Chemical images on fingerprints revealed with mass spectrometry

Commercially available UV-adsorbent TiO2 nanoparticles were used to assist laser/desorption ionization in the course of matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI). Titanium nano-powders proved extremely stable and efficient for small molecule ionization, with negligible background noise in the low mass region (m/z < 500 Da). Validation steps were carried out, assessing detection limits and comparing the results to those of the established DESI/Orbitrap technique. The new analytical method was used to reveal the molecular distribution of endogenous (lipids) and exogenous (analgesics and antipyretics) compounds in latent finger marks (LFMs). The detection limits of endogenous fatty acids and small molecules such as caffeine were in the range of fmol/mm2 on LFMs. The technique separated overlapping latent finger marks, exploiting the differences in lipid expression of human skin. Finally, the method was used to prove contact between skin and objects contaminated by different substances, such as credit cards and paper clips, with chemical images that maintain the shape of the objects on the LFM.