Fingerprints from a crime scene are useless if the perpetrator鈥檚 prints are not on file. But new forensic techniques now mean they can be used to determine whether a person is a smoker, uses drugs, and even which aftershave they wear 鈥� information that could help narrow down suspects.
Fingerprints contain a mixture of skin cells, sweat secretions and substances picked up from elsewhere. Careful analysis can show whether a person may have handled drugs or explosives, but the new tools make it possible to determine a person鈥檚 habits from the secretions in their prints as well.
鈥淲e have found you can detect cotinine, made when someone metabolises nicotine, in fingerprints,鈥� says Sue Jickells, an analytical chemist at Kings College London, UK. 鈥淭his tells you if that person is a smoker, and this kind of additional information could be useful if you don鈥檛 have a suspect.鈥�
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Jickells plans to collect prints from addicts at heroin and crack cocaine clinics to see if these drugs can be detected in fingerprints residue too. And she has shown that traces of cosmetics can be found left behind in prints. 鈥淚n one sample we picked up some hair product that was eventually linked back to one of our students,鈥� she says.
Fat fingerprint
For about five hours after application, aftershave is also left behind, she says. 鈥淚t is currently difficult to differentiate different kinds of product,鈥� Jickells adds. 鈥淏ut I think in the future biosensors will be used to easily tell them apart.鈥�
Jickells is also looking at differences in individual fingerprint chemistry. Much of the material of a fingerprint consists of lipids 鈥� fat secreted by pores in the skin.
鈥淚t seems people differ in the amount they secrete of the different kinds of lipid,鈥� Jickells says. 鈥淭he differences aren鈥檛 great enough to be able to identify someone specifically, but you could definitely rule out suspects if you found they had produced a lot of one lipid, in contrast to a print at the crime scene.鈥�
Nanoparticle tags
A particularly quick method of analysing fingerprints has been developed by David Russell, a chemist at the University of East Anglia, UK, who has also developed a way to tell if a fingerprint was left by a smoker.
Russell coated gold nanoparticles with an antibody specific to cotinine, and labelled the particles with a fluorescent protein. A solution containing the particles is then applied to a fingerprint and illuminated with light.
The fluorescent particles then show up under the light if the print is from a smoker. 鈥淭he idea is to develop something for first responders, so they can quickly find out more about a suspect,鈥� Russell says.
Russell鈥檚 nanoparticle method has also been used to develop a quick check for toxins like ricin and cholera. Particles are coated with a sugar that binds to the toxins and dissolved in a coloured solution. If a sample containing the toxin is added to the solution, the particles immediately clump together and scatter light differently. This causes the solution to quickly change colour. 鈥淚t鈥檚 a simple, quick, yes-or-no detection method,鈥� Russell says.
Russell鈥檚 team hopes to adapt the technique to speed up detection of the H5N1 strain of avian influenza, or bird flu. Currently, samples must be sent away for lab analysis, so a portable detector could see potential outbreaks confirmed rapidly in the field.
