Imaging of Fingerprints Using Mass Spectrometry Enables Scientists to Distinguish Between Persons Who Touched Cocaine Versus Those Who Ingested Cocaine
by Doug Ankney
Melanie Bailey, a forensic scientist at the University of Surrey, revealed that by using a high-resolution mass spectrometry (“HRMS”) method to detect cocaine in fingerprints, she and her team can now distinguish between fingerprints left by persons who had ingested cocaine and fingerprints left by persons who had merely touched cocaine.
In 2017, Bailey reported that HRMS could detect cocaine in fingerprints—but she had not considered that one in ten non-drug users are exposed to cocaine through environmental factors. This meant that detection of cocaine in a fingerprint wasn’t conclusive evidence of cocaine ingestion.
But the new research has changed all of that. Acquiring one fingerprint sample from each of four individuals who had touched and from four who had ingested it within 24 hours, the research team imaged the samples using desorption electrospray ionization (“DESI”), matrix-assisted laser desorption (“MALDI”), and time-of-flight secondary ion mass spectrometry (“ToF-SIMS”). DESI and MALDI both demonstrated the ability to detect differences in fingerprints deposited after ingestion versus touch of cocaine. Imaging results show ingestion is characterized by a higher intensity of benzoylecgonine (“BZE”) in the area of fingerprint deposition. The ToF-SIMS imaging results eventually matched those of DESI and MALDI. But only after modification via the use of advances in ion gun technology. Employing a water cluster SIMS source, the same high BZE-to-cocaine intensity ratio over the fingerprint area was detected using ToF-SIMS.
“In forensic science, being able to understand more about the circumstances under which a fingerprint was deposited at a crime scene is important,” said Bailey. “This gives us the opportunity to reconstruct more detailed information from crime scenes in the future. The new research demonstrates that this is possible for the first time using [HRMS] techniques.”
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