Session: Parallel session 7 - Club jeune SFSM

Added values of desorption electrospray ionization for mass spectrometry imaging of fingerprints processed by Oil Red O

Mass spectrometry imaging (MSI) has attracted increasing attention for forensic investigation due to its ability to profile and map chemicals at the surface of samples such as fingermarks. Amongst ionization techniques with surface sampling capabilities, desorption electrospray ionization (DESI) was successfully employed to produce high-quality images of chemicals in latent fingermarks on various substrates. Yet, latent fingermarks are most often processed with enhancement techniques to make them visible on investigated surfaces and have thus their chemical composition modified by the staining reagent. This study investigates compatibility of Oil Red O (ORO) with DESI to assess applicability of MSI into real forensic cases.

Ionization of ORO as well as its interaction with model lipid species were first investigated independently of surface extraction using electrospray ionization tandem mass spectrometry (ESI-MS/MS). Then, both enriched and natural fingerprints were subjected to DESI-MSI after ORO staining.

ESI-MS(/MS) revealed that ORO is actually a mixture of closely related compounds, with two major species respectively lacking one and two methyl groups beside the expected 408.2 Da molecule. Apart from slight suppression effects, no significant interaction was noticed between the ORO reagent and model lipid compounds during these experiments. For enriched fingermarks, DESI-MSI enabled clear visualization of fingerprint ridges and minutiae based on triolein signal in the positive mode whereas substantial delocalization of linoleic acid was observed in images recorded the negative mode. In ORO-processed natural fingerprints, low abundance endogenous triglycerides could clearly be detected. Most notably, since DESI is a soft process that maintains structure integrity, ORO impurities were valued to produce MS images of higher quality than optical ones for natural fingermarks revealed on colored porous substrates.