Reported December 2006

BACKGROUND: Scientists at Los Alamos National Laboratory have developed a new fingerprint visualization technique using X-rays that leaves prints intact and reveals chemical markers that could give investigators new clues for tracking criminals and missing persons. Traditional fingerprinting methods involve treating samples with powders, liquids, or vapors to add color to the print, so it can easily be photographed. This process is known as contrast enhancement. However, dusting for fingerprints can sometimes alter the prints, erasing valuable forensic clues. Children's fingerprints are especially difficult to detect.

HOW MXRF WORKS: The new technique uses a process called micro-X-ray fluorescence (MXRF), which rapidly reveals the elemental composition of a sample by shining a thin beam of X-rays onto it without disturbing the sample. All chemical elements emit and absorb radiation at a "signature" frequency of light. For instance, sodium emits primarily orange light, while oxygen (used in neon lights) emits green light. Scientists can pass collected light through an instrument called a spectrograph to spread it into a spectrum, much like visible light spreads into a rainbow of colors by a prism. By carefully studying how the spectrum becomes brighter or darker at each wavelength, scientists can tell what chemical elements are present in a given sample.

WHAT THEY FOUND: The researchers used MXRF to detect the sodium, potassium and chlorine from salts excreted in human sweat -- which is sometimes present in detectable quantities in fingerprints. Since those salts are deposited along the ridge patterns in a fingerprint, it is possible to use the elemental analysis to produce a visual image of that fingerprint for analysis. It is especially useful for tracking down lost or missing children -- The new method can detect prints based on chemical markers left behind in the child's fingerprints due to the presence of food, soil or saliva, and this information can be used to track down evidence of the child's movements.

ABOUT X-RAYS: Like visible light, X-rays are wavelike forms of electromagnetic energy (light) carried by tiny particles called photons. The only difference is the higher energy level of the individual photons, and the corresponding shorter wavelength of the rays, which make them undetectable by the human eye. X-ray photons have energies that range from hundreds to thousands of times higher than those of visible photons. X-ray machines image the outline of bones and organs, while a CT scan machine forms a full 3-D computer model of the inside of a patient's body. Doctors can even examine the body one narrow slice at a time. The X-ray beam moves all around the patient, scanning from hundreds of different angles, and the computer takes all that information to compile a 3-D image of the body.

If you would like more information, please contact:

Christopher G. Worley, Ph.D.
Actinide Analytical Chemistry
Los Alamos National Laboratory
Los Alamos, New Mexico
(505) 667-2934
cworley@lanl.gov