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.

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 analyzer. 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.