Device can reveal what you touched

Mass spectrometry used to pick up traces of substances carried on fingerprints

August 08, 2008|By New York Times News Service

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

It can also identify what the person has been touching - drugs, explosives or poisons, for example.

Writing in today's issue of the journal Science, Dr. 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 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.

In Cooks' method, a tiny spray of liquid that has been electrically charged - either water or water and alcohol - is sprayed on a bit of the fingerprint.

The droplets dissolve compounds in the fingerprints and splash them off the surface into the analyzer. The liquid is heated and evaporates, and the electrical charge is transferred to the fingerprint molecules, which are then identified by 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 such as glass, paper and plastic. The researchers then analyzed 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.

"That's an advantage that this technique would have," said Dr. Bruce Goldberger, a 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 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 has begun selling such analyzers as add-ons to large laboratory mass spectrometers, which cost several hundred thousand dollars each.

The technology could eventually have important medical applications.

If a Desi analyzer can be miniaturized and automated into a surgical tool, a surgeon could, for example, quickly test body tissues for the presence of molecules associated with cancer.

As it becomes cheaper and more widely available, the Desi technology has potential ethical implications, Cooks said.

Instead of drug tests, a company could surreptitiously check for illegal drug use among its employees by analyzing computer keyboards after the workers have gone home, for instance.

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