Electrochemical Biosensors for Rapid Detection of Foodborne Salmonella: A Critical Overview
---
paper_title: Fresh Produce: A Growing Cause of Outbreaks of Foodborne Illness in the United States, 1973 through 1997

paper_content:

Fresh produce is an important part of a healthy diet. During the last three decades, the number of outbreaks caused by foodborne pathogens associated with fresh produce consumption reported to the Centers for Disease Control and Prevention has increased. To identify trends we analysed data for 1973 through 1997 from the Foodborne Outbreak Surveillance System. We defined a produce-associated outbreak as the occurrence of two or more cases of the same illness in which epidemiologic investigation implicated the same uncooked fruit, vegetable, salad, or juice. A total of 190 produce-associated outbreaks were reported, associated with 16,058 illnesses, 598 hospitalizations, and eight deaths. Produce-associated outbreaks accounted for an increasing proportion of all reported foodborne outbreaks with a known food item, rising from 0.7% in the 1970s to 6% in the 1990s. Among produce-associated outbreaks, the food items most frequently implicated included salad, lettuce, juice, melon, sprouts and berries. Among 103 (54%) produce-associated outbreaks with a known pathogen, 62 (60%) were caused by bacterial pathogens, of which 30 (48%) were caused by Salmonella. During the study period, Cyclospora and Escherichia coli O157:H7 were newly recognized as causes of foodborne illness. Foodborne outbreaks associated with fresh produce in the United States have increased in absolute numbers and as a proportion of all reported foodborne outbreaks. Fruit and vegetables are major components of a healthy diet, but eating fresh uncooked produce is not risk free. Further efforts are needed to better understand the complex interactions between microbes and produce and the mechanisms by which contamination occurs from farm to table.
---
paper_title: Salmonellosis outbreaks in the United States due to fresh produce: sources and potential intervention measures.

paper_content:

Abstract Foodborne Salmonella spp. is a leading cause of foodborne illness in the United States each year. Traditionally, most cases of salmonellosis were thought to originate from meat and poultry products. However, an increasing number of salmonellosis outbreaks are occurring as a result of contaminated produce. Several produce items specifically have been identified in outbreaks, and the ability of Salmonella to attach or internalize into vegetables and fruits may be factors that make these produce items more likely to be sources of Salmonella. In addition, environmental factors including contaminated water sources used to irrigate and wash produce crops have been implicated in a large number of outbreaks. Salmonella is carried by both domesticated and wild animals and can contaminate freshwater by direct or indirect contact. In some cases, direct contact of produce or seeds with contaminated manure or animal wastes can lead to contaminated crops. This review examines outbreaks of Salmonella due to con...
---
paper_title: Risk Factors for Microbial Contamination in Fruits and Vegetables at the Preharvest Level: A Systematic Review

paper_content:

The objective of this study was to perform a systematic review of risk factors for contamination of fruits and vegetables with Listeria monocytogenes, Salmonella, and Escherichia coli O157:H7 at the preharvest level. Relevant studies were identified by searching six electronic databases: MEDLINE, EMBASE, CAB Abstracts, AGRIS, AGRICOLA, and FSTA, using the following thesaurus terms: L. monocytogenes, Salmonella, E. coli O157 AND fruit, vegetable. All search terms were exploded to find all related subheadings. To be eligible, studies had to be prospective controlled trials or observational studies at the preharvest level and had to show clear and sufficient information on the process in which the produce was contaminated. Of the 3,463 citations identified, 68 studies fulfilled the eligibility criteria. Most of these studies were on leafy greens and tomatoes. Six studies assessed produce contamination with respect to animal host-related risk factors, and 20 studies assessed contamination with respect to pathogen characteristics. Sixty-two studies assessed the association between produce contamination and factors related to produce, water, and soil, as well as local ecological conditions of the production location. While evaluations of many risk factors for preharvest-level produce contamination have been reported, the quality assessment of the reviewed studies confirmed the existence of solid evidence for only some of them, including growing produce on clay-type soil, the application of contaminated or non-pH-stabilized manure, and the use of spray irrigation with contaminated water, with a particular risk of contamination on the lower leaf surface. In conclusion, synthesis of the reviewed studies suggests that reducing microbial contamination of irrigation water and soil are the most effective targets for the prevention and control of produce contamination. Furthermore, this review provides an inventory of the evaluated risk factors, including those requiring more research.
---
paper_title: Ecology of E. coli O157:H7 and Salmonella enterica in the Primary Vegetable Production Chain

paper_content:

There is an increased concern that plants might be more important as a carrier for human enteric pathogens like E. coli O157:H7 and Salmonella enterica serovars than previously thought. This review summarizes the knowledge available on the ecology of E. coli O157:H7 and Salmonella enterica in the primary production chain of leafy green vegetables (in particular lettuce), including manure, manure-amended soil, and crop. Based on the available literature, suggestions are made for the control of these pathogens. The suggested approach of oligotrophication of agro-ecosystems fits in the wider approach to lower environmental emissions of nutrients from manure application and to enhance the suppression against plant pathogens.Keywords
---
paper_title: Electrochemical coding technology for simultaneous detection of multiple DNA targets.

paper_content:

Nucleic-acid hybridization assays based on the use of different inorganic-colloid (quantum dots) nanocrystal tracers for the simultaneous electrochemical measurements of multiple DNA targets are described. Three encoding nanoparticles (zinc sulfide, cadmium sulfide, and lead sulfide) are used to differentiate the signals of three DNA targets in connection to stripping-voltammetric measurements of the heavy metal dissolution products. These products yield well-defined and resolved stripping peaks at -1.12 V (Zn), -0.68 V (Cd), and -0.53 V (Pb) at the mercury-coated glassy-carbon electrode (vs Ag/AgCl reference). The position and size of these peaks reflect the identity and level of the corresponding DNA target. The multi-target detection capability is coupled to the amplification feature of stripping voltammetry (to yield femtomole detection limits) and with an efficient magnetic removal of nonhybridized nucleic acids to offer high sensitivity and selectivity. The protocol is illustrated for the simultaneous detection of three DNA sequences related to the BCRA1 breast-cancer gene in a single sample in connection to magnetic beads bearing the corresponding oligonucleotide probes. The new electrochemical coding is expected to bring new capabilities for DNA diagnostics, and for bioanalysis, in general.
---
paper_title: Tunable Conjugated Polymers for Bacterial Differentiation

paper_content:

A novel rapid method for bacterial differentiation is explored based on the specific adhesion pattern of bacteria to tunable polymer surfaces. Different types of counter ions were used to electrochemically fabricate dissimilar polypyrrole (PPy) films with diverse physicochemical properties such as hydrophobicity, thickness and roughness. In order to expand the number of individual sensors in the array, three different redox states (as fabricated, oxidised and reduced) of each PPy film were also employed. These dissimilar PPy surfaces were exposed to five different bacteria, Deinococcus proteolyticus, Staphylococcus epidermidis, Alcaligenes faecalis, Pseudomonas fluorescens and Serratia marcescens, , which were seeded onto the various PPy surfaces. Fluorescent microscope images were taken and used to quantify the number of cells adhering to the surfaces. Generally, the number of cells of a particular bacterial strain that adhered varied when exposed to dissimilar polymer surfaces, due to the effects of the surface properties of the polymer on bacterial attachment. Similarly, the number of cells that adhered varied with different bacteria exposed to the same surface, reflecting the different surface properties of the bacteria. Statistical analysis and principal component analysis showed that all had their own specific adhesion pattern with respect to the array of PPy surfaces. Hence, these bacteria could be discriminated by this simple label-free method. In summary, this provides a proof-of-concept for using specific adhesion properties of bacterial in conjunction with tunable polymer arrays and pattern recognition as a method for rapid bacterial identification in situ.
---
paper_title: New materials for electrochemical sensing VI: Carbon nanotubes

paper_content:

Carbon nanotubes (CNTs) combine in a unique way high electrical conductivity, high chemical stability and extremely high mechanical strength. These special properties of both single-wall (SW) and multi-wall (MW) CNTs have attracted the interest of many researchers in the field of electrochemical sensors. This article demonstrates the latest advances and future trends in producing, modifying, characterizing and integrating CNTs into electrochemical sensing systems. ::: ::: CNTs can be either used as single probes after formation in situ or even individually attached onto a proper transducing surface after synthesis. Both SWCNTs and MWCNTs can be used to modify several electrode surfaces in either vertically oriented “nanotube forests” or even a non-oriented way. They can be also used in sensors after mixing them with a polymer matrix to form CNT composites. ::: ::: We discuss novel applications of CNTs in electrochemical sensors, including enzyme-based biosensors, DNA sensors and immunosensors, and propose future challenges and applications.
---
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.
---
paper_title: Quantum Dots for Sensing

paper_content:

Quantum confinement has become a powerful tool for creating new materials with extraordinary properties. Since 1980s, the quantum effects on materials have become relevant as far as the scientific community has focused its attention on smaller devices. When certain particle scale is trespassed, quantum confinement effects start to play a relevant role in the macroscopic properties of the matter. Since their beginning, quantum-confined structures have been widely used in optoelectronic device technology rather than in sensor applications. Nevertheless, sensor applications based on quantum dots experiment a real boost thanks to the semiconductor nanocrystals. The possibility of having high-quality, industrially scaled-up, biocompatible quantum dot nanocrystals has supposed a real breakthrough in the biological and medical fields. Quantum dots significantly improve the sensing tools in applications such as cellular assays, cancer detection, or DNA sequencing. This chapter summarizes the state of the art of the use of quantum dots in the sensor field.
---
paper_title: Quantum-Dot/Aptamer-Based Ultrasensitive Multi-Analyte Electrochemical Biosensor

paper_content:

The coupling of aptamers with the coding and amplification features of inorganic nanocrystals is shown for the first time to offer a highly sensitive and selective simultaneous bioelectronic detection of several protein targets. This is accomplished in a single-step displacement assay in connection to a self-assembled monolayer of several thiolated aptamers conjugated to proteins carrying different inorganic nanocrystals. Electrochemical stripping detection of the nondisplaced nanocrystal tracers results in a remarkably low (attomole) detection limit, that is, significantly lower than those of existing aptamer biosensors. The new device offers great promise for measuring a large panel of disease markers present at ultralow levels during early stages of the disease progress.
---
paper_title: Magnetic Particles Coupled to Disposable Screen Printed Transducers for Electrochemical Biosensing

paper_content:

Ultrasensitive biosensing is currently a growing demand that has led to the development of numerous strategies for signal amplification. In this context, the unique properties of magnetic particles; both of nano- and micro-size dimensions; have proved to be promising materials to be coupled with disposable electrodes for the design of cost-effective electrochemical affinity biosensing platforms. This review addresses, through discussion of selected examples, the way that nano- and micro-magnetic particles (MNPs and MMPs; respectively) have contributed significantly to the development of electrochemical affinity biosensors, including immuno-, DNA, aptamer and other affinity modes. Different aspects such as type of magnetic particles, assay formats, detection techniques, sensitivity, applicability and other relevant characteristics are discussed. Research opportunities and future development trends in this field are also considered.
---
paper_title: Screen-Printed Electrodes Modified with Carbon Nanomaterials: A Comparison among Carbon Black, Carbon Nanotubes and Graphene

paper_content:

In this work a comparative study using Screen-Printed Electrodes (SPEs) modified by drop casting with Carbon Black, Single Walled Carbon Nanotubes[BOND]COOH, Graphene Oxide, and reduced Graphene Oxide is reported. The carbon nanomaterials employed were characterized by X-ray photoelectron and Raman spectroscopy, while the modified SPEs have been morphologically and electrochemically characterized. Nanoengineered SPEs have been tested with ferricyanide, NADH, ascorbic acid and cysteine. We observed valuable electroanalytical performances of Carbon Black with the advantage to be i) cost-effective ii) suitable to obtain stable and homogenous dispersion and iii) mass-producible following a well established route.
---
paper_title: Gold Nanoparticles in Chemical and Biological Sensing

paper_content:

Detection of chemical and biological agents plays a fundamental role in biomedical, forensic and environmental sciences1–4 as well as in anti bioterrorism applications.5–7 The development of highly sensitive, cost effective, miniature sensors is therefore in high demand which requires advanced technology coupled with fundamental knowledge in chemistry, biology and material sciences.8–13 ::: ::: In general, sensors feature two functional components: a recognition element to provide selective/specific binding with the target analytes and a transducer component for signaling the binding event. An efficient sensor relies heavily on these two essential components for the recognition process in terms of response time, signal to noise (S/N) ratio, selectivity and limits of detection (LOD).14,15 Therefore, designing sensors with higher efficacy depends on the development of novel materials to improve both the recognition and transduction processes. Nanomaterials feature unique physicochemical properties that can be of great utility in creating new recognition and transduction processes for chemical and biological sensors15–27 as well as improving the S/N ratio by miniaturization of the sensor elements.28 ::: ::: Gold nanoparticles (AuNPs) possess distinct physical and chemical attributes that make them excellent scaffolds for the fabrication of novel chemical and biological sensors (Figure 1).29–36 First, AuNPs can be synthesized in a straightforward manner and can be made highly stable. Second, they possess unique optoelectronic properties. Third, they provide high surface-to-volume ratio with excellent biocompatibility using appropriate ligands.30 Fourth, these properties of AuNPs can be readily tuned varying their size, shape and the surrounding chemical environment. For example, the binding event between recognition element and the analyte can alter physicochemical properties of transducer AuNPs, such as plasmon resonance absorption, conductivity, redox behavior, etc. that in turn can generate a detectable response signal. Finally, AuNPs offer a suitable platform for multi-functionalization with a wide range of organic or biological ligands for the selective binding and detection of small molecules and biological targets.30–32,36 Each of these attributes of AuNPs has allowed researchers to develop novel sensing strategies with improved sensitivity, stability and selectivity. In the last decade of research, the advent of AuNP as a sensory element provided us a broad spectrum of innovative approaches for the detection of metal ions, small molecules, proteins, nucleic acids, malignant cells, etc. in a rapid and efficient manner.37 ::: ::: ::: ::: Figure 1 ::: ::: Physical properties of AuNPs and schematic illustration of an AuNP-based detection system. ::: ::: ::: ::: In this current review, we have highlighted the several synthetic routes and properties of AuNPs that make them excellent probes for different sensing strategies. Furthermore, we will discuss various sensing strategies and major advances in the last two decades of research utilizing AuNPs in the detection of variety of target analytes including metal ions, organic molecules, proteins, nucleic acids, and microorganisms.
---
paper_title: Methods and applications of antibody microarrays in cancer research

paper_content:

Antibody microarrays have great potential for significant value in biological research. Cancer research in particular could benefit from the unique experimental capabilities of this technology. This article examines the current state of antibody microarray technological developments and assay formats, along with a review of the demonstrated applications to cancer research. Work is ongoing in the refinement of various aspects of the protocols and the development of robust methods for routine use. Antibody microarray experimental formats can be broadly categorized into two classes: (1) direct labeling experiments, and (2) dual antibody sandwich assays. In the direct labeling method, the covalent labeling of all proteins in a complex mixture provides a means for detecting bound proteins after incubation on an antibody microarray. If proteins are labeled with a tag, such as biotin, the signal from bound proteins can be amplified. In the sandwich assay, proteins captured on an antibody microarray are detected by a cocktail of detection antibodies, each antibody matched to one of the spotted antibodies. Each format has distinct advantages and disadvantages. Several applications of antibody arrays to cancer research have been reported, including the analysis of proteins in blood serum, resected frozen tumors, cell lines, and on membranes of blood cells. These demonstrations clearly show the utility of antibody microarrays for cancer research and signal the imminent expansion of this platform to many areas of biological research.
---
paper_title: Designing label-free electrochemical immunosensors for cytochrome c using nanocomposites functionalized screen printed electrodes

paper_content:

We have designed here a label-free direct electrochemical immunosensor for the detection of cytochrome c (cyt c), a heme containing metalloprotein using its specific monoclonal antibody. Two nanocomposite-based electrochemical immunosensor platforms were evaluated for the detection of cyt c; (i) self-assembled monolayer (SAM) on gold nanoparticles (GNP) in polypyrrole (PPy) grafted screen printed electrodes (SPE) and (ii) carbon nanotubes (CNT) integrated PPy/SPE. The nanotopologies of the modified electrodes were confirmed by scanning electron microscopy. Electrochemical impedance spectroscopy and cyclic voltammetry were employed to monitor the stepwise fabrication of the nanocomposite immunosensor platforms. In the present method, the label-free quantification of cyt c is based on the direct electron transfer between Fe (III)/Fe (II)-heme redox active site of cyt c selectively bound to anti-cyt c nanocomposite modified SPE. GNP/PPy and CNT/PPy nanocomposites promoted the electron transportation through the conductive pore channels. The overall analytical performance of GNP/PPy based immunosensor (detection limit 2 nM; linear range: 2 nM to 150 µM) was better than the anti-cyt c/CNT/PPy (detection limit 10 nM; linear range: 10 nM to 50 µM). Further, the measurement of cyt c release in cell lysates of cardiomyocytes using the GNP/PPy based immunosensor gave an excellent correlation with standard ELISA.
---
paper_title: Electrochemical biosensors based on nanomodified screen-printed electrodes: Recent applications in clinical analysis

paper_content:

Abstract This review addresses recent advances in the development of screen-printed electrode based biosensors modified with different nanomaterials such as carbon nanotubes, graphene, metallic nanoparticles as gold, silver and magnetic nanoparticles, and mediator nanoparticles (Prussian Blue, Cobalt Phthalocyanine, etc.), coupled with biological recognition elements such as enzymes, antibodies, DNA and aptamers to obtain probes with improved analytical features. Examples of clinical applications are illustrated, together with examples of paper-based electrochemical devices, of multiple detections using arrays of screen printed electrodes, and of the most recent developments in the field of wearable biosensors. Also the use of smartphones as final detectors is briefly depicted.
---
paper_title: A novel electrochemical sensing strategy for rapid and ultrasensitive detection of Salmonella by rolling circle amplification and DNA-AuNPs probe.

paper_content:

A novel electrochemical sensing strategy was developed for ultrasensitive and rapid detection of Salmonella by combining the rolling circle amplification with DNA-AuNPs probe. The target DNA could be specifically captured by probe 1 on the sensing interface. Then the circularization mixture was added to form a typical sandwich structure. In the presence of dNTPs and phi29 DNA polymerase, the RCA was initiated to produce micrometer-long single-strand DNA. Finally, the detection probe (DNA-AuNPs) could recognize RCA product to produce enzymatic electrochemical signal. Under optimal conditions, the calibration curve of synthetic target DNA had good linearity from 10aM to 10pM with a detection limit of 6.76aM (S/N=3). The developed method had been successfully applied to detect Salmonella as low as 6CFUmL(-1) in real milk sample. This proposed strategy showed great potential for clinical diagnosis, food safety and environmental monitoring.
---
paper_title: An electrochemical genosensor for Salmonella typhi on gold nanoparticles-mercaptosilane modified screen printed electrode.

paper_content:

In this work, we fabricated a system of integrated self-assembled layer of organosilane 3-mercaptopropyltrimethoxy silane (MPTS) on the screen printed electrode (SPE) and electrochemically deposited gold nanoparticle for Salmonella typhi detection employing Vi gene as a molecular marker. Thiolated DNA probe was immobilized on a gold nanoparticle (AuNP) modified SPE for DNA hybridization assay using methylene blue as redox (electroactive) hybridization indicator, and signal was monitored by differential pulse voltammetry (DPV) method. The modified SPE was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and atomic force microscopy (AFM) method. The DNA biosensor showed excellent performances with high sensitivity and good selectivity. The current response was linear with the target sequence concentrations ranging from 1.0 × 10(-11) to 0.5 × 10(-8)M and the detection limit was found to be 50 (± 2.1)pM. The DNA biosensor showed good discrimination ability to the one-base, two-base and three-base mismatched sequences. The fabricated genosensor could also be regenerated easily and reused for three to four times for further hybridization studies.
---
paper_title: Aptamer-based viability impedimetric sensor for bacteria.

paper_content:

The development of an aptamer-based viability impedimetric sensor for bacteria (AptaVISens-B) is presented. Highly specific DNA aptamers to live Salmonella typhimurium were selected via the cell-systematic evolution of ligands by exponential enrichment (SELEX) technique. Twelve rounds of selection were performed; each comprises a positive selection step against viable S. typhimurium and a negative selection step against heat killed S. typhimurium and a mixture of related pathogens, including Salmonella enteritidis, Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Citrobacter freundii to ensure the species specificity of the selected aptamers. The DNA sequence showing the highest binding affinity to the bacteria was further integrated into an impedimetric sensor via self-assembly onto a gold nanoparticle-modified screen-printed carbon electrode (GNP-SPCE). Remarkably, this aptasensor is highly selective and can successfully detect S. typhimurium down to 600 CFU mL(-1) (equivalent to 18 live cells in 30 μL of assay volume) and distinguish it from other Salmonella species, including S. enteritidis and S. choleraesuis. This report is envisaged to open a new venue for the aptamer-based viability sensing of a variety of microorganisms, particularly viable but nonculturable (VBNC) bacteria, using a rapid, economic, and label-free electrochemical platform.
---
paper_title: Signal amplification technology based on entropy-driven molecular switch for ultrasensitive electrochemical determination of DNA and Salmonella typhimurium

paper_content:

Abstract A methodology based on entropy-driven molecule switch signal amplification strategy has been developed for the ultrasensitive detection of DNA. The gold electrode modified with gold nanoparticles was used to immobilize capture hairpin DNA. In the presence of target DNA, the stem of hairpin DNA was opened once the hybridization reaction occurred between the capture DNA and target DNA. With the addition of the link DNA which has more complementary bases with the capture DNA, the link DNA would hybridize with the capture DNA, and the target DNA would be displaced under the entropy-driven. The released target DNA could open another hairpin DNA. Through such a cycle the target DNA could be recycled, and more hairpin DNA was opened and more link DNA would hybridize with the capture DNA. When the electrochemical nanoparticle probe which consisted of the nanoparticles, probe DNA and the electrochemical reagent was added, the link DNA would hybridize with the probe DNA. As a result, the electrochemical response can be amplified and monitored. In this work, the Salmonella typhimurium aptamer complementary DNA was chosen as a model target, and S. typhimurium was also tested by target induced strand release technology coupling the entropy-driven molecule switch signal amplified strategy. The electrochemical sensor demonstrated excellent sensing performances such as ultra low detection limit (0.3 fmol L −1 for DNA and 13 cfu mL −1 for S. typhimurium ) and high specificity, indicating that it is highly promising to provide a sensitive, selective, cost-effective, and convenient approach for DNA and S. typhimurium detection.
---
paper_title: Diazonium-based impedimetric aptasensor for the rapid label-free detection of Salmonella typhimurium in food sample.

paper_content:

Fast and accurate detection of microorganisms is of key importance in clinical analysis and in food and water quality monitoring. Salmonella typhimurium is responsible for about a third of all cases of foodborne diseases and consequently, its fast detection is of great importance for ensuring the safety of foodstuffs. We report the development of a label-free impedimetric aptamer-based biosensor for S. typhimurium detection. The aptamer biosensor was fabricated by grafting a diazonium-supporting layer onto screen-printed carbon electrodes (SPEs), via electrochemical or chemical approaches, followed by chemical immobilisation of aminated-aptamer. FTIR-ATR, contact angle and electrochemical measurements were used to monitor the fabrication process. Results showed that electrochemical immobilisation of the diazonium-grafting layer allowed the formation of a denser aptamer layer, which resulted in higher sensitivity. The developed aptamer-biosensor responded linearly, on a logarithm scale, over the concentration range 1 × 10(1) to 1 × 10(8)CFU mL(-1), with a limit of quantification (LOQ) of 1 × 10(1) CFU mL(-1) and a limit of detection (LOD) of 6 CFU mL(-1). Selectivity studies showed that the aptamer biosensor could discriminate S. typhimurium from 6 other model bacteria strains. Finally, recovery studies demonstrated its suitability for the detection of S. typhimurium in spiked (1 × 10(2), 1 × 10(4) and 1 × 10(6) CFU mL(-1)) apple juice samples.
---
paper_title: Phagomagnetic Separation and Electrochemical Magneto-Genosensing of Pathogenic Bacteria

paper_content:

This paper addresses the use of bacteriophages immobilized on magnetic particles for the biorecognition of the pathogenic bacteria, followed by electrochemical magneto-genosensing of the bacteria. The P22 bacteriophage specific to Salmonella (serotypes A, B, and D1) is used as a model. The bacteria are captured and preconcentrated by the bacteriophage-modified magnetic particles through the host interaction with high specificity and efficiency. DNA amplification of the captured bacteria is then performed by double-tagging polymerase chain reaction (PCR). Further detection of the double-tagged amplicon is achieved by electrochemical magneto-genosensing. The strategy is able to detect in 4 h as low as 3 CFU mL(-1) of Salmonella in Luria-Bertani (LB) media. This approach is compared with conventional culture methods and PCR-based assay, as well as with immunological screening assays for bacteria detection, highlighting the outstanding stability and cost-efficient and animal-free production of bacteriophages as biorecognition element in biosensing devices.
---
paper_title: Sensitive electrochemical detection of Salmonella with chitosan–gold nanoparticles composite film

paper_content:

Abstract An ultrasensitive electrochemical immunosensor for detection of Salmonella has been developed based on using high density gold nanoparticles (GNPs) well dispersed in chitosan hydrogel and modified glassy carbon electrode. The composite film has been oxidized in NaCl solution and used as a platform for the immobilization of capture antibody (Ab1) for biorecognition. After incubation in Salmonella suspension and horseradish peroxidase (HRP) conjugated secondary antibody (Ab2) solution, a sandwich electrochemical immunosensor has been constructed. The electrochemical signal was obtained and improved by comparing the composite film with chitosan film. The result has shown that the constructed sensor provides a wide linear range from 10 to 105 CFU/mL with a low detection limit of 5 CFU/mL (at the ratio of signal to noise, S/N=3:1). Furthermore, the proposed immunosensor has demonstrated good selectivity and reproducibility, which indicates its potential in the clinical diagnosis of Salmonella contaminations.
---
paper_title: Electrochemical Aptasensor for Rapid and Sensitive Determination of Salmonella Based on Target-Induced Strand Displacement and Gold Nanoparticle Amplification

paper_content:

ABSTRACTA simple, rapid, and sensitive electrochemical aptasensor based on target-induced strand displacement and gold nanoparticle amplification was developed for the determination of Salmonella. The aptamer for Salmonella was captured on the sensing interface by hybridizing with a capture probe. In the presence of Salmonella, the aptamer dissociated from the capture probe as the stronger interaction between the aptamer and the Salmonella. The single-strand capture probe was then hybridized with the biotinylated detection probe assembled on gold nanoparticles and catalyzed by streptavidin–alkaline phosphatase, providing a sensitive electrochemical response. The gold nanoparticles significantly amplified the detection probe signal and increased the sensitivity. The linear dynamic range was from 2 × 101 to 2 × 106 CFU mL−1 with a detection limit of 20 CFU mL−1. This strategy was utilized for the determination of Salmonella in milk, demonstrating potential application in clinical diagnostics, food safety, a...
---
paper_title: An aptamer-based electrochemical biosensor for the detection of Salmonella.

paper_content:

Salmonella is one of the most common causes of food-associated disease. An electrochemical biosensor was developed for Salmonella detection using a Salmonella-specific recognition aptamer. The biosensor was based on a glassy carbon electrode modified with graphene oxide and gold nanoparticles. Then, the aptamer ssDNA sequence could be linked to the electrode. Each assembly step was accompanied by changes to the electrochemical parameters. After incubation of the modified electrode with Salmonella, the electrochemical properties between the electrode and the electrolyte changed accordingly. The electrochemical impedance spectrum was measured to quantify the Salmonella. The results revealed that, when more Salmonella were added to the reaction system, the current between the electrode and electrolyte decreased; in other words, the impendence gradually increased. A detection limit as low as 3 cfu/mL was obtained. This novel method is specific and fast, and it has the potential for real sample detection.
---
paper_title: ELIME assay vs Real-Time PCR and conventional culture method for an effective detection of Salmonella in fresh leafy green vegetables.

paper_content:

The detection of Salmonella according to EC regulation is still primarily based on traditional microbiological culture methods that may take several days to be completed. The purpose of this work is to demonstrate the applicability of an Enzyme-Linked-Immuno-Magnetic-Electrochemical (ELIME) assay, recently developed by our research group for the detection of salmonella in irrigation water, in fresh (raw and ready-to-eat) leafy green vegetables by comparison with Real-Time PCR (RTi-PCR) and ISO culture methods. Since vegetables represent a more complex matrix than irrigation water, preliminary experiments were carried out on two leafy green vegetables that resulted negative for salmonella by the ISO method. 25g of these samples were experimentally inoculated with 1-10 CFU of S. Napoli or S. Thompson and pre-enriched for 20h in two different broths. At this time aliquots were taken, concentrated at different levels by centrifugation, and analyzed by ELIME and RTi-PCR. Once selected the best culture medium for salmonella growth, and the optimal concentration factor suitable to reduce the sample matrix effect, enhancing the out-put signal, several raw and ready-to-eat leafy green vegetables were artificially inoculated and pre-enriched. Aliquots were then taken at different incubation times and analyzed with both techniques. Results obtained showed that 20 and 8h of pre-enrichment were required to allow the target salmonella (1-10 CFU/25g) to multiply until reaching a detectable concentration by ELIME and RTi-PCR assays, respectively. A confirmation with the ISO culture method was carried out. Based on the available literature, this is the first report of the application of an ELISA based method for the detection of Salmonella in vegetables.
---
paper_title: Rapid detection of Escherichia coli O157:H7 and Salmonella Typhimurium in foods using an electrochemical immunosensor based on screen-printed interdigitated microelectrode and immunomagnetic separation

paper_content:

Abstract Foodborne pathogens have continuously been a serious food safety issue and there is a growing demand for a rapid and sensitive method to screen the pathogens for on-line or in-field applications. Therefore, an impedimetric immunosensor based on the use of magnetic beads (MBs) for separation and a screen-printed interdigitated microelectrode (SP-IDME) for measurement was studied for the rapid detection of Escherichia coli O157:H7 and Salmonella Typhimurium in foods. Streptavidin coated MBs were functionalized with corresponding biotinylated antibodies (Ab) to capture the target bacteria. The glucose oxidase (GOx)–Ab conjugates were employed to label the MBs–Ab–cell complexes. The yielded MBs–Ab–cell–Ab–GOx biomass was mixed with the glucose solution to trigger an enzymatic reaction which produced gluconic acid. This increased the ion strength of the solution, thus decreasing the impedance of the solution measured on the SP-IDME. Our results showed that the immunosensor was capable of specifically detecting E. coli O157:H7 and S. Typhimurium within the range of 10 2 –10 6 cfu ml −1 in the pure culture samples. E. coli O157:H7 in ground beef and S. Typhimurium in chicken rinse water were also examined. The limits of detection (LODs) for the two bacteria in foods were 2.05×10 3 cfu g −1 and 1.04×10 3 cfu ml −1 , respectively. This immunosensor required only a bare electrode to measure the impedance changes, and no surficial modification on the electrode was needed. It was low-cost, reproducible, easy-to-operate, and easy-to-preserve. All these merits demonstrated this immunosensor has great potential for the rapid and on-site detection of pathogenic bacteria in foods.
---
paper_title: Immunomagnetic separation of Salmonella with tailored magnetic micro and nanocarriers. A comparative study.

paper_content:

This paper addresses a comparative study of immunomagnetic separation of Salmonella using micro and nano-sized magnetic carriers. In this approach, nano (300 nm) and micro (2.8 μm) sized magnetic particles were modified with anti-Salmonella antibody to pre-concentrate the bacteria from the samples throughout an immunological reaction. The performance of the immunomagnetic separation on the different magnetic carriers was evaluated using classical culturing, confocal and scanning electron microscopy to study the binding pattern, as well as a magneto-actuated immunosensor with electrochemical read-out for the rapid detection of the bacteria in spiked milk samples. In this approach, a second polyclonal antibody labeled with peroxidase as electrochemical reporter was used. The magneto-actuated electrochemical immunosensor was able to clearly distinguish between food pathogenic bacteria such as Salmonella enterica and Escherichia coli, showing a limit of detection (LOD) as low as 538 CFU mL(-1) and 291 CFU mL(-1) for magnetic micro and nanocarriers, respectively, in whole milk, although magnetic nanoparticles showed a noticeable higher matrix effect and higher agglomeration effect. These LODs were achieved in a total assay time of 1h without any previous culturing pre-enrichment step. If the samples were pre-enriched for 8 h, the magneto immunosensor based on the magnetic nanoparticles was able to detect as low as 1 CFU in 25 mL of milk (0.04 CFU mL(-1)).
---
paper_title: Rapid detection of Salmonella using a redox cycling-based electrochemical method

paper_content:

Abstract An electrochemical method based on redox cycling combined with immunomagnetic separation and pre-concentration was developed for rapid and sensitive detection of Salmonella. Electrochemical methods for the detection of bacteria offer the advantages of instant quantification with minimal equipment. Unfortunately, the limits of detection are often poor compare to other transduction methods such as fluorescence and chemiliuminescence. We demonstrated an electrochemical method which is both rapid and has a low limit of detection. A two-step strategy, which included immunomagentic pre-concentration and redox cycling was used to amplify the signal. Magnetic beads modified with anti-Salmonella antibodies were used for separation and pre-concentration of Salmonella from phosphate buffered saline (PBS) and agricultural water. Then anti-Salmonella antibodies conjugated with alkaline phosphatase were employed for labeling the Salmonella which had been captured by magnetic beads. Alkaline phosphatase (ALP) catalyzed the substrate l -ascorbic acid 2-phosphate (AAP) to electroactive species l -ascorbic acid (AA) while tris(2-carboxyethyl)phosphine (TCEP) facilitated the regeneration of AA on the gold electrode to form redox cycling resulting in an amplified signal. Under the optimal conditions, the Salmonella in PBS buffer as well as in agricultural water were detected. The limit of detection of this approach was approximately 7.6 × 102 CFU/mL and 6.0 × 102 CFU/mL in PBS buffer and agricultural water, respectively, without pre-enrichment in 3 h. When the agricultural water has been pre-enriched for 4 h, the limit of detection was approximately 10 CFU/mL.
---
paper_title: Signal amplification technology based on entropy-driven molecular switch for ultrasensitive electrochemical determination of DNA and Salmonella typhimurium

paper_content:

Abstract A methodology based on entropy-driven molecule switch signal amplification strategy has been developed for the ultrasensitive detection of DNA. The gold electrode modified with gold nanoparticles was used to immobilize capture hairpin DNA. In the presence of target DNA, the stem of hairpin DNA was opened once the hybridization reaction occurred between the capture DNA and target DNA. With the addition of the link DNA which has more complementary bases with the capture DNA, the link DNA would hybridize with the capture DNA, and the target DNA would be displaced under the entropy-driven. The released target DNA could open another hairpin DNA. Through such a cycle the target DNA could be recycled, and more hairpin DNA was opened and more link DNA would hybridize with the capture DNA. When the electrochemical nanoparticle probe which consisted of the nanoparticles, probe DNA and the electrochemical reagent was added, the link DNA would hybridize with the probe DNA. As a result, the electrochemical response can be amplified and monitored. In this work, the Salmonella typhimurium aptamer complementary DNA was chosen as a model target, and S. typhimurium was also tested by target induced strand release technology coupling the entropy-driven molecule switch signal amplified strategy. The electrochemical sensor demonstrated excellent sensing performances such as ultra low detection limit (0.3 fmol L −1 for DNA and 13 cfu mL −1 for S. typhimurium ) and high specificity, indicating that it is highly promising to provide a sensitive, selective, cost-effective, and convenient approach for DNA and S. typhimurium detection.
---
paper_title: Phagomagnetic Separation and Electrochemical Magneto-Genosensing of Pathogenic Bacteria

paper_content:

This paper addresses the use of bacteriophages immobilized on magnetic particles for the biorecognition of the pathogenic bacteria, followed by electrochemical magneto-genosensing of the bacteria. The P22 bacteriophage specific to Salmonella (serotypes A, B, and D1) is used as a model. The bacteria are captured and preconcentrated by the bacteriophage-modified magnetic particles through the host interaction with high specificity and efficiency. DNA amplification of the captured bacteria is then performed by double-tagging polymerase chain reaction (PCR). Further detection of the double-tagged amplicon is achieved by electrochemical magneto-genosensing. The strategy is able to detect in 4 h as low as 3 CFU mL(-1) of Salmonella in Luria-Bertani (LB) media. This approach is compared with conventional culture methods and PCR-based assay, as well as with immunological screening assays for bacteria detection, highlighting the outstanding stability and cost-efficient and animal-free production of bacteriophages as biorecognition element in biosensing devices.
---
paper_title: Electrochemical immunoassay for Salmonella Typhimurium based on magnetically collected Ag-enhanced DNA biobarcode labels

paper_content:

We describe a sensitive electrochemical immunoassay for Salmonella enterica serovar Typhimurium, a common foodborne pathogen which can cause infection at extremely small doses. The assay is based on the recognition of DNA biobarcode labels by differential pulse anodic stripping voltammetry (DPASV), following Ag enhancement. The biobarcodes consist of latex spheres (mean diameter 506 nm ± 22 nm) modified by ferromagnetic Fe3O4 particles. Each biobarcode is loaded by adsorption with approx. 27 molecules of mouse monoclonal antibody against S. Typhimurium and 3.5 × 10(5) molecules of 12 mer ssDNA. The assay is performed by adding the biobarcode, S. Typhimurium cells, and biotin-conjugated rabbit polyclonal antibody against Salmonella into well plates. After antigen-antibody binding, magnetic collection enables the excess polyclonal antibody to be washed off. Exposure to avidin-coated screen printed electrodes, and formation of the avidin-biotin bond, then enables the excess biobarcode to be removed. The biobarcode remaining on the electrode is quantified by DPASV measurement of Ag(+) ions following catalytic Ag deposition. The assay showed a negligible response to 10(7) CFU mL(-1)E. coli and had a limit of detection of 12 CFU mL(-1) in buffer, and 13 to 26 CFU mL(-1) for heat-killed and whole cell S. Typhimurium in plain milk, green bean sprouts and raw eggs. To the best of our knowledge, this is the lowest reported limit of detection for Salmonella by an electrochemical immunoassay not requiring sample pre-enrichment.
---
paper_title: Development and evaluation of an ELIME assay to reveal the presence of Salmonella in irrigation water: Comparison with Real-Time PCR and the Standard Culture Method

paper_content:

Abstract A reliable, low-cost and easy-to-use ELIME (Enzyme-Linked-Immuno-Magnetic-Electrochemical) assay for detection of Salmonella enterica in irrigation water is presented. Magnetic beads (MBs), coupled to a strip of eight-magnetized screen-printed electrodes localized at the bottom of eight wells (8-well/SPE strip), effectively supported a sandwich immunological chain. Enzymatic by-product is quickly measured by chronoamperometry, using a portable instrument. With the goal of developing a method able to detect a wide range of Salmonella serotypes, including S. Napoli and S. Thompson strains responsible for various community alerts, different kinds of MBs, antibodies and blocking agents were tested. The final system employs MBs coated with a broad reactivity monoclonal antibody anti-salmonella and blocked with dry milk. For a simple and rapid assay these two steps were performed in a preliminary phase, while the two sequential incubations for the immuno-recognition events were merged in a single step of 1 h. In parallel a Real-Time PCR (RTi-PCR) method, based on a specific locked nucleic acid (LNA) fluorescent probe and an internal amplification control (IAC), was carried out. The selectivity of the ELIME and RTi-PCR assays was proved by inclusivity and exclusivity tests performed analyzing different Salmonella serotypes and non-target microorganisms, most commonly isolated from environmental sources. Furthermore, both methods were applied to experimentally and not experimentally contaminated irrigation water samples. Results confirmed by the ISO culture method, demonstrated the effectiveness of ELIME and RTi-PCR assays to detect a low number of salmonella cells (1-10 CFU/L) reducing drastically the long analysis time usually required to reveal this pathogen.
---
paper_title: Nanoparticle-Based Bio-Bar Codes for the Ultrasensitive Detection of Proteins

paper_content:

An ultrasensitive method for detecting protein analytes has been developed. The system relies on magnetic microparticle probes with antibodies that specifically bind a target of interest [prostate-specific antigen (PSA) in this case] and nanoparticle probes that are encoded with DNA that is unique to the protein target of interest and antibodies that can sandwich the target captured by the microparticle probes. Magnetic separation of the complexed probes and target followed by dehybridization of the oligonucleotides on the nanoparticle probe surface allows the determination of the presence of the target protein by identifying the oligonucleotide sequence released from the nanoparticle probe. Because the nanoparticle probe carries with it a large number of oligonucleotides per protein binding event, there is substantial amplification and PSA can be detected at 30 attomolar concentration. Alternatively, a polymerase chain reaction on the oligonucleotide bar codes can boost the sensitivity to 3 attomolar. Comparable clinically accepted conventional assays for detecting the same target have sensitivity limits of ∼3 picomdar, six orders of magnitude less sensitive than what is observed with this method.
---
paper_title: Electrochemical genosensing of Salmonella, Listeria and Escherichia coli on silica magnetic particles.

paper_content:

A magneto-genosensing approach for the detection of the three most common pathogenic bacteria in food safety, such as Salmonella, Listeria and Escherichia coli is presented. The methodology is based on the detection of the tagged amplified DNA obtained by single-tagging PCR with a set of specific primers for each pathogen, followed by electrochemical magneto-genosensing on silica magnetic particles. A set of primers were selected for the amplification of the invA (278 bp), prfA (217 bp) and eaeA (151 bp) being one of the primers for each set tagged with fluorescein, biotin and digoxigenin coding for Salmonella enterica, Listeria monocytogenes and E. coli, respectively. The single-tagged amplicons were then immobilized on silica MPs based on the nucleic acid-binding properties of silica particles in the presence of the chaotropic agent as guanidinium thiocyanate. The assessment of the silica MPs as a platform for electrochemical magneto-genosensing is described, including the main parameters to selectively attach longer dsDNA fragments instead of shorter ssDNA primers based on their negative charge density of the sugar-phosphate backbone. This approach resulted to be a promising detection tool with sensing features of rapidity and sensitivity very suitable to be implemented on DNA biosensors and microfluidic platforms.
---
paper_title: Iron oxide/gold core/shell nanomagnetic probes and CdS biolabels for amplified electrochemical immunosensing of Salmonella typhimurium.

paper_content:

Abstract There is an imminent need for rapid methods to detect and determine pathogenic bacteria in food products as alternatives to the laborious and time-consuming culture procedures. In this work, an electrochemical immunoassay using iron/gold core/shell nanoparticles (Fe@Au) conjugated with anti- Salmonella antibodies was developed. The chemical synthesis and functionalization of magnetic and gold-coated magnetic nanoparticles is reported. Fe@Au nanoparticles were functionalized with different self-assembled monolayers and characterized using ultraviolet-visible spectrometry, transmission electron microscopy, and voltammetric techniques. The determination of Salmonella typhimurium , on screen-printed carbon electrodes, was performed by square-wave anodic stripping voltammetry through the use of CdS nanocrystals. The calibration curve was established between 1×10 1 and 1×10 6 cells/mL and the limit of detection was 13 cells/mL. The developed method showed that it is possible to determine the bacteria in milk at low concentrations and is suitable for the rapid (less than 1 h) and sensitive detection of S. typhimurium in real samples. Therefore, the developed methodology could contribute to the improvement of the quality control of food samples.
---
paper_title: Rapid Immunosensing ofSalmonellaTyphimurium Using Electrochemical Impedance Spectroscopy: the Effect of Sample Treatment

paper_content:

A label-free immunosensor for rapid detection of Salmonella Typhimurium based on electrochemical impedance spectroscopy was developed. Specific antibody was immobilized to a screen-printed electrode via cysteamine monolayer activated with glutaraldehyde and the impedance was measured between two gold electrodes. Different procedures for sample treatment (combinations of heat and sonication) were tested and their impact on the assay performance was compared. Atomic force microscopy was used to study the effect of the treatment on the cell shape and to confirm the specific binding of Salmonella to the sensing surface. The immunosensor allowed detection of 1×103 CFU ⋅ mL−1 in 20 min with negligible interference from other bacteria. Wide linear response was obtained in the range between 103 CFU ⋅ mL−1 and 108 CFU ⋅ mL−1. The successful detection of Salmonella in spiked milk demonstrates the suitability of sensor for the analysis of real samples.
---
paper_title: A label-free electrochemical impedance immunosensor based on AuNPs/PAMAM-MWCNT-Chi nanocomposite modified glassy carbon electrode for detection of Salmonella typhimurium in milk

paper_content:

Abstract A sensitive and stable label-free electrochemical impedance immunosensor for the detection of Salmonella typhimurium was developed by immobilising anti- Salmonella antibodies onto the gold nanoparticles and poly(amidoamine)-multiwalled carbon nanotubes-chitosan nanocomposite film modified glassy carbon electrode (AuNPs/PAMAM-MWCNT-Chi/GCE). Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to verify the stepwise assembly of the immunosensor. Co-addition of MWCNT, PAMAM and AuNPs greatly enhanced the sensitivity of the immunosensor. The immobilisation of antibodies and the binding of Salmonella cells to the modified electrode increased the electron-transfer resistance ( R et ), which was directly measured with EIS using [Fe(CN) 6 ] 3−/4− as a redox probe. A linear relationship of R et and Salmonella concentration was obtained in the Salmonella concentration range of 1.0 × 10 3 to 1.0 × 10 7 CFU mL −1 with a detection limit of 5.0 × 10 2 CFU mL −1 . Additionally, the proposed method was successfully applied to determine S. typhimurium content in milk samples with satisfactory results.
---
paper_title: Label-free as-grown double wall carbon nanotubes bundles for Salmonella typhimuriumimmunoassay

paper_content:

BACKGROUND ::: A label-free immunosensor from as-grown double wall carbon nanotubes (DW) bundles was developed for detecting Salmonella typhimurium. The immunosensor was fabricated by using the as-grown DW bundles as an electrode material with an anti-Salmonella impregnated on the surface. The immunosensor was electrochemically characterized by cyclic voltammetry. The working potential (100, 200, 300 and 400 mV vs. Ag/AgCl) and the anti-Salmonella concentration (10, 25, 50, 75, and 100 μg/mL) at the electrode were subsequently optimized. Then, chronoamperometry was used with the optimum potential of 100 mV vs. Ag/AgCl) and the optimum impregnated anti-Salmonella of 10 μg/mL to detect S. typhimurium cells (0-10(9) CFU/mL). ::: ::: ::: RESULTS ::: The DW immunosensor exhibited a detection range of 10(2) to 10(7) CFU/mL for the bacteria with a limit of detection of 8.9 CFU/mL according to the IUPAC recommendation. The electrode also showed specificity to S. typhimurium but no current response to Escherichia coli. ::: ::: ::: CONCLUSIONS ::: These findings suggest that the use of a label-free DW immunosensor is promising for detecting S. typhimurium.
---
paper_title: Rapid Evaluation of Salmonella pullorum Contamination in Chicken Based on a Portable Amperometric Sensor

paper_content:

In this study, anti-Salmonella polyclonal antibodies immobilized on cellulose nitrate membrane were used to capture Salmonella pullorum (S. pullorum) in biological samples. The rapid evaluation of S. pullorum contamination was based on the analysis of the activities of catalase, a biomarker of this bacterium. After a screen printed electrode (SPE) modified with multi-wall carbon nanotubes (MWCN)-chitosan-peroxidase was connected to a portable selfmade amperometric sensor, the determination of S. pullorum contamination was carried out by adding the reaction product, which was obtained from the hydrogen peroxide dismutation catalyzed by the bacterial catalase, to the reacting area of the SPEs. A working potential of 0.55 V was applied in the sensing system and the current value displayed on the amperometric sensor was used as the detection signal. This method allowed the quantification of S. pullorum with the detection limit of 100cfu mL-1 in culture media and chicken samples. The stability, reproducibility and sensitivity of the modified SPE were also investigated. Moreover, successive analysis was conveniently accomplished by replacing the one-off SPE. This portable sensing system is a rapid, cost-effective and straightforward approach for screening S. pullorum contamination in food samples.
---
paper_title: Novel surface antigen based impedimetric immunosensor for detection of Salmonella typhimurium in water and juice samples.

paper_content:

A specific surface antigen, OmpD has been reported first time as a surface biomarker in the development of selective and sensitive immunosensor for detecting Salmonella typhimurium species. The OmpD surface antigen extraction was done from Salmonella typhimurium serovars, under the optimized growth conditions for its expression. Anti-OmpD antibodies were generated and used as detector probe in immunoassay format on graphene-graphene oxide (G-GO) modified screen printed carbon electrodes. The water samples were spiked with standard Salmonella typhimurium cells, and detection was done by measuring the change in impedimetric response of developed immunosensor to know the concentration of serovar Salmonella typhimurium. The developed immunosensor was able to specifically detect S. typhimurium in spiked water and juice samples with a sensitivity upto 10(1)CFUmL(-1), with high selectivity and very low cross-reactivity with other strains. This is the first report on the detection of Salmonella typhimurum species using a specific biomarker, OmpD. The developed technique could be very useful for the detection of nontyphoidal Salmonellosis and is also important from an epidemiological point of view.
---
paper_title: A label-free electrochemical DNA biosensor based on covalent immobilization of salmonella DNA sequences on the nanoporous glassy carbon electrode

paper_content:

Abstract Herein, an easy and cost-effective approach to the immobilization of probe was performed. The amino modified salmonella ssDNA probe sequence was covalently linked with carboxylic group on the surface of nanoporous glassy carbon electrode to prepare the DNA biosensor. The differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) techniques were used for the determination of salmonella DNA in the concentration ranges of 10–400 pM and 1–400 pM with limits of detection of 2.1 pM and 0.15 pM, respectively.
---
paper_title: An electrochemical genosensor for Salmonella typhi on gold nanoparticles-mercaptosilane modified screen printed electrode.

paper_content:

In this work, we fabricated a system of integrated self-assembled layer of organosilane 3-mercaptopropyltrimethoxy silane (MPTS) on the screen printed electrode (SPE) and electrochemically deposited gold nanoparticle for Salmonella typhi detection employing Vi gene as a molecular marker. Thiolated DNA probe was immobilized on a gold nanoparticle (AuNP) modified SPE for DNA hybridization assay using methylene blue as redox (electroactive) hybridization indicator, and signal was monitored by differential pulse voltammetry (DPV) method. The modified SPE was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and atomic force microscopy (AFM) method. The DNA biosensor showed excellent performances with high sensitivity and good selectivity. The current response was linear with the target sequence concentrations ranging from 1.0 × 10(-11) to 0.5 × 10(-8)M and the detection limit was found to be 50 (± 2.1)pM. The DNA biosensor showed good discrimination ability to the one-base, two-base and three-base mismatched sequences. The fabricated genosensor could also be regenerated easily and reused for three to four times for further hybridization studies.
---
paper_title: Disposable DNA biosensor based on thin-film gold electrodes for selective Salmonella detection

paper_content:

Abstract The development of a disposable electrochemical biosensor for selective Salmonella detection in presence of other pathogens is described. The device is based on thin-film gold electrodes and is fabricated employing standard microsystems technology. The method involves the immobilization of a thiolated capture probe able to hybridize with its complementary sequence (target). The hybridization event is detected using the ruthenium complex, [Ru(NH 3 ) 5 L ] 2+ , where L is [3-(2-phenanthren-9-yl-vinyl)-pyridine] as electrochemical indicator. The combination of MEMS technology to fabricate electrodes with a predetermined configuration and the use of a hybridization redox indicator which interacts preferentially with dsDNA gear to the development of an approach that not only quantifies complementary target sequence, but also is selective to Salmonella in presence of other pathogens, which can act as potential interferents. In base of these results, a multianalyte detection platform including Salmonella , Lysteria and Escherichia coli has been developed.
---
paper_title: Recent Advances in Bacteriophage Based Biosensors for Food-Borne Pathogen Detection

paper_content:

Foodborne diseases are a major health concern that can have severe impact on society and can add tremendous financial burden to our health care systems. Rapid early detection of food contamination is therefore relevant for the containment of food-borne pathogens. Conventional pathogen detection methods, such as microbiological and biochemical identification are time-consuming and laborious, while immunological or nucleic acid-based techniques require extensive sample preparation and are not amenable to miniaturization for on-site detection. Biosensors have shown tremendous promise to overcome these limitations and are being aggressively studied to provide rapid, reliable and sensitive detection platforms for such applications. Novel biological recognition elements are studied to improve the selectivity and facilitate integration on the transduction platform for sensitive detection. Bacteriophages are one such unique biological entity that show excellent host selectivity and have been actively used as recognition probes for pathogen detection. This review summarizes the extensive literature search on the application of bacteriophages (and recently their receptor binding proteins) as probes for sensitive and selective detection of foodborne pathogens, and critically outlines their advantages and disadvantages over other recognition elements.
---
paper_title: Pathogen detection using engineered bacteriophages

paper_content:

Bacteriophages, or phages, are bacterial viruses that can infect a broad or narrow range of host organisms. Knowing the host range of a phage allows it to be exploited in targeting various pathogens. Applying phages for the identification of microorganisms related to food and waterborne pathogens and pathogens of clinical significance to humans and animals has a long history, and there has to some extent been a recent revival in these applications as phages have become more extensively integrated into novel detection, identification, and monitoring technologies. Biotechnological and genetic engineering strategies applied to phages are responsible for some of these new methods, but even natural unmodified phages are widely applicable when paired with appropriate innovative detector platforms. This review highlights the use of phages as pathogen detector interfaces to provide the reader with an up-to-date inventory of phage-based biodetection strategies.
---
paper_title: Phagomagnetic Separation and Electrochemical Magneto-Genosensing of Pathogenic Bacteria

paper_content:

This paper addresses the use of bacteriophages immobilized on magnetic particles for the biorecognition of the pathogenic bacteria, followed by electrochemical magneto-genosensing of the bacteria. The P22 bacteriophage specific to Salmonella (serotypes A, B, and D1) is used as a model. The bacteria are captured and preconcentrated by the bacteriophage-modified magnetic particles through the host interaction with high specificity and efficiency. DNA amplification of the captured bacteria is then performed by double-tagging polymerase chain reaction (PCR). Further detection of the double-tagged amplicon is achieved by electrochemical magneto-genosensing. The strategy is able to detect in 4 h as low as 3 CFU mL(-1) of Salmonella in Luria-Bertani (LB) media. This approach is compared with conventional culture methods and PCR-based assay, as well as with immunological screening assays for bacteria detection, highlighting the outstanding stability and cost-efficient and animal-free production of bacteriophages as biorecognition element in biosensing devices.
---
paper_title: Application of bacteriophages in sensor development

paper_content:

Bacteriophage-based bioassays are a promising alternative to traditional antibody-based immunoassays. Bacteriophages, shortened to phages, can be easily conjugated or genetically engineered. Phages are robust, ubiquitous in nature, and harmless to humans. Notably, phages do not usually require inoculation and killing of animals; and thus, the production of phages is simple and economical. In recent years, phage-based biosensors have been developed featuring excellent robustness, sensitivity, and selectivity in combination with the ease of integration into transduction devices. This review provides a critical overview of phage-based bioassays and biosensors developed in the last few years using different interrogation methods such as colorimetric, enzymatic, fluorescence, surface plasmon resonance, quartz crystal microbalance, magnetoelastic, Raman, or electrochemical techniques.
---
paper_title: A label-free electrochemical DNA biosensor based on covalent immobilization of salmonella DNA sequences on the nanoporous glassy carbon electrode

paper_content:

Abstract Herein, an easy and cost-effective approach to the immobilization of probe was performed. The amino modified salmonella ssDNA probe sequence was covalently linked with carboxylic group on the surface of nanoporous glassy carbon electrode to prepare the DNA biosensor. The differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) techniques were used for the determination of salmonella DNA in the concentration ranges of 10–400 pM and 1–400 pM with limits of detection of 2.1 pM and 0.15 pM, respectively.
---
paper_title: Disposable DNA biosensor based on thin-film gold electrodes for selective Salmonella detection

paper_content:

Abstract The development of a disposable electrochemical biosensor for selective Salmonella detection in presence of other pathogens is described. The device is based on thin-film gold electrodes and is fabricated employing standard microsystems technology. The method involves the immobilization of a thiolated capture probe able to hybridize with its complementary sequence (target). The hybridization event is detected using the ruthenium complex, [Ru(NH 3 ) 5 L ] 2+ , where L is [3-(2-phenanthren-9-yl-vinyl)-pyridine] as electrochemical indicator. The combination of MEMS technology to fabricate electrodes with a predetermined configuration and the use of a hybridization redox indicator which interacts preferentially with dsDNA gear to the development of an approach that not only quantifies complementary target sequence, but also is selective to Salmonella in presence of other pathogens, which can act as potential interferents. In base of these results, a multianalyte detection platform including Salmonella , Lysteria and Escherichia coli has been developed.
---
paper_title: Electrochemical immunosensors for Salmonella detection in food

paper_content:

Pathogen detection is a critical point for the identification and the prevention of problems related to food safety. Failures at detecting contaminations in food may cause outbreaks with drastic consequences to public health. In spite of the real need for obtaining analytical results in the shortest time possible, conventional methods may take several days to produce a diagnosis. Salmonella spp. is the major cause of foodborne diseases worldwide and its absence is a requirement of the health authorities. Biosensors are bioelectronic devices, comprising bioreceptor molecules and transducer elements, able to detect analytes (chemical and/or biological species) rapidly and quantitatively. Electrochemical immunosensors use antibody molecules as bioreceptors and an electrochemical transducer. These devices have been widely used for pathogen detection at low cost. There are four main techniques for electrochemical immunosensors: amperometric, impedimetric, conductometric, and potentiometric. Almost all types of immunosensors are applicable to Salmonella detection. This article reviews the developments and the applications of electrochemical immunosensors for Salmonella detection, particularly the advantages of each specific technique. Immunosensors serve as exciting alternatives to conventional methods, allowing "real-time" and multiple analyses that are essential characteristics for pathogen detection and much desired in health and safety control in the food industry.
---
paper_title: Rapid and sensitive detection of Salmonella Typhimurium on eggshells by using wireless biosensors.

paper_content:

This article presents rapid, sensitive, direct detection of Salmonella Typhimurium on eggshells by using wireless magnetoelastic (ME) biosensors. The biosensor consists of a freestanding, strip-shaped ME resonator as the signal transducer and the E2 phage as the biomolecular recognition element that selectively binds with Salmonella Typhimurium. This ME biosensor is a type of mass-sensitive biosensor that can be wirelessly actuated into mechanical resonance by an externally applied time-varying magnetic field. When the biosensor binds with Salmonella Typhimurium, the mass of the sensor increases, resulting in a decrease in the sensor's resonant frequency. Multiple E2 phage–coated biosensors (measurement sensors) were placed on eggshells spiked with Salmonella Typhimurium of various concentrations (1.6 to 1.6 × 107 CFU/cm2). Control sensors without phage were also used to compensate for environmental effects and nonspecific binding. After 20 min in a humidity-controlled chamber (95%) to allow binding of th...
---
paper_title: Sequential detection of Salmonella typhimurium and Bacillus anthracis spores using magnetoelastic biosensors.

paper_content:

Multiple phage-based magnetoelastic (ME) biosensors were simultaneously monitored for the detection of different biological pathogens that were sequentially introduced to the measurement system. The biosensors were formed by immobilizing phage and 1 mg/ml BSA (blocking agent) onto the magnetoelastic resonator’s surface. The detection system included a reference sensor as a control, an E2 phage-coated sensor specific to S. typhimurium, and a JRB7 phage-coated sensor specific to B. anthracis spores. The sensors were free standing during the test, being held in place by a magnetic field. Upon sequential exposure to single pathogenic solutions, only the biosensor coated with the corresponding specific phage responded. As the cells/spores were captured by the specific phage-coated sensor, the mass of the sensor increased, resulting in a decrease in the sensor’s resonance frequency. Additionally, non-specific binding was effectively eliminated by BSA blocking and was verified by the reference sensor, which showed no frequency shift. Scanning electron microscopy was used to visually verify the interaction of each biosensor with its target analyte. The results demonstrate that multiple magnetoelastic sensors may be simultaneously monitored to detect specifically targeted pathogenic species with good selectivity. This research is the first stage of an ongoing effort to simultaneously detect the presence of multiple pathogens in a complex analyte.
---
paper_title: Phagomagnetic Separation and Electrochemical Magneto-Genosensing of Pathogenic Bacteria

paper_content:

This paper addresses the use of bacteriophages immobilized on magnetic particles for the biorecognition of the pathogenic bacteria, followed by electrochemical magneto-genosensing of the bacteria. The P22 bacteriophage specific to Salmonella (serotypes A, B, and D1) is used as a model. The bacteria are captured and preconcentrated by the bacteriophage-modified magnetic particles through the host interaction with high specificity and efficiency. DNA amplification of the captured bacteria is then performed by double-tagging polymerase chain reaction (PCR). Further detection of the double-tagged amplicon is achieved by electrochemical magneto-genosensing. The strategy is able to detect in 4 h as low as 3 CFU mL(-1) of Salmonella in Luria-Bertani (LB) media. This approach is compared with conventional culture methods and PCR-based assay, as well as with immunological screening assays for bacteria detection, highlighting the outstanding stability and cost-efficient and animal-free production of bacteriophages as biorecognition element in biosensing devices.
---
paper_title: Electrochemical immunoassay for Salmonella Typhimurium based on magnetically collected Ag-enhanced DNA biobarcode labels

paper_content:

We describe a sensitive electrochemical immunoassay for Salmonella enterica serovar Typhimurium, a common foodborne pathogen which can cause infection at extremely small doses. The assay is based on the recognition of DNA biobarcode labels by differential pulse anodic stripping voltammetry (DPASV), following Ag enhancement. The biobarcodes consist of latex spheres (mean diameter 506 nm ± 22 nm) modified by ferromagnetic Fe3O4 particles. Each biobarcode is loaded by adsorption with approx. 27 molecules of mouse monoclonal antibody against S. Typhimurium and 3.5 × 10(5) molecules of 12 mer ssDNA. The assay is performed by adding the biobarcode, S. Typhimurium cells, and biotin-conjugated rabbit polyclonal antibody against Salmonella into well plates. After antigen-antibody binding, magnetic collection enables the excess polyclonal antibody to be washed off. Exposure to avidin-coated screen printed electrodes, and formation of the avidin-biotin bond, then enables the excess biobarcode to be removed. The biobarcode remaining on the electrode is quantified by DPASV measurement of Ag(+) ions following catalytic Ag deposition. The assay showed a negligible response to 10(7) CFU mL(-1)E. coli and had a limit of detection of 12 CFU mL(-1) in buffer, and 13 to 26 CFU mL(-1) for heat-killed and whole cell S. Typhimurium in plain milk, green bean sprouts and raw eggs. To the best of our knowledge, this is the lowest reported limit of detection for Salmonella by an electrochemical immunoassay not requiring sample pre-enrichment.
---
paper_title: Electrochemical Aptasensor for Rapid and Sensitive Determination of Salmonella Based on Target-Induced Strand Displacement and Gold Nanoparticle Amplification

paper_content:

ABSTRACTA simple, rapid, and sensitive electrochemical aptasensor based on target-induced strand displacement and gold nanoparticle amplification was developed for the determination of Salmonella. The aptamer for Salmonella was captured on the sensing interface by hybridizing with a capture probe. In the presence of Salmonella, the aptamer dissociated from the capture probe as the stronger interaction between the aptamer and the Salmonella. The single-strand capture probe was then hybridized with the biotinylated detection probe assembled on gold nanoparticles and catalyzed by streptavidin–alkaline phosphatase, providing a sensitive electrochemical response. The gold nanoparticles significantly amplified the detection probe signal and increased the sensitivity. The linear dynamic range was from 2 × 101 to 2 × 106 CFU mL−1 with a detection limit of 20 CFU mL−1. This strategy was utilized for the determination of Salmonella in milk, demonstrating potential application in clinical diagnostics, food safety, a...
---
paper_title: Diazonium-based impedimetric aptasensor for the rapid label-free detection of Salmonella typhimurium in food sample.

paper_content:

Fast and accurate detection of microorganisms is of key importance in clinical analysis and in food and water quality monitoring. Salmonella typhimurium is responsible for about a third of all cases of foodborne diseases and consequently, its fast detection is of great importance for ensuring the safety of foodstuffs. We report the development of a label-free impedimetric aptamer-based biosensor for S. typhimurium detection. The aptamer biosensor was fabricated by grafting a diazonium-supporting layer onto screen-printed carbon electrodes (SPEs), via electrochemical or chemical approaches, followed by chemical immobilisation of aminated-aptamer. FTIR-ATR, contact angle and electrochemical measurements were used to monitor the fabrication process. Results showed that electrochemical immobilisation of the diazonium-grafting layer allowed the formation of a denser aptamer layer, which resulted in higher sensitivity. The developed aptamer-biosensor responded linearly, on a logarithm scale, over the concentration range 1 × 10(1) to 1 × 10(8)CFU mL(-1), with a limit of quantification (LOQ) of 1 × 10(1) CFU mL(-1) and a limit of detection (LOD) of 6 CFU mL(-1). Selectivity studies showed that the aptamer biosensor could discriminate S. typhimurium from 6 other model bacteria strains. Finally, recovery studies demonstrated its suitability for the detection of S. typhimurium in spiked (1 × 10(2), 1 × 10(4) and 1 × 10(6) CFU mL(-1)) apple juice samples.
---

Title: Electrochemical Biosensors for Rapid Detection of Foodborne Salmonella: A Critical Overview

Section 1: Introduction
Description 1: Introduce the significance of Salmonella detection in food products, the limitations of conventional methods, and the need for rapid and sensitive detection techniques.

Section 2: Nano-and Micro-Sized Materials for Improving Detection
Description 2: Discuss the various nano and micro-sized materials used to enhance the performance of biosensors for Salmonella detection.

Section 3: Electrochemical Immunosensors for Salmonella Detection
Description 3: Describe the principles, formats, and examples of electrochemical immunosensors used for Salmonella detection.

Section 4: GNPs
Description 4: Provide detailed examples and performances of electrochemical immunosensors using gold nanoparticles (GNPs).

Section 5: MBs
Description 5: Discuss the use of magnetic beads (MBs) in the development of electrochemical immunosensors for Salmonella detection.

Section 6: QDs
Description 6: Cover the application of quantum dots (QDs) in electrochemical immunosensors for the detection of foodborne Salmonella.

Section 7: Label-Free Electrochemical Immunosensors
Description 7: Explain the concept and examples of label-free electrochemical immunosensors for detecting Salmonella.

Section 8: CNTs
Description 8: Detail the use of carbon nanotubes (CNTs) in enhancing the sensitivity and performance of electrochemical immunosensors for Salmonella.

Section 9: Electrochemical Genosensors, Phagosensors, and Aptasensors for Salmonella Detection
Description 9: Introduce and elaborate on the various electrochemical platforms like genosensors, phagosensors, and aptasensors used for Salmonella detection.

Section 10: Genosensors
Description 10: Discuss the principles, methods, and examples of electrochemical genosensors for Salmonella detection.

Section 11: Phagosensors
Description 11: Describe the use of bacteriophages in electrochemical biosensing for the detection of Salmonella.

Section 12: Aptasensors
Description 12: Explain the application and advantages of aptamer-based electrochemical sensors in Salmonella detection.

Section 13: Conclusions
Description 13: Summarize the findings, emphasize the importance of developing rapid and sensitive detection methods, and outline the challenges and future perspectives in the field.