New fingerprint method can spot drugs or explosives

Police now have the ability to analyse the traces of cannabis, cocaine and other drugs, or explosives, in a fingerprint itself.

The new technique reveals, in extraordinary detail, the chemical compounds that make up the print and could also find medical uses, since tiny traces of chemicals at our fingertips could signal the presence of a disease or an illness.

This method can also be used directly on a fingerprint, right where it's found, without the need to lift the print off and take it to a lab for analysis.

Dr Demian Ifa, Prof Graham Cooks at Purdue University in West Lafayette, and colleagues report in the journal Science how they used a technique called desorption electrospray ionization, or DESI, which involves spraying a solvent onto a fingerprinted surface and then analysing the droplets that scatter off the print with a method called mass spectroscopy.

"The classic example of a fingerprint is an ink imprint showing the unique swirls and loops used for identification, but fingerprints also leave behind a unique distribution of molecular compounds," Prof Cooks said. "Some of the residues left behind are from naturally occurring compounds in the skin and some are from other surfaces or materials a person has touched."

In this way, the researchers can detect minute traces of compounds - marked as dots on the print - that were on the fingertips of the person who left the print.

This technique can pick up small amounts of drugs like cocaine or THC, the active ingredient from marijuana, as well as compounds from explosives.