbohydrate biochips

paper_content:

This paper reports a convenient method for immobilizing biologically active ligands to self-assembled monolayers of alkanethiolates on gold (SAMs). This methodology is based on monolayers that present maleimide and penta(ethylene glycol) groups. The maleimide groups react efficiently with thiol-terminated ligands, whereas the penta(ethylene glycol) groups prevent the nonspecific adsorption of protein to the substrate. The rate and selectivity of the immobilization of a ferrocene-thiol conjugate were characterized using cyclic voltammetry. This paper presents three examples of biochips prepared using this methodology. In the first example, four carbohydrate-thiol conjugates were immobilized to monolayers and the lectin-binding properties of the substrates were examined using fluorescence and surface plasmon resonance spectroscopy. The second biochip was used to study the enzymatic phosphorylation of the immobilized peptide IYGEFKKKC by the tyrosine kinase c-src. Monolayers presenting this peptide were then...
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paper_title: Specific capture of mammalian cells by cell surface receptor binding to ligand immobilized on gold thin films.

paper_content:

Aldehyde-terminated self-assembled monolayers (SAMs) on gold surfaces were modified with proteins and employed to capture intact living cells through specific ligand-cell surface receptor interactions. In our model system, the basic fibroblast growth factor (bFGF) binding receptor was targeted on baby hamster kidney (BHK-21) cells. Negative control and target proteins were immobilized on a gold surface by coupling protein primary amines to surface aldehyde groups. Cell-binding was monitored by phase contrast microscopy or surface plasmon resonance (SPR) imaging. The specificity of the receptor-ligand interaction was confirmed by the lack of cell binding to the negative control proteins, cytochrome c and insulin, and by the disruption of cell binding by treatment with heparitinase to destroy heparan sulfate which plays an essential role in the binding of bFGF to FGF receptors. This approach can simultaneously probe a large number of receptor-ligand interactions in cell populations and has potential for targeting and isolating cells from mixtures according to the receptors expressed on their surface.
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paper_title: Molecular self-assembly of two-terminal, voltammetric microsensors with internal references.

paper_content:

Self-assembly of a ferrocenyl thiol and a quinone thiol onto Au microelectrodes forms the basis for a new microsensor concept: a two-terminal, voltammetric microsensor with reference and sensor functions on the same electrode. The detection is based on measurement of the potential difference of current peaks for oxidation and reduction of the reference (ferrocene) and indicator (quinone) in aqueous electrolyte in a two-terminal, linear sweep voltammogram in which a counterelectrode of relatively large surface area is used. The quinone has a half-wave potential, E((1/2)), that is pH-sensitive and can be used as a pH indicator; the ferrocene center has an E(1/2) that is a pH-insensitive reference. The key advantages are that such sensors require no separate reference electrode and function as long as current peaks can be located for reference and indicator molecules.
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paper_title: Printing proteins as microarrays for high-throughput function determination.

paper_content:

Systematic efforts are currently under way to construct defined sets of cloned genes for high-throughput expression and purification of recombinant proteins. To facilitate subsequent studies of protein function, we have developed miniaturized assays that accommodate extremely low sample volumes and enable the rapid, simultaneous processing of thousands of proteins. A high-precision robot designed to manufacture complementary DNA microarrays was used to spot proteins onto chemically derivatized glass slides at extremely high spatial densities. The proteins attached covalently to the slide surface yet retained their ability to interact specifically with other proteins, or with small molecules, in solution. Three applications for protein microarrays were demonstrated: screening for protein-protein interactions, identifying the substrates of protein kinases, and identifying the protein targets of small molecules.
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paper_title: Glucose Oxidase-graphene-chitosan modified electrode for direct electrochemistry and glucose sensing

paper_content:

Abstract Direct electrochemistry of a glucose oxidase (GOD)–graphene–chitosan nanocomposite was studied. The immobilized enzyme retains its bioactivity, exhibits a surface confined, reversible two-proton and two-electron transfer reaction, and has good stability, activity and a fast heterogeneous electron transfer rate with the rate constant ( k s ) of 2.83 s −1 . A much higher enzyme loading (1.12 × 10 −9 mol/cm 2 ) is obtained as compared to the bare glass carbon surface. This GOD–graphene–chitosan nanocomposite film can be used for sensitive detection of glucose. The biosensor exhibits a wider linearity range from 0.08 mM to 12 mM glucose with a detection limit of 0.02 mM and much higher sensitivity (37.93 μA mM −1 cm −2 ) as compared with other nanostructured supports. The excellent performance of the biosensor is attributed to large surface-to-volume ratio and high conductivity of graphene, and good biocompatibility of chitosan, which enhances the enzyme absorption and promotes direct electron transfer between redox enzymes and the surface of electrodes.
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paper_title: Self-Assembled Graphene-Enzyme Hierarchical Nanostructures for Electrochemical Biosensing

paper_content:

The self-assembly of sodium dodecyl benzene sulphonate (SDBS) functionalized graphene sheets (GSs) and horseradish peroxidase (HRP) by electrostatic attraction into novel hierarchical nanostructures in aqueous solution is reported. Data from scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction demonstrate that the HRP―GSs bionanocomposites feature ordered hierarchical nanostructures with well-dispersed HRP intercalated between the GSs. UV-vis and infrared spectra indicate the native structure of HRP is maintained after the assembly, implying good biocompatibility of SDBS-functionalized GSs. Furthermore, the HRP―GSs composites are utilized for the fabrication of enzyme electrodes (HRP―GSs electrodes). Electrochemical measurements reveal that the resulting HRP―GSs electrodes display high electrocatalytic activity to H 2 O 2 with high sensitivity, wide linear range, low detection limit, and fast amperometric response. These desirable electrochemical performances are attributed to excellent biocompatibility and superb electron transport efficiency of GSs as well as high HRP loading and synergistic catalytic effect of the HRP―GSs bionanocomposites toward H 2 O 2 . As graphene can be readily non-covalently functionalized by "designer" aromatic molecules with different electrostatic properties, the proposed self-assembly strategy affords a facile and effective platform for the assembly of various biomolecules into hierarchically ordered bionanocomposites in biosensing and biocatalytic applications.
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paper_title: A novel hydrogen peroxide biosensor based on Au-graphene-HRP-chitosan biocomposites

paper_content:

Abstract Graphene was prepared successfully by introducing –SO 3 − to separate the individual sheets. TEM, EDS and Raman spectroscopy were utilized to characterize the morphology and composition of graphene oxide and graphene. To construct the H 2 O 2 biosensor, graphene and horseradish peroxidase (HRP) were co-immobilized into biocompatible polymer chitosan (CS), then a glassy carbon electrode (GCE) was modified by the biocomposite, followed by electrodeposition of Au nanoparticles on the surface to fabricate Au/graphene/HRP/CS/GCE. Cyclic voltammetry demonstrated that the direct electron transfer of HRP was realized, and the biosensor had an excellent performance in terms of electrocatalytic reduction towards H 2 O 2 . The biosensor showed high sensitivity and fast response upon the addition of H 2 O 2 , under the conditions of pH 6.5, potential −0.3 V. The time to reach the stable-state current was less than 3 s, and the linear range to H 2 O 2 was from 5 × 10 −6 M to 5.13 × 10 −3 M with a detection limit of 1.7 × 10 −6 M (S/N = 3). Moreover, the biosensor exhibited good reproducibility and long-term stability.
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paper_title: A Graphene Platform for Sensing Biomolecules

paper_content:

Sensitive platform: The use of graphene oxide (GO) as a platform for the sensitive and selective detection of DNA and proteins is presented. The interaction of GO and dye-labeled single-stranded DNA leads to quenching of the dye fluorescence. Conversely, the presence of a target DNA or protein leads to the binding of the dye-labeled DNA and target, releasing the DNA from GO, thereby restoring the dye fluorescence (see picture).
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paper_title: Direct Electrochemistry of Glucose Oxidase and Biosensing for Glucose Based on Graphene

paper_content:

We first reported that polyvinylpyrrolidone-protected graphene was dispersed well in water and had good electrochemical reduction toward O2 and H2O2. With glucose oxidase (GOD) as an enzyme model, we constructed a novel polyvinylpyrrolidone-protected graphene/polyethylenimine-functionalized ionic liquid/GOD electrochemical biosensor, which achieved the direct electron transfer of GOD, maintained its bioactivity and showed potential application for the fabrication of novel glucose biosensors with linear glucose response up to 14 mM.
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paper_title: Disposable biosensor based on graphene oxide conjugated with tyrosinase assembled gold nanoparticles.

paper_content:

A highly efficient enzyme-based screen printed electrode (SPE) was obtained by using covalent attachment between 1-pyrenebutanoic acid, succinimidyl ester (PASE) adsorbing on the graphene oxide (GO) sheets and amines of tyrosinase-protected gold nanoparticles (Tyr-Au). Herein, the bi-functional molecule PASE was assembled onto GO sheets. Subsequently, the Tyr-Au was immobilized on the PASE-GO sheets forming a biocompatible nanocomposite, which was further coated onto the working electrode surface of the SPE. The characterization of obtained nanocomposite and modified SPE surface was investigated by atomic force microscopy (AFM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Attributing to the synergistic effect of GO-Au integration and the good biocompatibility of the hybrid-material, the fabricated disposable biosensor (Tyr-Au/PASE-GO/SPE) exhibited a rapid amperometric response (less than 6s) with a high sensitivity and good storage stability for monitoring catechol. This method shows a good linearity in the range from 8.3×10(-8) to 2.3×10(-5) M for catechol with a squared correlation coefficient of 0.9980, a quantitation limit of 8.2×10(-8) M (S/N=10) and a detection limit of 2.4×10(-8) M (S/N=3). The Michaelis-Menten constant was measured to be 0.027 mM. This disposable tyrosinase biosensor could offer a great potential for rapid, cost-effective and on-field analysis of phenolic compounds.
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paper_title: Catalyst-Free Efficient Growth, Orientation and Biosensing Properties of Multilayer Graphene Nanoflake Films with Sharp Edge Planes

paper_content:

We report a novel microwave plasma enhanced chemical vapor deposition strategy for the efficient synthesis of multilayer graphene nanoflake films (MGNFs) on Si substrates. The constituent graphene nanoflakes have a highly graphitized knife-edge structure with a 2-3 nm thick sharp edge and show a preferred vertical orientation with respect to the Si substrate as established by near-edge X-ray absorption fine structure spectroscopy. The growth rate is approximately 1.6 mu m min(-1), which is 10 times faster than the previously reported best value. The MGNFs are shown to demonstrate fast electron-transfer (ET) kinetics for the Fe(CN)(6)(3-/4-) redox system and excellent electrocatalytic activity for simultaneously determining dopamine (DA), ascorbic acid (AA) and uric acid (UA). Their biosensing DA performance in the presence of common interfering agents AA and UA is superior to other bare solid-state electrodes and is comparable only to that of edge plane pyrolytic graphite. Our work here, establishes that the abundance of graphitic edge planes/defects are essentially responsible for the fast ET kinetics, active electrocatalytic and biosensing properties. This novel edge-plane-based electrochemical platform with the high surface area and electrocatalytic activity offers great promise for creating a revolutionary new class of nanostructured electrodes for biosensing, biofuel cells and energy-conversion applications.
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paper_title: Electric Field Effect in Atomically Thin Carbon Films

paper_content:

tection efficiency for the read beam is $ ; 0.04, so we infer the efficiency of quantum state transfer from the atoms onto the photon, O ; 0.03. We have realized a quantum node by combining the entanglement of atomic and photonic qubits with the atom-photon quantum state transfer. By implementing the second node at a different location and performing a joint detection of the signal photons from the two nodes, the quantum repeater protocol (11), as well as distant teleportation of an atomic qubit, may be realized. Based on this work, we estimate the rate for these protocols to be R 2 ; ($O"n s ) 2 R ; 3 � 10 j7 s j1 . However, improvements in O that are based on increasing the optical thickness of atomic samples (16), as well as elimination of transmission losses, could provide several orders of magnitude increase in R 2 . Our results also demonstrate the possibility of realizing quantum nodes consisting of multiple atomic qubits by using multiple beams of light. This approach shows promise for implementation of distributed quantum computation (20, 21).
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paper_title: Improved Detection Limit and Stability of Amperometric Carbon Nanotube-Based Immunosensors by Crosslinking Antibodies with Polylysine.

paper_content:

Amperometric immunosensor configurations featuring covalently bound anti-biotin antibodies (Ab) embedded into a polylysine (PLL)-single walled carbon nanotube (SWCNT) composite layer were evaluated. Assemblies were made by first oxidizing pyrolytic graphite (PG) electrodes to form surface carboxylic acid groups, to which PLL, SWCNTs and anti-biotin were covalently linked. Incorporating SWCNT into PLL-antibody assemblies improved the amperometric detection limit for biotin (Ag) labeled with horseradish peroxidase to 10 fmol mL(-1). Anti-biotin embedded into the PLL matrix had improved thermal stability and retained its binding ability for biotin after exposure to temperatures of 42 degrees C for up to 3 hours, while the noncrosslinked antibody was inactivated at this temperature in several minutes.
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paper_title: Amperometric biosensing of glutamate using carbon nanotube based electrode

paper_content:

Abstract Amperometric biosensing of glutamate using nanobiocomposite derived from multiwall carbon nanotube (CNT), biopolymer chitosan (CHIT), redox mediator meldola’s blue (MDB) and glutamate dehydrogenase (GlDH) is described. The CNT composite electrode shows a reversible voltammetric response for the redox reaction of MDB at −0.15 V; the composite electrode efficiently mediates the oxidation of NADH at −0.07 V, which is 630 mV less positive than that on an unmodified glassy carbon (GC) electrode. The CNTs in the composite electrode facilitates the mediated electron transfer for the oxidation of NADH. The CNT composite electrode is highly sensitive (5.9 ± 1.52 nA/μM) towards NADH and it could detect as low as 0.5 μM of NADH in neutral pH. The CNT composite electrode is highly stable and does not undergo deactivation by the oxidation products. The electrode does not suffer from the interference due to other anionic electroactive compounds such as ascorbate (AA) and urate (UA). Separate voltammetric peaks have been observed for NADH, AA and UA, allowing the individual or simultaneous determination of these bioanalytes. The glutamate biosensor was developed by combining the electrocatalytic activity of the composite film and GlDH. The enzymatically generated NADH was electrocatalytically detected using the biocomposite electrode. Glutamate has been successfully detected at −0.1 V without any interference. The biosensor is highly sensitive, stable and shows linear response. The sensitivity and the limit of detection of the biosensor was 0.71 ± 0.08 nA/μM and 2 μM, respectively.
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paper_title: Hydrogen peroxide sensor based on modified vitreous carbon with multiwall carbon nanotubes and composites of Pt nanoparticles–dopamine

paper_content:

Abstract Sensors using nanostructured materials have been under development in the last decade due to their selectivity for the detection and quantification of different compounds. The physical and chemical characteristics of carbon nanotubes provide significant advantages when used as electrodes for electronic devices, fuel cells and electrochemical sensors. This paper presents preliminary results on the modification of vitreous carbon electrodes with Multiwall Carbon Nanotubes (MWCNTs) and composites of Pt nanoparticles–dopamine (DA) as electro-catalytic materials for the hydrogen peroxide (H 2 O 2 ) reaction. Chemical pre-treatment and consequent functionalization of MWCNTs with carboxylic groups was necessary to increase the distribution of the composites. In addition, the presence of DA was important to protect the active sites and eliminate the pasivation of the surface after the electro-oxidation of H 2 O 2 takes place. The proposed H 2 O 2 sensor exhibited a linear response in the 0–5 mM range, with detection and quantification limits of 0.3441 mM and 1.1472 mM, respectively.
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paper_title: Electrochemical behaviors of amino acids at multiwall carbon nanotubes and Cu2O modified carbon paste electrode.

paper_content:

A carbon paste electrode modified with multiwall carbon nanotubes and copper(I) oxide (MWCNT-Cu(2)O CPME) was fabricated, and the electrochemical behaviors of 19 kinds of natural amino acids at this modified electrode were studied. The experimental results showed that the various kinds of amino acids without any derivatization displayed obvious oxidation current responses at the modified electrode. It was also found that the current response values of amino acids were dependent mainly on pH values of buffer solutions. The phenomenon could be explained by the fact that the amino acids suffered complexation or electrocatalytic oxidation processes under different pH values. Six kinds of amino acids (arginine, tryptophan, histidine, threonine, serine, and tyrosine), which performed high-oxidation current responses in alkaline buffers, were selected to be detected simultaneously by capillary zone electrophoresis coupled with amperometric detection (CZE-AD). These amino acids could be perfectly separated within 20 min, and their detection limits were as low as 10(-7) or 10(-8)mol L(-1) magnitude (signal/noise ratio=3). The above results demonstrated that MWCNT-Cu(2)O CPME could be successfully employed as an electrochemical sensor for amino acids with some advantages of convenient preparation, high sensitivity, and good repeatability.
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paper_title: Carbon-nanotubes doped polypyrrole glucose biosensor

paper_content:

We report on the one-step preparation route of amperometric enzyme electrodes based on incorporating a carbon-nanotube (CNT) dopant and the biocatalyst within an electropolymerized polypyrrole film. Cyclic voltammetric growth profiles indicate that the anionic CNT is incorporated within the growing film for maintaining its electrical neutrality. The entrapment of the CNT has little effect upon the electropolymerization rate and redox properties of the resulting film. The CNT dopant retains its electrocatalytic activity to impart high sensitivity and selectivity. Linearity prevails up to ca. 50 mM glucose, with a slight curvature thereafter. Relevant parameters of the film preparation were examined and optimized. Such an electropolymerization avenue represents a simple, one-step route for preparing enzyme electrodes and should further facilitate the widespread production of CNT-based electrochemical biosensors.
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paper_title: Aligned carbon nanotube–DNA electrochemical sensors

paper_content:

Single-strand DNA chains were chemically grafted onto aligned carbon nanotube electrodes, leading to novel aligned carbon nanotube–DNA sensors of a high sensitivity and selectivity for probing complementary DNA and target DNA chains of specific sequences.
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paper_title: Synthesis of individual single-walled carbon nanotubes on patterned silicon wafers

paper_content:

Recent progress1,2,3 in the synthesis of high-quality single-walled carbon nanotubes4 (SWNTs) has enabled the measurement of their physical and materials properties5,6,7,8. The idea that nanotubes might be integrated with conventional microstructures to obtain new types of nanoscale devices, however, requires an ability to synthesize, isolate, manipulate and connect individual nanotubes. Here we describe a strategy for making high-quality individual SWNTs on silicon wafers patterned with micrometre-scale islands of catalytic material. We synthesize SWNTs by chemical vapour deposition of methane on the patterned substrates. Many of the synthesized nanotubes are perfect, individual SWNTs with diameters of 1–3 nm and lengths of up to tens of micrometres. The nanotubes are rooted in the islands, and are easily located, characterized and manipulated with the scanning electron microscope and atomic force microscope. Some of the SWNTs bridge two metallic islands, offering the prospect of using this approach to develop ultrafine electrical interconnects and other devices.
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paper_title: Low-Potential Stable NADH Detection at Carbon-Nanotube-Modified Glassy Carbon Electrodes

paper_content:

Carbon-nanotube (CNT) modified glassy-carbon electrodes exhibiting strong and stable electrocatalytic response toward NADH are described. A substantial (490 mV) decrease in the overvoltage of the NADH oxidation reaction (compared to ordinary carbon electrodes) is observed using single-wall and multi-wall carbon-nanotube coatings, with oxidation starting at ca.?0.05V (vs. Ag/AgCl; pH 7.4). Furthermore, the NADH amperometric response of the coated electrodes is extremely stable, with 96 and 90% of the initial activity remaining after 60min stirring of 2x10-4M and 5x10-3M NADH solutions, respectively (compared to 20 and 14% at the bare surface). The CNT-coated electrodes thus allow highly-sensitive, low-potential, stable amperometric sensing. Such ability of carbon-nanotubes to promote the NADH electron-transfer reaction suggests great promise for dehydrogenase-based amperometric biosensors.
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paper_title: Enzyme-Doped Graphene Nanosheets for Enhanced Glucose Biosensing

paper_content:

In this work, we report the enhanced performance of polypyrrole−graphene−glucose oxidase based enzymatic biosensors employed for in vitro electrochemical glucose detection. Initially, graphene nanosheets were chemically synthesized and surface morphologies were characterized by several physical methods. Following this, graphene nanosheets were covalently conjugated to an enzyme model glucose oxidase (GOD). The presence of various reactive functionalities such as ketonic, quinonic, and carboxylic functional groups on the edge plane of graphene easily binds with the free amine terminals of the glucose oxidase to result in a strong covalent amide linkage. Further, this covalent conjugation of the enzyme to graphene was confirmed by FT-IR measurements. Following this, the surface of a glassy carbon electrode was modified by polypyrrole. Later, the conjugated graphene−GOD were then immobilized onto the glassy carbon electrode surface already modified with polypyrrole (Ppy) and the entire assembly was employed ...
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paper_title: SU-8 based microprobes with integrated planar electrodes for enhanced neural depth recording

paper_content:

Abstract Here, we describe new fabrication methods aimed to integrate planar tetrode-like electrodes into a polymer SU-8 based microprobe for neuronal recording applications. New concepts on the fabrication sequences are introduced in order to eliminate the typical electrode–tissue gap associated to the passivation layer. Optimization of the photolithography technique and high step coverage of the sputtering process have been critical steps in this new fabrication process. Impedance characterization confirmed the viability of the electrodes for reliable neuronal recordings with values comparable to commercial probes. Furthermore, a homogeneous sensing behavior was obtained in all the electrodes of each probe. Finally, in vivo action potential and local field potential recordings were successfully obtained from the rat dorsal hippocampus. Peak-to-peak amplitude of action potentials ranged from noise level to up to 400–500 μV. Moreover, action potentials of different amplitudes and shapes were recorded from all the four recording sites, suggesting improved capability of the tetrode to distinguish from different neuronal sources.
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paper_title: Conductive polymer-based sensors for biomedical applications.

paper_content:

A class of organic polymers, known as conducting polymers (CPs), has become increasingly popular due to its unique electrical and optical properties. Material characteristics of CPs are similar to those of some metals and inorganic semiconductors, while retaining polymer properties such as flexibility, and ease of processing and synthesis, generally associated with conventional polymers. Owing to these characteristics, research efforts in CPs have gained significant traction to produce several types of CPs since its discovery four decades ago. CPs are often categorised into different types based on the type of electric charges (e.g., delocalized pi electrons, ions, or conductive nanomaterials) responsible for conduction. Several CPs are known to interact with biological samples while maintaining good biocompatibility and hence, they qualify as interesting candidates for use in a numerous biological and medical applications. In this paper, we focus on CP-based sensor elements and the state-of-art of CP-based sensing devices that have potential applications as tools in clinical diagnosis and surgical interventions. Representative applications of CP-based sensors (electrochemical biosensor, tactile sensing 'skins', and thermal sensors) are briefly discussed. Finally, some of the key issues related to CP-based sensors are highlighted.
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paper_title: Conducting electroactive polymer-based biosensors

paper_content:

Abstract Conductive electroactive polymers are materials discovered just on two decades ago. Originally heralded for their high conductivity/weight ratio, it is the unique chemical properties they possess that now arouse much attention. The ability to synthesise these materials under mild conditions enables a range of biological moieties (enzymes, antibodies and even whole living cells) to be incorporated into the polymer structure. The unique electronic properties then allow direct and interactive communication with the biochemistries incorporated to produce a range of analytical signals. This work reviews the options available for immobilisation of biocomponents and signal generation using conducting polymer-based biosensors.
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paper_title: Synthesis of electrically conducting organic polymers: halogen derivatives of polyacetylene, (CH)x

paper_content:

When silvery films of the semiconducting polymer, trans‘polyacetylene’, (CH)x, are exposed to chlorine, bromine, or iodine vapour, uptake of halogen occurs, and the conductivity increases markedly (over seven orders of magnitude in the case of iodine) to give, depending on the extent of halogenation, silvery or silvery-black films, some of which have a remarkably high conductivity at room temperature.
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paper_title: Immobilization of biotinylated biomolecules onto electropolymerized poly(pyrrole-nitrilotriacetic acid)―Cu2+ film

paper_content:

Abstract A novel and simple immobilization strategy for biotinylated biological macromolecules onto electropolymerized poly(pyrrole-nitrilotriacetic acid)(NTA)–Cu 2+ films without avidin as connecting bridge is reported. After complexation of Cu 2+ by the polymerized NTA chelator, biotinylated biomolecules were immobilized by coordination of the biotin groups on the NTA–Cu 2+ complex. The anchoring of biotinylated glucose oxidase was demonstrated by fluorescent characterization via FITC-labeled avidin and amperometric measurement of glucose. The resulting calibration curve led to a sensitivity and maximum current density values of 0.6 mA mol − 1 L cm − 2 and 13.2 μA cm − 2 , respectively. Thus, biotinylated polyphenol oxidase was fixed leading to a catechol sensor with a sensitivity of 656 mA mol − 1 L cm − 2 and maximum current density of 25.4 μA cm − 2 . This system was also applied to the efficient immobilization of biotinylated DNA, illustrated by impedimetric detection of the formation of the DNA duplex.
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paper_title: Galvanostatic Entrapment of Sulfite Oxidase into Ultrathin Polypyrrole Films for Improved Amperometric Biosensing of Sulfite

paper_content:

The entrapment of sulfite oxidase (SOx) into ultrathin polypyrrole (PPy) films of 27–135 nm thickness has been successfully used for amperometric biosensing of sulfite with considerably improved performance. Optimum galvanostatic entrapment was accomplished in an electrolyte-free solution which contained 0.1 M pyrrole and 5 U/mL of SOx with a polymerization period of 120 seconds and an applied current density of 0.2 mA cm−2. Evidence of the incorporation and retention of SOx in the ultrathin PPy film was obtained by scanning electron microscopy, cyclic voltammetry and amperometric measurements. Entrapment of the enzyme in a 54 nm thick PPy-SOx film gave optimum amperometric response for sulfite and enabled the detection of as little as 0.9 μM of sulfite with a linear concentration range of 0.9 to 400 μM. The successful application of the biosensor to the determination of sulfite in beer and wine samples is reported. Comparison with a spectrophotometric method indicates that the biosensor was more superior for the determination of sulfite in red wine.
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paper_title: Screen-printed microsystems for the ultrasensitive electrochemical detection of alkaline phosphatase

paper_content:

Screen printing technique has been used to manufacture a microsystem where the graphite-based electrodes hold both a functional and an architectural task. The thick film manufacturing technique has proved valid to develop a very low volume (ca. 20 microL) device where different electrochemical operations can be very efficiently performed. Biomolecule immobilisation within the microsystem for biosensors applications has been explored by inducing and optimizing the in situ generation of a potential pulse polypyrrole electropolymerised film entrapping either glucose oxidase or glucose dehydrogenase. This biomodified microsystem was applied to the ultrasensitive electrochemical detection of alkaline phosphatase yielding limits of detection below 10(-12) M for glucose oxidase and of 10(-15) M for glucose dehydrogenase modified systems, within 15 min of incubation time. The results obtained showed the advantages of using low volume microsystems in combination with an optimised polypyrrole-enzyme film, which displayed a good immobilisation efficiency in conjunction with a good diffusion of species through. Ultrasensitive detection of AP in combination with a stable and reproducible surface modification for entrapping of biomolecules opens the window for new electrochemical detection platform with great potential for integrated biosensor applications.
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Title: Interfacial Structures and Properties of Organic Materials for Biosensors: An Overview

Section 1: Introduction
Description 1: This section will provide an overview of biosensors, their components, and applications.

Section 2: Types of Biosensors
Description 2: This section will discuss various types of biosensors and their sensing mechanisms.

Section 3: Resonant Biosensors
Description 3: This section will describe resonant biosensors, including surface acoustic wave sensors, magnetoelastic sensors, and quartz crystal biosensors.

Section 4: Thermal Detection Biosensors
Description 4: This section will explore the principles and applications of thermal detection biosensors.

Section 5: Photometric Biosensors
Description 5: This section will focus on photometric biosensors, particularly those using surface plasmon resonance and other optical properties.

Section 6: Ion-Sensitive FETs Biosensors
Description 6: This section will cover the development and functioning of ion-sensitive field-effect transistors (ISFETs) for biosensing.

Section 7: Electrochemical Biosensors
Description 7: This section will delve into the principles and types of electrochemical biosensors, including potentiometric, amperometric, and impedimetric sensors.

Section 8: Self-Assembled Monolayer
Description 8: This section will focus on the use of self-assembled monolayers (SAMs) in biosensors, including their chemistry, assembly, and biomolecule attachment strategies.

Section 9: Chemistry of SAM
Description 9: This section will describe different SAM systems based on their chemical characteristics, such as alkanethiols, organosilanes, hydrosilylation, and aryl diazonium.

Section 10: Immobilization of Biomolecules to SAM Biosensor Systems
Description 10: This section will discuss methods for immobilizing biomolecules onto SAMs through non-covalent and covalent bonds.

Section 11: Other Materials
Description 11: This section will introduce other organic materials used in biosensors, such as graphene, carbon nanotubes (CNTs), and conductive polymers.

Section 12: Conclusions
Description 12: This section will summarize the review and discuss the future prospects of biosensors and their applications.