THE sweaty, greasy residue that forms a fingerprint might one day reveal the
identity of a criminal as surely as the pattern of whorls and ridges.
Whenever we touch something, we leave behind a minute residue of proteins,
salts and fatty acids. Because the exact proportions of these components vary
between individuals, some forensic scientists suspect that a chemical
fingerprint could be as unique as a physical one.
Getting information from such tiny samples can be tricky. But a team led by
Dale Perry of the Lawrence Berkeley National Laboratory in California told the
American Chemical Society meeting in Chicago last week that they can analyse
samples of sweat less than 10 micrometres across—smaller than a single
fingerprint ridge.
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While powerful, their technique has a practical hitch—it needs a
synchrotron, a huge particle accelerator that produces extremely intense light
beams. When a thin infrared beam is shone at the sample, the wavelengths that
are absorbed reveal its chemical make-up.
No one yet knows whether the chemical profile of our sweat is truly unique.
One 1999 study by Gary Mong of the Pacific Northwest National Laboratory in
Richland, Washington, showed that each of 79 test subjects had different sweat
profiles when their prints were examined using gas chromatography. “We have a
hunch that they can at least be segregated by age and by sex,” Mong says. His
method required a couple of fingerprints’ worth of sweat and destroyed the
prints in the process.
Perry says his method is hundreds of times as sensitive and doesn’t affect
the prints, leaving them for other forensic scientists to study. So far Perry
and his team have analysed three prints from people in their lab. He says more
work is needed to find out how much information can be extracted from a chemical
print.
Sweat profiles could even reveal when the print was made, since the
characteristic chemicals evaporate or break down at different rates when exposed
to air. “That’s just speculation for the moment, but it’s very exciting,” says
team member Wayne McKinney.
Stephen Homeyer of the FBI’s Forensic Science Research Unit in Quantico,
Virginia, agrees that sweat profiles could have their uses. But he’s not
convinced that chemicals can pin down identity, especially since prints can be
affected by what people have been touching. “I don’t know if you’d ever get past
the issue of environmental contamination,” says Homeyer. In any event, he adds,
“I don’t know of any forensics lab that has a synchrotron in the backyard.”