Simultaneous imaging of latent fingermarks and detection of analytes of forensic relevance by laser ablation direct analysis in real time imaging-mass spectrometry (LADI-MS)

Abstract

Traditional analysis of latent fingermarks using dusting powders and cyanoacrylate fuming uncovers only the physical pattern of the fingerprint ridges, neglecting vast amounts of chemical information within the residue that could divulge more about the owner. Imaging mass spectrometry provides a means to retain the fingerprint ridge detail for identification while also revealing additional chemical information. The technique laser ablation direct analysis in real time imaging-mass spectrometry (LADI-MS) was applied to image the spatial distributions of small molecules of potential forensic relevance in latent fingermarks on non-conductive surfaces. By using this approach, no solvent, matrix, or high-vacuum conditions were required. An index finger was exposed to cocaine, psychoactive “legal high” plant material, pseudoephedrine, or the explosive RDX, and a fingermark was subsequently deposited on a glass slide for analysis. LADI-MS revealed the spatial distribution of endogenous cholesterol (localized to fingerprint ridges) and simultaneously detected the psychoactive small molecules cocaine, yangonin (derived from Piper methysticum), pseudoephedrine and the explosive RDX in latent fingermarks. The spatial distribution mapping of cholesterol in a lifted print on the non-conductive adhesive side of tape was also accomplished. The ion images of endogenous compounds and detection of exogenous molecules reveal details of chemical exposures, while connecting the exposure to the owner of the print.