Researchers in the UK have developed a technique which can reveal within seconds if someone has been taking cocaine.
The method could pave the way for a simple new test for the illegal Class A drug.
The researchers, from the University of Surrey, developed a way of analysing traces of chemical cocaine in fingerprints.
When someone has taken the drug, traces of two "marker" chemicals, benzoylecgonine and methylecgonine, are excreted from the skin.
The chemicals are present in fingerprint residue, and can be detected even when a person is tested after washing their hands.
The researchers used a chemical analysis method called 'paper spray mass spectrometry' to identify the cocaine markers in fingerprints from patients seeking treatment at drug rehabilitation centres.
The method proved to be 99% effective at detecting cocaine use among the patients.
Dr Melanie Bailey, who co-led the study, said: "This is a real breakthrough in our work to bring a real time, non-invasive drug-testing method to the market that will provide a definitive result in a matter of minutes."
She added: "We are already working on a 30 second method.
"It is non-invasive, hygienic and can't be faked. By the nature of the test, the identity of the subject, and their drug use, is all captured within the sample itself."
The team anticipates that the technique could be adopted by law enforcement agencies within the next decade.