Defense Date
2023
Document Type
Directed Research Project
First Advisor
Christopher Ehrhardt
Second Advisor
Catherine Connon
Third Advisor
Kate Philpott
Abstract
Biological mixtures containing DNA from more than one contributor can make DNA profile interpretation challenging, especially for ‘touch’ or trace biological evidence. One approach to improve this is by differentiating cell populations from separate individuals prior to DNA profiling by utilizing intrinsic features of cells such as size, shape, and biochemical profiles. The goal of this study was to develop a new method for detecting and separating contributor populations in biological mixture samples using flow cytometry, a rapid and non-destructive approach with an unexplored potential for forensic casework. To accomplish this, two different mixture systems were investigated (1) mixtures containing blood and epidermal tissue and (2) mixtures containing buccal and epidermal tissue. Results showed that cells from each tissue source exhibited distinct differences in “forward scatter”, “side scatter”, and “autofluorescence profiles”. Specifically, cell populations from epidermal tissue showed lower median side scatter to autofluorescence ratios averaging compared to cell populations from buccal tissue, 1.19 and 1.31, respectively. Conversely, cell populations from epidermal tissue showed higher median autofluorescence compared to blood cell populations, which showed a median ratio of 1.10. These trends were consistent within the red/APC fluorescence channel for all tissue types. Buccal cell populations exhibited median autofluorescence intensities orders of magnitude higher than epidermal cells in most mixture samples tested. In the next phase of the project, size and autofluorescence signatures were used to develop a method to physically sort contributor cell populations using FACS. Although our DNA profiling results suggest that certain cell contributor populations were not entirely enriched after sorting, FACS still has the potential as a front-end cell separation method for forensic DNA casework.
Rights
© The Author(s)
Is Part Of
VCU Master of Science in Forensic Science Directed Research Projects
Date of Submission
5-5-2023