Laser Ablation/Vacuum Boosts Fingerprint Analysis

Using IR laser ablation coupled with vacuum capture, a system of fingermark sampling has been developed that could be used for traditional fingerprint analysis and also to capture, filter and analyze biomolecules and trace substances such as DNA or explosives.

Scientists use infrared lasers to lift fingerprints from crime scenes. Courtesy of Louisiana State University.

A team at Louisiana State University performed laser ablation at 3 µm in reflection mode with subsequent capture of the ejecta with a filter connected to a vacuum. The laser heated up any moisture present within the surface area, lifting biomolecules such as DNA off the surface.

After the laser ablated, a small vacuum pump system was used to pull the moisture and all molecules associated with it into a thimble-sized filter. The researchers flushed the contents of the filter into an analysis device to determine the mass of any compounds or molecules in the sample.

The technique was successfully tested on diverse materials, including glass, plastic, aluminum and cardboard — a material whose porosity makes substances from fingermarks difficult to capture.

For testing purposes, the fingermarks were laced with substances as varied as caffeine, Neosporin antiseptic cream, condom lubricants and TNT. Using matrix assisted laser desorption ionization (MALDI), researchers showed that it was possible to detect caffeine after spiking fingerprints with amounts as low as 1 ng. Detection of explosives from fingermarks left on plastic surfaces, as well as from direct deposition on the same surface using gas chromatography mass spectrometry (GC-MS), was shown.

LSU researchers Fabrizio Donnarumma and Fan Cao set up an infrared laser system used to remove fingermark materials from a surface for chemical analysis. Courtesy of Paige Jarreau.

In the future, this technology could be used to help forensic bomb squads find and deactivate bombs without needing to send squad members into dangerous areas, while potentially at the same time capturing and identifying any genetic material also present at the site.

“Let's say I was preparing a bomb and I wasn't using gloves. If I touched the bomb and then touched a surface, my fingermarks might leave behind trace amounts of an explosive,” said LSU researcher Fabrizio Donnarumma. “Using this technique, forensic teams could lift those compounds off a surface, for example with a portable laser system or, better yet, a portable laser system transported by a robot, and send the samples into a lab for analysis and identification.”

The team is developing optical fiber attachments for their laser system that would allow for a portable laser fingermark-capturing system to sample various surfaces in the field.

“A laser beam is a straight line,” Donnarumma said. “It can be difficult to focus a traditional laser system at a precise point, especially on an uneven surface. But if you run that laser through a flexible optical fiber, similar to how a fiber optic cable works, you can sample a wider variety of surfaces more easily.”

The researchers are pursuing a patent for the technology, and are collaborating with companies and law enforcement offices to develop better techniques for analyzing the chemical signatures of fingermarks at crime scenes.

The research was published in the Journal of The American Society of Mass Spectrometry (doi:10.1007/s13361-017-1703-2).