Forensic Science and Fingerprints

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 PurdueUniversity, 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 molecule¹s
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.

‘It¹s 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 company¹s 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. “That¹s 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 collaborates, 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. ”It¹s just one more test,” Dr. Cooks said, “and it can reveal a whole lot of detail.”

The New York Times
August 8, 2008
Fingerprint Test Shows Not Only Who but What
By KENNETH CHANGCopyright 2008 The New York Times Company