Fingerprint can reveal what you’ve touched

With a new analytical technique, a fingerprint can now reveal much more than the identity of a person.

With a new analytical technique, a fingerprint can now reveal much more than the identity of a person. It can now also identify what the person has been touching: drugs, explosives or poisons, for example.

Writing in Friday’s issue of the journal Science, R Graham Cooks, a professor of chemistry at Purdue University, and his colleagues describe how a laboratory technique, mass spectrometry, could find a wider application in crime investigations.

The equipment to perform such tests is already commercially available, although prohibitively expensive for all but the largest crime laboratories. Smaller, cheaper, portable versions

of such analyzers are probably only a couple of years away.

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In Dr Cooks’s method, a tiny spray of liquid that has been electrically charged, either water or water and alcohol, is sprayed on a tiny bit of the fingerprint. The droplets dissolve compounds in the fingerprints and splash them off the surface into the analyser. The liquid is heated and evaporates, and the electrical charge is transferred to the fingerprint molecules, which are then identified by a device called a mass spectrometer. The process is repeated over the entire fingerprint, producing a two-dimensional image.

The researchers call the technique desorption electrospray ionization, or Desi, for short.

In the experiments described in the Science paper, solutions containing tiny amounts of various chemicals including cocaine and the explosive RDX were applied to the fingertips of volunteers. The volunteers touched surfaces like glass, paper and plastic. The researchers then analysed the fingerprints.

Because the spatial resolution is on the order of the width of a human hair, the Desi technique did not just detect the presence of, for instance, cocaine, but literally showed a pattern of cocaine in the shape of the fingerprint, leaving no doubt who had left the cocaine behind.

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“That’s an advantage that this technique would have,” said Bruce Goldberger, professor and director of toxicology at the University of Florida who runs a forensics laboratory that helps medical examiners and law enforcement. Goldberger was not involved in the research.

The chemical signature could also help crime investigators tease out one fingerprint out of the smudges of many overlapping prints if the person had been exposed to a specific chemical, said Demian R Ifa, a postdoctoral researcher and the lead author of the Science paper.

Prosolia Inc, a small company in Indianapolis, has licensed the Desi technology from Purdue and is already selling such analysers as add-ons to large laboratory mass spectrometers,

which cost several hundred thousand dollars each.