Fingerprints have been used since the 1800s to conclusively identify the individual who made the prints. David Russell (University of East Anglia, United Kingdom) and coworkers have expanded the utility of fingerprints by detecting residual illicit narcotic molecules left behind in the prints.
Principles of detection.
The scientists wanted to ensure that the narcotic molecules detected in the fingerprints were actually used by the individual, instead of deposition through simple physical handling. Such knowledge would allow law enforcement personnel to conclusively identify drug users.
Consequently, the scientists focused on detecting both drugs and drug metabolities, the molecules produced by your body when it processes drugs. If a drug metabolite is detected in fingerprints, it's a safe bet that that individual has been using drugs, and not simply handling them.
First, marijuana-using volunteers placed their fingerprints onto a glass slide. Next, the scientists coated the fingerprints with protein-coated magnetic nanoparticles designed to form a chemical bond with Δ9-tetrahydrocannabinol, the primary psychoactive component of marijuana.
After 30 minutes, the scientists removed excess nanoparticles using a magnetic brush, a tool commonly used by forensic scientists to reveal fingerprint details. Finally, the scientists chemically bound a bright dye molecule to the nanoparticles (for microscopic visualization), and rinsed away excess dye.
Success of the drug detection method.
The scientists successfully detected marijuana in the fingerprints. Importantly, details in the fingerprints were clearly visible, such as ridge patterns and sweat pores.
Such details are used by forensic scientists to identify the individual who made the prints. Thus, this technique enables confirmation of drug use while leaving characteristic fingerprint details intact.
The scientists also successfully detected other relevant moelcules with this technique. These include methadone (prescribed for heroin and morphine addicts), 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (the major metabolite of methadone), and benzoylecgonine (the major metabolite of cocaine).
Volunteers who had not used the drug in question gave a negative result after undergoing the fingerprint imaging protocol. Thus, the method is specific and accurate.
Further advantages of the protocol.
Other scientists have previously reported methods to detect drugs in fingerprints, while leaving the fingerprints intact. However, this method requires only inexpensive instrumentation (a stereomicroscope and a magnetic brush) that is already used by forensic scientists.
Additionally, the method is portable (can be used in the field), and detects low concentrations of drugs. These advantages render this drug detection protocol applicable to real-world uses.
for more information:
Hazarika, P.; Jickells, S. M.; Wolff, K.; Russell, D. A.
Imaging of latent fingerprints through the detection of
drugs and metabolites.
Angew. Chem. Int. Ed. 2008, 47, 10167-10170.