Published February 15, 2022 | Version v2

Molecular imaging of humain hair with MeV-SIMS: a case study of cocaine detection and distribution in the hair of a cocaine user

  • 1. Jožef Stefan Institute
  • 2. The Maastricht MultiModal Molecular Imaging institute, Maastricht University
  • 3. Rudjer Bošković Institue
  • 4. Jožef Stefan Institute and Department of Biology, Biotechnical Faculty, University of Ljubljana
  • 5. The Maastricht MultiModal Molecular Imaging institute, Maastricht University and KU Leuven Toxicology & Pharmacology

Description

Human hair absorbs numerous biomolecules from the body during its growth. This can
act as a fingerprint to determine substance intake of an individual, which can be useful
in forensic studies. The cocaine concentration profile along the growth axis of hair
indicates the time evolution of the metabolic incorporation of cocaine usage. It could be
either assessed by chemical extraction and further analysis of hair bundels, or by direct
single hair fibre analysis with mass spectroscopy imaging (MSI). Within this work, we
analyzed the cocaine distribution in individual hair samples using MeV-SIMS. Unlike
conventional surface analysis methods, we demonstrate high yields of nonfragmented
molecular ions from the surface of biological materials, resulting in high chemical
sensitivity and non-destructive characterisation. Hair samples were prepared by
longitudinally cutting along the axis of growth, leaving half-cylindrical shape to access
the interior structure of the hair by the probing ion beam, and attached to the silicon
wafer. A focused 5.8 MeV 35 Cl6+ beam was scanned across the intact, chemically
pristine hair structure. A non-fragmented protonated [M+H]+ cocaine molecular peak
at m/z = 304 was detected and localized along the cross-section of the hair. Its
intensity exhibits strong fluctuations along the direction of the hair’s growth, with
pronounced peaks as narrow as 50 micrometres, corresponding to a metabolic
incorporation time of approx. three hours.

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