US scientists have used infrared (IR) spectroscopy to distinguish between overlapping fingerprints and reveal their chemical history.

IR imaging reveals traces of explosive (red) on a fingerprint

Ira Levin and colleagues, at the National Institutes of Health, Bethesda, claim the technique can identify latent (invisible) fingerprints containing contaminants, such as drugs or explosives, and filter out overlapping fingerprints originating from the natural secretions found in fingertips. Previous IR studies of fingerprints have been based only on natural secretions, says Levin, and so failed to provide this extra forensic evidence.

The group took an IR spectroscopic image of two overlapping fingerprints - one natural fingerprint and one containing an explosive. They then distinguished the contaminated fingerprint's spectral image from the overlapping print using a mathematical method called multivariate analysis. The resulting image clearly showed the explosive in between the ridges of the fingerprint. 'You can obtain a fingerprint with the associated forensic evidence which can go through MI5 or FBI databases to target an individual,' explains Levin.

Claude Roux, director of the Centre for Forensic Science at the University of Technology, Sydney, Australia, comments that although this is not the first research to be done in this area, it is 'interesting and very relevant because it combines two major aspects of forensic investigations: human identification and chemical characterisation. It shows that not only can IR spectroscopic imaging identify controlled substances, such as explosives, but it can also link these chemicals with the person who touched them.'

Levin says works needs to be done to make the technique more easily accessible but he is confident that it will be useful to forensic teams worldwide.

Jane Hordern

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