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Scientists say they can tell if someone has been taking drugs by analysing their fingerprint.

The team at the University of Surrey showed that chemicals produced when cocaine is broken down in the body could be detected in the fingerprint.

They argue the test could be useful in prisons, drug abuse clinics and even for routine testing in the workplace.

However, the current kit may be impractical as it is both the size of a washing machine and very expensive.

Drug-testing normally relies on a fluid sample such as blood, urine or saliva.

However, the researchers believe the fingerprint method would be quicker, less invasive and much harder to fake as the donor's identity would be contained in the fingerprint.

Chemical search

Their study, published in the journal Analyst, hunts for two chemicals benzoylecgonine and methylecgonine.

They are produced when cocaine is broken down by the body, however, they can be released in tiny quantities in sweat.

These chemicals would be left on the paper used to take the fingerprint.

A sample of the fingerprint is then analysed by a mass spectrometer, which detects chemicals based on their atomic size.

The team showed they could produce the same results as a conventional blood test.

Dr Melanie Bailey, a lecturer in analytical and forensic science, told the BBC: "The mass spectrometer is the same size as a washing machine and what we are currently using is £400,000 to buy so it is not cheap."

She said there are cheaper products on the market which raise the "exciting possibility that it is a test you could make portable one day".

Useful?

Dr Bailey added: "I would have thought it useful for workplace testing, somewhere where you want high-throughput."

Workplace drug screening is already used in some industries, particular those where safety is key such as operating heavy machinery or driving.

"Drug rehabilitation centres where we are working are keen to use this methodology for patients on drug-treatment programmes.

"Then there are customs and probation services, drug testing and perhaps roadside testing."