Scientists use infrared lasers to lift fingerprints from crime scenes. (Credit: Louisiana State University)

Fingerprints left behind at a crime scene are not only a unique identifier—they are also a palette that can show a bit about the suspect’s activities, including traces of gunpowder, explosives or even condom lubricants.

Various disciplines have attempted to better understand the chemistry in those deposits of oils and proteins, sweat and touch DNA.

The latest two-step method would involve laser ablation, vacuum capture and mass spectrometry—a technique especially effective on porous surfaces like cardboard, according to Louisiana State University chemists.

“The most challenging part was trying to determine a method of collection that lost the least amount of sample and wouldn’t destroy the surface it was on,” said Eden Camp, a graduate chemistry student who came up with the idea after an internship with the Louisiana State Police two summers ago.

“We realized that if our techniques work for biomolecules as fragile as DNA and RNA, it should work with almost anything,” said Fabrizio Donnarumma, a postdoctoral researcher. “We can capture almost anything that is on a surface. In this case, it just happened to be fingermarks.”

The team reports its findings in a recent issue of The Journal of the American Society of Mass Spectrometry.

Laser ablation is the first step of the process. The laser is focused on water molecules and moisture on a surface, causing the chemical bonds to vibrate and then essentially explode. Gas is created, which lifts molecules like DNA off the surface.

The vacuum pulls the gas and all the molecules into a small filter. The captured material is then assessed with mass spectrometry (another option available at this point would be a gas chromatography-mass spectrometer).

The study reports capturing caffeine at levels as small as 1 nanogram, along with traces of condom lubricants, antibacterial peptides from antiseptic cream, and explosives. The subject test materials included glass, plastic, aluminum and cardboard.

The team envisions a portable laser system for fingerprints in the future, depending on funding.

Kermit Murray, the chemistry professor heading the LSU laboratory, said the forensic applications are clear.

“We have been using infrared lasers for many years to ablate biomolecules from tissue samples for mass spectrometry, so we know that they are very efficient,” said Murray.

The LSU scientists are not the only team looking to real-time applications of lasers at crime scenes. Igor Lednev and his team of chemists at University at Albany have been working on analysis through Raman spectroscopy—and they envision telling a whole range of personal identifiers from stains at crime scenes, among other forensic traces. The Albany work has been featured in Forensic Magazine over the last year.