New tech reveals most hidden finger-prints

Scientists have developed a novel technique that can detect hidden fingerprints in a crime scene.

The new way of visualising fingerprints from crime scenes, using colour-changing fluorescent films, could lead to higher confidence identifications from latent (hidden) fingerprints on knives, guns, bullet casings and other metal surfaces.

The odds of two individuals having identical fingerprints are 64 billion to 1, making them an ideal tool for identification in criminal investigations, researchers said.

The greatest source of fingerprint forensic evidence comes from latent fingerprints, ie those not immediately visible to the eye, because they are less likely to be 'wiped'.

However, visualising these prints with sufficient clarity for positive identification often proves difficult. Despite the availability of several enhancement techniques, only 10 per cent of fingerprints taken from crime scenes are of sufficient quality to be used in court.

Researchers from the University of Leicester have been working on a new technique that visualises fingerprints by exploiting their electrically insulating characteristics.

The fingerprint material acts like a mask or stencil, blocking an electric current that is used to deposit a coloured electro-active film. This directs the coloured film to the regions of bare surface between the fingerprint deposits, thereby creating a negative image of the print.

Unlike conventional fingerprint visualisation reagents, the polymers used by researchers are electrochromic, that is to say they change from one colour to another when subjected to an electrical voltage.

The technique is highly sensitive as even tiny amounts of insulating residue, just a few nanometres thick, can prevent polymer deposition on the metal below.

As a result, much less fingerprint residue is required than is typical for other techniques. Also, because it focuses on the gaps between the fingerprint deposits, it can be used in combination with existing (eg powder-based) approaches.

In their latest paper in Faraday Discussions the team, led by Professor Robert Hillman, have developed this technique further by incorporating within the film fluorophore molecules that re-emit light of a third colour when exposed to light or any other form of electromagnetic radiation such as ultra-violet rays.

Their success in combining the electrochromic and fluorescence approaches provides a significantly wider palette to 'colour' their films and two sets of 'levers' in the form of electricity and light to control and tune this colouration in order to achieve the best possible contrast with the underlying metal surface.