Fingerprint Test Shows Not Only Who but What

Source: nytimes.com

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 known as mass spectrometry could find a wider application in crime investigations.

The equipment to perform such tests is already commercially available, although expensive. Smaller, cheaper, portable versions are probably only a couple of years away.

In mass spectrometry, an electrical charge is added to a molecule, which is then accelerated by an electric field. The molecule enters a magnetic field, causing its trajectory to bend. The amount of bending tells the molecule’s mass-to-electric charge ratio. That is usually enough information to deduce what molecule it is.

In Dr. Cooks’ method, a tiny spray of electrically charged liquid – either water or water and alcohol – is sprayed on a tiny bit of the fingerprint. The droplets dissolve compounds in the fingerprints and splashes them off the surface into the analyzer. The liquid evaporates, and the electrical charge is transferred to the fingerprint molecules, which are then identified through mass spectrometry.

“It’s just that simple,” Dr. Cooks said. 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 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 on the surface, but literally showed a pattern of cocaine in the shape of the fingerprint, leaving no doubt who had left the cocaine behind.

Prosolia, Inc., a small company in Indianapolis, has licensed the Desi technology from Purdue and is already selling such analyzers as add-ons to large laboratory mass spectrometers, which cost several hundred thousand dollars each.

Prosolia has so far sold “40 or so” of its analyzers, said Peter T. Kissinger, the company’s chairman and chief executive. The most sophisticated version that would be needed for the fingerprint analysis went on sale only this year.

The fingerprint work “is a nice, quick dramatic indication of what the possibilities are,” Dr. Kissinger said.

However, fingerprints are not its main focus for Prosolia or Dr. Cooks. “This is really just an offshoot of a project that is really aimed at trying to develop a methodology ultimately to be used in surgery.” Dr. Cooks said.

If a Desi analyzer can be miniaturized and automated into a surgical tool, a surgeon could, for example, quickly test for the presence of molecules associated with cancer. “That’s the long-term aim of this work,” Dr. Cooks said.

In unpublished research, the researchers have tested the method with bladder tumors in dogs.

Prosolia is collaborating with Griffin Analytical Technologies, a subsidiary of ICx collaboraties, on a Desi analyzer that works with a portable mass spectrometer. That product is probably a year or two away from mark, Dr. Kissinger said.

As it becomes cheaper and more widely available, the Desi technology has potential ethical implications, Dr. Cooks said. Instead of drug tests, a company could surreptitiously check for illegal drug use of its employees by analyzing computer keyboards after the employees have gone home, for instance.

“It’s just one more test,” Dr. Cooks said, “and it can reveal a whole lot of detail.”