Chemical residue analysed for gender, diet and other agents.

A fingerprinting technique, which lifts chemical residue as well as the print, could reveal the gender and diet of a suspect and show if they have had contact with other substances, such as gunshot residue, explosives, narcotics or biological agents.

Details of the technique, developed by a team of researchers at Imperial College London’s Department of Chemical Engineering, led by Professor Sergei Kazarian, have been published in the latest edition of the Analytical Chemistry journal.

Chemical residues contain a few millionths of a gram of fluid and can be found on all fingerprints. Conventional fingerprinting techniques often distort or destroy this chemical information, but Imperial's scientists found that commercial gelatine-based tape provides a simple method for collection and transportation of prints for chemical imaging analysis.

Once lifted, the prints are analysed in a spectroscopic microscope. The sample is irradiated with infra-red rays to identify individual molecules within the print to give a detailed chemical composition.

The information is then processed by an infra-red array detector, originally developed by the US military in smart missile technology. The array detector chemically maps the residue. This process builds up a picture, or chemical photograph.

"The combined operational advantages and benefits for forensic scientists of tape lifting prints and spectroscopic imaging really maximises the amount of information one can obtain from fingerprints,” said Professor Kazarian. "Our trials show that this technique could play a significant role in the fight against crime."

Furthermore, by observing the composition of chemicals present in a print, forensic scientists could also determine the age of a crime scene from which prints were lifted.

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