Fingerprints from polymer fiver

C&I Issue 7, 2016

In September 2016, the first £5 banknotes made from polymer will hit UK consumer’s wallets.
Now, researchers at Loughborough University, UK, have shown how fresh fingermarks can be lifted from the new plastic currency – a vital capability in the event of fraud, robbery, drugs crime or counterfeiting. 

First, the researchers use vacuum metal deposition (VMD) to heat and vaporise copper and deposit a thin layer of metal atoms, around 0.2 to 3nm thick, onto the polymer surface (Forensic Science International, doi: 10.1016/j.forsciint.2016.05.037). The copper piles up fairly evenly if the note is clean, but becomes much more chaotic once it hits the water and oily milieu of a fingerprint. Light shone on the polymer via a halogen light was imaged using an infrared filter, allowing an investigator to see the prints.

In a further step, the researchers report that a forensic gelatine sheet can be applied on top of the copper atoms and then lifted and the gel sprayed with rubeanic acid so that the fingerprints can be seen by naked eye. Rubeanic acid reacts with the copper to produce a new compound, and a visually distinctive fingermark. 

‘We have shown previously that all sorts of information can be retrieved from a surface using those gels,’ says Paul Kelly, an inorganic chemist at Loughborough. ‘You would be taking other stuff off the note as well, some of which might be useful from a forensic point of view, such as traces of drugs or explosives.’

His lab is now developing protocols for others to use the fingerprinting technique on new polymer notes.   

Senior lecturer in forensics at the University of Leicester, UK, John Bond, describes the technique as innovative, with promising results. ‘But they now need to test it on aged prints, where there is less sweat present and where consecutive deposits are left,’ he says. ‘This is more like what you would find at a real crime scene.’

Additionally, ‘VMD has been used for a number of years with gold and zinc to recover fingerprints on smooth non-porous surfaces, such a plastic bags, but it never had widespread use because of the cost of the equipment.’ says Bond, who worked for Northamptonshire Police for nearly 20 years as head of forensics. 

VMD could yield better quality fingerprints from polymer banknotes than other techniques, but Bond suspects its use would be restricted to serious crime investigations. 

A competitor technique developed by Roberto King – also an author on the current paper – at forensic equipment manufacturer Foster + Freeman, works by using infrared fluorescent powder, which should be less expensive than VMD.

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