As most crime scene experts know, dusting for fingerprints can sometimes destroy parts of the prints, erasing potentially valuable forensic clues.
Conventional fingerprinting methods involve treating samples with powders, liquids or vapors to add color to the fingerprint so it can be easily photographed, a process called contrast enhancement.
But fingerprints left on many substances such as fibrous papers, textiles, wood, leather, plastic, multi-colored backgrounds and human skin can sometimes be difficult to detect this way. Plus, children's fingerprints are often more difficult to detect than adult prints due to the absence of an oily substance called sebum and the presence of other fatty acid deposits unique only to children.
Any improvements in detection techniques that can be forensically useful are welcome, and a group of government chemists believe they have an answer.
Researchers at the Los Alamos National Laboratory in New Mexico say they have developed a novel means of detecting fingerprints using X-rays that don't disturb the print in any way. The technique also is able to reveal chemical markers that could give investigators new clues for tracking suspects and missing persons.
The technique uses a process called microbeam X-ray fluorescence (MXRF), which rapidly reveals the elemental composition of a sample by irradiating it with a thin beam of X-rays without disturbing the sample.
This method is important because it does not require using developing agents to treat the print.
"We collect an image of a print pattern intact without altering its composition," says Christopher Worley, an analytical chemist at Los Alamos.
The research, however, has stalled at an unforeseen snag. The researchers have run out of money.
"The research is currently at a standstill awaiting additional funding," Worley says. "So far, we have not been able to find anyone interested, willing and able to provide funding to pursue the idea further."
So far the research is proof-of-concept only, to demonstrate the possibility of detecting fingerprint patterns using MXRF, whereby the fingerprint pattern is determined by detecting inorganic elements present in the print residue.
"Thus, we both detect the print pattern digitally and collect chemical information from the print as well," Worley says.
Fingerprints contain detectable quantities of salts, such as sodium chloride and potassium chloride, excreted in sweat. The Los Alamos researchers have shown they could detect the sodium, potassium and chlorine from these salts. Since these salts are deposited along the patterns present in a fingerprint, an image of the fingerprint can be visualized producing an elemental image for analysis.
Worley says the technique is another tool to be used in an attempt to visualize a print that might be difficult to detect with current powder or chemical treatment methods. He stresses that MXRF work is proof-of-concept only.
"We are not claiming we have a method to replace current protocols," he says. Rather, Worley believes this method compliments current techniques.
"While this method currently requires a prior knowledge of the print location, it clearly has some advantages over contrast-based techniques for special cases," he says.
For example, a print left from a finger coated with a residue such as gunpowder might be detectable from the sulfur and potassium content. Other distinctive fingerprint examples, such as those containing lotion, sunscreen, saliva or certain food residue, can be detected by MXRF based on inorganic elemental constituents.
"Because MXRF is a spectroscopic method, the elemental composition of a fingerprint is examined, and visual contrast with the substrate is irrelevant," Worley says.
Thus, if sufficient detectable residue is present, the print can be identified regardless of the background color.