Narrowing pool by sweat

ALBANY, N.Y. _ Sweat cools us down while simultaneously embarrassing us with foul odors and armpit stains. But sweat can also help forensic scientists determine people's gender.

Jan Halamek, a professor and researcher at the University at Albany, has discovered a way to analyze the secretions to identify the gender and number of people at a crime scene. The research, published in Analytical Chemistry in March, follows his past work that analyzed fingerprints and then blood to identify gender.

"I'm doing biochemistry, which studies what is missing in the forensic portfolio," Halamek said. "We developed very sensitive and selective biochemical assays to analyze molecules from the body fluids."

Along with a team of graduate and undergraduate student researchers, Halamek analyzed the concentrations of three metabolic compounds found in traces of sweat: lactate, urea and glutamate.

"What was the clearest spin off is if you have two males, two females, yes their metabolic levels may be similar but they are not identical," Halamek said.

Since the biochemical content of sweat is mainly dependent on age, gender and activity level, the chances of two people having the exact same levels of all three metabolites are zero, Halamek said. This was reported in the recently published study, which found that 25 mimicked and 25 authentic sweat samples were easily distinguishable upon analysis.

A year ago, Halamek's team developed a strip _ which is not commercially available _ that can pick up any sweat sample with a simple swipe on a surface. It's an important development because sweat is difficult to find at a crime scene.

"Blood is easy, blood is red," he said. "With no system to find sweat samples, there's no point having a system to analyze them."

All that is needed is half a droplet of sweat to be able to perform the analysis, which takes a few minutes, Halamek said. DNA evidence can take months to analyze.

With this development, forensic scientists could narrow the pool of suspects present at crime scenes. Eventually, Halamek's team wants to develop a database of metabolic profiles _ similar to the fingerprint database _ to be able to identify individuals from sweat samples. It will be difficult though because metabolite levels are also dependent on varying factors like diet, sleep, exercise and age, he said.

"You cannot necessarily link my sweat sample today (to one) from a week ago _ my metabolism will change," Halamek said. "We are a very dynamic system, but there is a pattern recognition software. Record me for a day and you will find my system has a unique pattern, unique ratios, and it clips in."

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