Innovations in latent fingerprint analysis for forensic applications with matrix assisted laser desorption/ionization mass spectrometry imaging

Abstract

This dissertation presents work that aims to address the current limitations of latent fingerprint analysis in the forensic science field and discuss innovative new ways that matrix assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) could be used to develop techniques that would alleviate some of the current issues. The first chapter consists of a general introduction to MALDI-MSI and presents a general workflow for a MALDI-MSI experiment. The sixth and final chapter summarizes the work presented in this dissertation and provides a future outlook. The second chapter discusses the compatibility of MALDI-MSI and one of the most common forensic development techniques for latent fingerprints, cyanoacrylate fuming. An array of endogenous and exogenous compounds were studied to determine if there were any changes in structure (reactions with cyanoacrylate) or signal due to the fuming process. None of the compounds exhibited any structural changes and most had comparable signal intensity with or without cyanoacrylate fuming. One class of compounds, however, quaternary ammonium derivatives (present in many hygiene products) had significantly suppressed signal after fuming. The third chapter studies the cyanoacrylate fuming mechanism in more depth based on evidence from the mass spectra in the compatibility study. Specifically, several peaks were identified that were determined to be unique to the spectra of fingerprints that had been cyanoacrylate fumed. The peaks were identified by exact mass and MS/MS and were found to be dimers and trimers of ethyl cyanoacrylate. In addition, some further studies were done to determine which endogenous compounds are responsible for the adherence of the cyanoacrylate polymer to the fingerprint ridges. It was determined that the most polymer formation happens on fatty acids and amino acids, which must play an important role in the fuming process. The fourth chapter outlines how endogenous fingerprint compounds diffuse from the fingerprint ridges over time. The initial idea was to model the diffusion of a triacylglycerol (TG) in an attempt to determine the time since deposition or age of the fingerprint. It was thought that a TG would diffuse more slowly than fatty acids (FAs), which had been researched previously by another group, and would allow for aging over a longer time period. However, it was determined that the surface interactions between fingerprint compounds and the sample substrate played a larger role in the diffusion rate than the molecular weight of the compounds. For example, the more hydrophobic TG only diffused slower than the