Fingerprinting technique enjoys notable success

日期:2019-03-03 01:05:08 作者:浦驿筅 阅读:

By Anna Gosline Dirty cash is a criminal’s dream, as it is almost impossible for the police to lift fingerprints from certain well-used banknotes. But now a technique can reveal who has handled Australian banknotes, which, because they are made from polymer, are notoriously difficult to lift prints from. The technique is so good that it makes previously invisible prints left on a range of surfaces clear for all to see. A fresh fingerprint is easy to spot because it leaves a moist residue of fatty acids, amino acids and proteins, which dusting powder readily sticks to. Older, drier prints can usually be made to show up if fumed with cyanoacrylate superglue, which reacts with the organic compounds in the prints to form a white polymer along the ridges and whorls. But this will not work on notes with flourescent, coloured and patterned surfaces, such as an Australian $5 note, even with the help of dyes or optimal lighting. The problem, says Chris Lennard of the Australian Federal Police in Canberra, is that existing techniques rely on visible light to create contrast between prints and their background. So Lennard, along with Mark Tahtouh and his colleagues at the University of Technology in Sydney, turned to a form of infrared imaging. In tests, they laid down prints on the $5 bill and developed them with superglue. The prints were invisible to the naked eye and white-light photography. They then scanned the notes using Fourier transform infrared spectroscopy (FTIR), which records the characteristic spectra produced by chemical compounds as they absorb and emit infrared light. By feeding information from the FTIR to a standard software package they were able to reconstruct the image of the fingerprint even on difficult regions of the banknote, including those left on the fingerprint-like swirls of the queen’s hair. Antonio Cantu at the US Secret Service in Washington DC says he is keen to incorporate the technique into his own chemical imaging system, which till now has relied on visible light. But he also points out that the FTIR is not suitable for scanning large areas to look for prints. “You actually have to know where to look beforehand,” he says. One way round this would be to run a preliminary scan at low resolution to gain a glimmer of a print, and then zero in with a high-resolution scan to resolve it in detail. The technique would also be useful when traditional imaging uncovers the traces of a print,