THIEVES who leave faint fingerprints on plastic banknotes or photographs in newspapers could find themselves fingered by a technique that shows up previously undetectable prints.

The most sensitive methods for detecting fingerprints involve either dusting a surface with fluorescent powder, which sticks to the oily residue left by the pattern of ridges on the skin, or using a chemical that reacts with the print to produce a fluorescent image. This surface is then photographed through an optical filter that blocks all but the fluorescent light to produce an image of the print. But some materials, such as certain newspaper inks and plastics, emit light at the same frequency as the fluorescent powder. This makes the pattern difficult to distinguish.

Now a team in Australia has found it can do a better job with a device known as a chemical imaging spectrometer. It is commonly used in the pharmaceutical industry for ...