Revealing chemical evidence from fingerprints through matrix-assisted laser desorption/ionization - mass spectrometry imaging

Hinners, Paige
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This dissertation presents my efforts to advance the application of matrix-assisted laser desorption/ionization - mass spectrometry imaging (MALDI-MSI) to the chemical analysis of latent fingerprints. The first chapter contains a general introduction to MALDI-MSI, with a focus on the application to fingerprint analysis. The final chapter summarizes the presented work and future directions for the research.

The second chapter presents the feasibility of using carbon fingerprint development powder (CFP) as an existing MALDI matrix. This study compared the ionization efficiency of CFP and other commonly used MALDI matrices. The data revealed that CFP is comparable or better than the currently utilized MALDI matrices for latent fingerprint analysis. MALDI-MSI was performed on fingerprints dusted with CFP and lifted with forensic lifting tape, demonstrating that more realistic samples can also be analyzed using MALDI-MSI. Most importantly, it was shown that MALDI-MSI does not destroy the fingerprint during analysis and the fingerprint can be preserved as forensic evidence.

The third chapter investigated the use of titanium oxide development powder (TiO2) as a MALDI matrix and elaborates on the impact of adding additional matrices to the signal-to-noise (S/N) ratio of fingerprint compounds. It was demonstrated that TiO2 worked efficiently as an existing MALDI matrix and did not require the use of a high-resolution mass spectrometer. Additional matrices on top of the TiO2 showed limited success and caused a decrease in intensity for some compounds. However, additional matrix did allow the analysis of TiO2 developed fingerprints in negative mode. Importantly this work emphasized the need for knowledge of traditional matrix applicability in fingerprint analysis.

In the fourth chapter, the potential for using MALDI-MSI to develop lifestyle profiles of unknown individuals is presented. Prior work studying exogenous fingerprint compounds focused on illicit substances. In this work, compounds related to consumer products, foods, and beverages could be detected in fingerprint residue using MALDI-MSI. These specific compounds could be used for brand or subtype determination of a particular source, such as subtype of citrus fruit. Each set of compounds detected tells a portion of an individual's lifestyle.

In the fifth chapter, the mechanism of degradation of unsaturated triacylglycerols (TGs) in fingerprints aged under ambient environment conditions was investigated. MALDI-MSI was used to explore TG profiles of fresh and aged latent fingerprints. With time, the unsaturated TGs underwent ambient ozonolysis resulting in a decrease in the abundance of unsaturated TGs that was relatively reproducible in an individual. In addition, two sets of peaks emerged with time, and were determined to be degradation peaks of unsaturated TGs due to ambient ozonolysis. The decrease of unsaturated TGs can be monitored to establish the time since deposition, or age, of latent fingerprints.

fingerprint chemical profiling, forensic science, Mass spectrometry imaging, matrix assisted laser desorption ionization