Investigators were once satisfied when a fingerprint matched a replica in a database. Yet who knew that there was much more these prints could tell us — secrets that were only revealed until we looked deeper into the microscope at the level of a nanoparticle?

Traditional methods of enhancing fingerprints utilise fine powders and a soft brush, which are applied to the greasy spots where a suspect has touched a smooth object. Generally, the raised ridges of fingertips also transfer organic fluids like sweat and body oils that build up between the ridges and are left behind on any surface touched by that finger. These oils attract the powders and enhance the image for collection and identification by investigators.

Smooth surfaces like walls and car doors support easily processed prints. Still, prints left on porous surfaces like paper or skin are particularly difficult to process, even with the vapours of super glues in a closed container. It is estimated that more than half of the fingermarks left on papers cannot be enhanced and identified by traditional methods.

For these challenging prints, Israeli researchers applied gold nanoparticles to paper containing possible fingerprints. These nanoparticles were coated by a special formulation in order to stick to paper — not fingerprint residue. In other words, they were designed to be repelled by the traces of sweat and body oils that had been soaking into the porous surface. At this point, the fingerprint is still invisible. By applying a developing solution containing silver (like in photographic film developing), the silver is attracted to the gold nanoparticles and reveals an inverse image of the print that can be seen by a normal eye and processing equipment.


Invisible prints revealed 

Researchers in Switzerland have determined that the attraction of nanoparticles to fingerprints is not electrostatic, as previously thought, but chemical. Fingerprints actually leave a complex compound of chemicals from the oils, sweat and other organic materials that transfer with the print.

The nanoparticles form a chemical bond between the carboxyl group and an amine group present in the amino acids and proteins that make up the fingermark residue. This chemical bond is sensitive to what compounds are in the amino acids.


Identification of chemicals consumed

Nanoparticles can reveal information by binding with the metabolites in the sweat left with the fingerprint. Metabolites are breakdown products of the consumption of nicotine and other drugs such as cocaine, marijuana, prescription drugs, methamphetamine, crack and alcohol. When the microscopic antibodies recognise the metabolite, they change colours in the resulting trace, and essentially allow the fingerprints to not only identify the user, but also deduce elements of a user’s lifestyle.


Reading rainbows from a strange brew

Bruce McCord of the FBI Forensic Science Center developed a process where a mixture of gold nanoparticles is mixed with the victim’s urine and then illuminated by laser. He then reads the analysis of the signal emitted. This has been particularly successful in discovering benzodiazepines, also known as date rape drugs, which fade fast after application and up until now have been difficult to detect in body fluid samples after a few days. The mingling traces in the urine are measured at the nanogram-per-ml concentration. By analysing the spectrum of the emitted light allows detection of a variety of drugs.


Enhancing DNA Analysis

The primary procedures of DNA sequencing are now more portable and faster, thanks to nanotechnology. McCord recently released a genotyping system that involves a procedure that previously took 2 days or more to analyse in a lab by one that can provide identification in only 25 minutes.

Based on an invention that delves into the nanoparticles immersed in a microfluidic solution within a small device made by Agilent Technologies in Florida, the machine can recognise the origin of the organic sample (saliva, blood, semen, skin or an organ) and measure 13 locations in the genome specific to that individual.

It is assumed that once these microfluidic devices become common in police departments, it will be possible to check to see if the suspect’s DNA is in a database or matches a crime scene sample in the time that suspect is being booked into a holding cell. Another important advantage of retreating difficult fingerprints from old, unsolved cases is that the amino acids have a very long half-life, and analysing old prints can help solve these cold cases.


Advancing Forensic Techniques

While fingerprints and DNA are not new forensic techniques, these new nanotechnologies supercharge the process, and extend the ability of analysis to expand detection and elaborate on new discoveries from the same evidence.

Your turn: Are you aware of any novel technologies that will make forensic science more reliable, more accessible and more exact? Tell us in the comments below. We love to hear from our readers!



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