Novel process lifts fingerprints based on geometry, not chemistry
By Ben Coxworth
May 18, 2010
If shows like CSI have taught us anything about lifting fingerprints, it’s that we do it by dusting them with powder or fuming them with chemicals... and that we have to turn on blue accent lighting and play moody electronic music while we’re doing it. Approaches like these rely on chemical reactions with the deposited finger skin oil to provide the print. A new method developed at Penn State University, however, lets the physical geometry of the print do the talking. The oils are left unaltered, which could make all the difference in a criminal investigation.
The process is called conformal-evaporated-film-by-rotation, and was originally developed to create highly-detailed copies of biological surfaces such as insect eyes or butterfly wings. It utilizes a form of physical vapor deposition where materials are heated in a vacuum, causing them to vaporize and then condense on the surface of an object rotating above them, covering that object in a thin film.
In the case of Penn State’s technique, the materials that they heated were magnesium flouride and chalcogenide glass, which is a combination of germanium, antimony and selenium. The film created was only about one micron thick, but that was enough to essentially “amplify” the ridges and valleys of fingerprints, allowing analysts to read them with an optical device.
One of the big advantages of the new technique is that it doesn’t change the chemistry of the skin oils, so they can still be analyzed after the prints have been lifted. "The body chemistry of the person who left the fingerprint can tell us some things," said Penn State researcher Robert Shaler. "If the suspect is older or younger or a lactating mother, for example." It could also be used to retrieve fingerprints from bomb fragments, while still leaving the chemistry of the explosive residue unchanged.
So far the technique can only be performed in a laboratory setting, but the researchers are working on making the technology portable, so it could be used in the field. They also plan on applying it to other types of evidence, such as footprints, bite marks and lip impressions.
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