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Analytical scientists from Loughborough University have demonstrated for the first time that drug residue—namely the fast-acting sleeping pill Zolpidem that has been linked to drug-facilitated sexual assault and drink spiking—can be detected on gel-lifted fingerprints.

Jim Reynolds and Ayoung Kim say the breakthrough could shed new light on cold cases and unsolved crimes since forensic gel lifters—which transfer prints onto a gelatine surface—are used globally by crime scene officers to preserve and visualize fingerprints.

“This is the first time that analysis of gel-lifted prints for a drug substance has been accomplished and shows that lifted prints and other forensic marks can be useful information,” said lead researcher Reynolds. “Since gel-lifted prints and marks can be stored for many years, the technique could be of real use in cold cases where additional information may prove useful to either link or exonerate a suspect to the investigation. Working with police forces and applying the method to cold case samples could help bring criminals to justice who may have thought they have got away with it.”

There are currently a number of tests that can detect drugs directly from fingerprints but they face limitations—they can be destructive to the fingerprint, degrade drug residues and are negatively affected by environmental interferences.

It has long been speculated that gel-lifted prints contain valuable chemical information and could offer more accurate drug detection.

However, traditional techniques used to analyze the chemicals present in a sample have previously not been suitable for gel lifters. This is because they detect all chemicals present, including those that make up the gel, making it difficult to identify specific substances.

The method used by Reynolds and Kim—called sfPESI-MS—overcomes this issue using a rapid separation mechanism that distinguishes the drug substance from the background of the gel.

The process involves sampling the chemicals from the gel lifters into tiny liquid droplets. The chemicals extracted into the droplets are then ionized. The drug substance chemicals are more surface active than the chemicals originating from the gel, which enables them to be separated from the mixture. This separation method enables the direct detection of a drug substance using mass spectrometry.

“By linking chemical information to the fingerprint, we can identify the individual and link them to the handling of an illicit substance, which may prove useful in a prosecution,” said Reynolds. “This could also be useful in detecting individuals who have been spiking drinks. For example, if the drug they are using gets onto their fingertips, they will leave evidence at the scene.”