GOTCHATraces of cocaine delineate a fingerprint left on glass. By bouncing water droplets off a surface, chemists can image fingerprints and sniff out thousands of different chemicals simultaneously.D.R. Ifa et al./Science

Fingerprints can tell a lot more about people — what they’ve touched, what they’ve eaten, what drugs they’ve taken — than just their identities. Now, a new analytic tool could make it easier to spot terrorists and to diagnose diseases from telltale chemical markers, but could also pose new privacy risks.

The method, described in the Aug. 8 Science, can map a fingerprint based on the presence of virtually any water-soluble chemical. “It’s the difference between a black-and-white picture and a full-color picture,” says chemist Graham Cooks of Purdue University in West Lafayette, Ind.

Cooks and his colleagues singled out traces of chemicals, such as the high-power explosive RDX, cocaine and THC, marijuana’s main active ingredient.

The researchers used a technique called DESI, pioneered by him and his collaborators in 2004. In DESI, researchers spray microscopic droplets of water onto a sample. The first droplets that hit the sample form a film that dissolves chemicals on the sample’s surface. When additional droplets splash onto the liquid film, some droplets bounce back and are sucked into a tube.

There, the droplets are heated to isolate the chemicals, which usually break into smaller molecules. Finally, the device performs the traditional technique of mass spectrometry, which identifies molecules according to their molecular weight.

Researchers mapped the fingerprints by using the device to scan individual spots — each one-fifth of a millimeter wide — one at a time.

Mass spectrometers, Cooks says, are among the most sensitive and precise tools available to the chemist. “When they really need answers in CSI — they put things in the mass spec,” he adds.

But traditional mass spectrometry requires samples to be analyzed in a vacuum, while DESI can be used in the field and on any surface.

“DESI is extremely powerful and promising,” says Facundo Fernandez, a chemist at the Georgia Institute of Technology in Atlanta. “It gives a ton of information.”

Cooks says DESI could also be tested as a tool for medical diagnosis. In principle, fingerprints could contain chemicals, not found through blood or urine tests, that indicate the presence of a disease.

DESI is not the first technique that’s been used for finding chemicals in fingerprints. Recently, researchers have experimented with a technique that analyzes chemicals by scanning them with a laser (SN 8/2/08, p. 22).

Also, last year, Sergei Kazarian of Imperial College London and his collaborators showed how they could do that by bouncing infrared rays off an object. The infrared method is faster, doesn’t damage the sample and doesn’t require knowing in advance where a fingerprint is likely to be, Kazarian points out.

Cooks says the effectiveness of the two techniques should be compared in blind tests. “This is where we need to have a shoot-off at the O.K. Corral.”

Meanwhile, if such chemical analytic tools become available as consumer gadgets, anyone — employers, spouses, school principals — could potentially discover details just by pointing their DESI pen at fingerprints on somebody’s paper cup. “This is a major concern,” Cooks says. “The implications for privacy are written all over this.”

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