Forensic breakthrough: drugs detected on gel-lifted fingerprints

Analytical scientists from Loughborough University have demonstrated for the first time that drug residue — namely the fast-acting sleeping pill Zolpidem, which has been linked to drug-facilitated sexual assault and drink spiking — can be detected on gel-lifted fingerprints. The breakthrough could shed new light on unsolved crimes, as forensic gel lifters — which transfer prints onto a gelatine surface — are used globally to preserve and visualise fingerprints found at crime scenes.

A number of tests can detect drugs directly from fingerprints, but these can be destructive to the fingerprint, degrade drug residues or be affected by environmental interference. 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 analyse the chemicals present in a sample have previously not been suitable for gel lifters as they detect all chemicals present — including those that make up the gel. The method used at Loughborough University, 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 ionised, which means they gain or lose electric charge depending on their chemical properties. 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, which identifies chemicals by measuring their molecular weight.

The Loughborough researchers successfully tested the technique using Zolpidem-laced fingerprints lifted from glass, metal and paper surfaces in a laboratory setting, with their results published in the journal Drug Testing and Analysis. They now hope to work with police forces to analyse stored gel-lifted prints and use the method to identify other substances.

“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 interrogated for useful information,” said Dr Jim Reynolds, the research lead.

“Zolpidem was the focus of our research, but the method could just as easily be applied to other drug substances a person may have been handling and could be applied to other chemicals such as explosives, gunshot residues, paints and dyes.

“By linking chemical information to the fingerprint, we can identify the individual and link to the handling of an illicit substance, which may prove useful in a prosecution.”

First author Dr Ayoung Kim said the researchers would like to apply their method to real samples from criminal investigations, with Reynolds adding, “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.”

Image credit: iStock.com/Rosendo Serrano Valera