Date of Award

1-1-2022

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Chemistry

Content Description

1 online resource (xvi, 187 pages) : illustrations (some color)

Dissertation/Thesis Chair

Rabi A Musah

Committee Members

Mehmet Yigit, Paul Toscano, A John Dane

Keywords

Fingerprints, Biometric identification, Chemistry, Forensic, Mass spectrometry, Ion mobility spectroscopy

Subject Categories

Analytical Chemistry

Abstract

Fingerprint evidence has long been a pillar of forensic science and has been used for over a century as a means of identifying an individual. This is accomplished through the comparison of friction ridge patterns, which are inherently unique to each individual, and the practice of visualizing fingerprints and comparing them has become a well-studied field. While these techniques have been optimized and improved over time, they generally rely only on the physical pattern to provide information about the donor, and not the content of the fingerprint material itself. In the modern era, steps have been made to extract from the fingerprint more information about the donor. This is generally accomplished through analysis of the chemical content of the fingerprint itself. Fingerprints are comprised of various endogenous, semi-endogenous, and exogenous compounds, ranging from the fatty acids and other lipids that appear in sweat, to detergents and polymers derived from the various personal care products we use, to compounds indicative of our contact with external objects and substances. These can, in turn, be categorized and processed to glean information about the donor. For example, the content and ratios of endogenous compounds in the fingerprint may be used to expose the biological sex or approximate age of the donor, while detection of markers from products like insect repellant, prescription medications, or illicit substances provide lifestyle information about the donor. In these ways, a fingerprint can be useful for more than just its physical pattern.In order to access this underutilized chemical information, mass spectrometry can be leveraged to assess the chemical composition of a fingerprint. Direct analysis in real-time high- resolution mass spectrometry (DART-HRMS) is a quick, facile technique that can be used to analyze samples rapidly, often with little to no sample preparation, and therefore can be used as a high throughput triage approach to determine chemical composition. Following screening by DART-HRMS, matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI- MSI) can be utilized to analyze the whole fingerprint, revealing a 2D map of the distributions of the ions that are detected within it. When ions are localized to the ridges of the fingerprint, this spatial distribution ion image appears as the friction ridge pattern typically collected through more conventional development of latent fingerprints. In this way, MALDI-MSI can be used not only to reveal diagnostic ions indicative of exposure to pertinent substances, but it can also be used to establish a direct link between the donor and the substance. This analysis technique can also be used in conjunction with the statistical model random forest to reveal exposure to substances even in the absence of readily distinguishable diagnostic ions. In this work, the ability of these mass spectrometry techniques to assess an individual’s exposure to a variety of substances is demonstrated. Through the use of DART-HRMS screening, exposure to “legal high” psychoactive plant materials, illicit drugs, and explosives was detected. Utilizing MALDI-MS imaging provided not only confirmation of exposure, but also provided the friction ridge pattern of the donor, thereby linking the chemical evidence to the individual. The use of the statistical model Random Forest was demonstrated to be an effective method for unmasking exposure to compounds which did not produce identifiable diagnostic ions via MALDI-MS analysis. It was also able to reveal which of the ions, that were detected within samples, were derived from the substance of interest. The compatibility of the developed MS methods with traditional fingerprinting techniques was also assessed and was found to be unimpeded by the use of fingerprint powders, cyanoacrylate fuming, and lifting tape. The use of these techniques in tandem can be a powerful tool for connecting individuals to substances that have relevance to many fields, including forensics, homeland security, and medical diagnostics.

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