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  • Fighting crime with mass spectrometry

Photonics Spectra
Oct 2008
Laura Marshall,

WEST LAFAYETTE, Ind. – It’s tough to live a life of crime these days. Burglar alarms are fancier, locks have gone biometric, and surveillance cameras get smaller and sneakier all the time. And now, thanks to researchers at Purdue University, the criminal life has gotten even tougher.

Purdue analytical chemistry professor R. Graham Cooks and his team have created a tool that can determine not only the identity of a suspect but also what that suspect has recently handled, be it cocaine, gunpowder or any other incriminating substance.

The process is called Desi, which is short for “desorption electrospray ionization,” but the tool itself isn’t new. “Desi’s from a few years ago,” Cooks pointed out. It involves spritzing a surface with electrically charged droplets, which transfer their charges to the sample’s molecules, ionizing them. The molecules are collected into a standard mass spectrometer, “and after that, it’s really a case of simple mass spectrometry,” Cooks said. The molecules are analyzed, and their chemical makeup is determined.


Researchers at Purdue University say that their mass spectrometry method, which involves desorption electrospray ionizationmass, can be used to obtain a wider range of information about fingerprints than traditional dusting does. The fingerprint on the left is a computer-generated image created from cocaine analysis for use in identification software. The print on the right shows an image created from an analysis of the presence of cocaine molecules. The figure on the right shows the mass spectrum acquired from a single pixel and highlights the presence of cocaine. Reprinted with permission of Purdue University.

Using Desi to fight crime – that’s what’s new

The researchers found that the method has some big advantages over traditional fingerprinting. They discovered that they were able to identify trace substances on subjects’ fingertips just by analyzing their prints. If a subject had handled something before leaving a fingerprint, chemical residue from that substance would be left behind as part of the print.

They also were able to differentiate between two separate sets of prints when one was layered on top of the other, just by determining their individual chemical “signatures.” This has piqued the interest of law enforcement experts. “That’s something we’ve always been challenged by,” said Leonard Butt, a forensic scientist for the Maryland State Police in Pikesville, specializing in latent prints.

Still another advantage is the ability to do all this without “dusting” – covering the prints in powder and rendering them completely useless for further compositional testing. “Mass spectrometry is a destructive technique,” said postdoctoral researcher Demian R. Ifa, who was the lead author of the team’s paper for the Aug. 8, 2008, issue of Science. “However, it is not 100 percent destructive.

After a Desi imaging experiment, if it is still necessary – since chemical information was already collected – the remaining material from the surface can be further extracted and analyzed by conventional techniques.”

Best of all, the Desi method could be accessible to crime labs very soon, according to Prosolia Inc., an Indianapolis company that has licensed the technology for sale.

“Prosolia sells an ionization source that uses the Desi application that is capable of doing imaging applications such as this,” said company president Kevin Boscacci. “[That device] is attached to commercially available mass spectrometers.”

The device someday could be taken out of the laboratory and into the field.

Prosolia is working with Griffin Analytical Technologies of West Lafayette to develop a portable instrument. Until then, “mass specs already exist in labs, and this is an add-on to it, and that would not be cost-prohibitive,” said Boscacci, who estimated that the add-on would run in the $50,000 to $60,000 range.

“I don’t think that mass spectrometry is being used as much in the law enforcement field as possible, or at least that’s our understanding,” he added. “And so, since mass specs are kind of the gold standard in chemical detection, anything that brings a new level of sophistication into another area is going to take hold with time.”

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