X rays detect fingerprints

From San Diego, at a meeting of the American Chemical Society

Collecting fingerprints at a crime scene may look easy on television shows, but in real life, it’s often challenging. Fingerprints left on textiles, wood, leather, and surfaces with multicolored backgrounds are often difficult to discern. To catch these elusive prints, researchers at Los Alamos (N.M.) National Laboratory have developed a method that visualizes fingerprints with X rays.

Analytical chemist Chris Worley and his colleagues use a process called micro-X-ray fluorescence to detect minute quantities of chlorine, potassium, and sodium—elements commonly found in sweat. Those elements are transferred to a surface from the ridges in a person’s fingers.

To visualize the chemical patterns, the Los Alamos researchers irradiate a surface with a small beam of X rays. The three target substances absorb the radiation and reemit X rays of different energies. The instrument collects the data and converts them into a digital image.

Along with sweat, fingerprints contain an oily substance called sebum and, in some cases, skin cells. In traditional detection techniques, spray-on powders, liquids, or vapors bind to sebum and color fingerprints, permanently altering them. But the X-ray technique leaves prints intact, says Worley. As a result, forensic scientists could subsequently extract additional evidence, such as DNA, from fingerprints. The process could also be used to analyze other chemicals in prints. A high concentration of sulfur, for instance, might suggest exposure to gunpowder.

Worley doesn’t expect the technology to replace traditional methods. Not all prints contain enough detectable material to produce an image, he says. What’s more, samples would have to be transported to a crime lab for analysis because the prototype device is large. Worley plans to develop a portable X-ray device that can catch prints at the scene of the crime.

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