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It’s red, it’s blue: new colour boosts forensic fingerprint detection

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Forensic investigators may soon be able to use a new, more effective and low-cost method of detecting latent (invisible) fingerprints, thanks to recent discoveries by a team of forensic science researchers at Curtin University.

Previous industry research revealed the compound Nile Red combined exceptionally well with lipids present in latent fingerprints, providing a vibrant, photoluminescent (glowing) fingerprint that can be seen under special lighting.

But the Nile Red reagent is highly expensive and its use poses health and safety issues, which led Curtin researchers to experiment with a similar compound, Nile Blue A.

Professor Simon Lewis from the University’s Department of Chemistry said small quantities of Nile Red form naturally when Nile Blue A is dissolved in water.

“Using Nile Red on its own isn’t practical, given it costs about $654 per gram and is prepared by dissolving it in methanol, a toxic solvent,” Professor Lewis said.

“On the other hand, Nile Blue A is extremely cost effective at $6 per gram, widely available, easily transportable, well-established in the scientific industry to stain lipids and can be used safely in the field as it dissolves in water.

“What we found was that the Nile Blue A itself and the small quantities of Nile Red produced in solution interacted with both skin secretions and surfaces to provide a photoluminescent fingerprint on a blue background.”

This discovery may have enormous positive implications for organisations such as the WA Police and Australian Federal Police, whose staff use forensic techniques on a daily basis to collect physical evidence such as latent fingerprints from crime scenes all over Australia.

The research focused on developing prints on porous surfaces, such as paper, and researchers then found this technique could also be applied to identify fingerprints on paper that has been wet.

Curtin provides specialist forensic training to the WA Police and had a member of the Australian Federal Police on the research team.

The experience of a practising professional was vital in determining potential applications of the discovery.

“One area of research focused on using the Nile Blue solution to develop usable fingerprints on non-porous surfaces, such as plastics, and from sticky surfaces, such as electrical and duct tape,” Professor Lewis said.

“These research results will also be extremely useful when trying to solve crimes that involve paper-based evidence.”
Further research is required to test the full effectiveness of the Nile Blue solution before the technique can be applied in the field.

The additional research will include testing on latent prints left on a greater variety of surfaces, on prints left by a wider variety of donors, on paper that has been in liquid for a long period of time and on fingerprints that have been on surfaces for a long period of time and may have degraded.

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