Defense Date
2023
Document Type
Directed Research Project
First Advisor
Dr. Susan Greenspoon
Second Advisor
Dr. Christopher Ehrhardt
Third Advisor
Dr. William Eggleston
Abstract
Due to advancements in DNA analysis technology and an increased ability to detect trace quantities of low template DNA, ‘touch’ or trace DNA has become a prevalent form of evidence for forensic investigations. Trace DNA is biological material left on a surface from skin cells after being touched or handled. The success rate of casework could be improved with new methods to non-destructively screen trace DNA to predict DNA yield and whether multiple cell populations are present in the evidence prior to STR analysis. Current methods of trace DNA analysis require quantifying the sample with qPCR followed by STR analysis, however, low amounts of template DNA may cause allelic drop-out or results in uninterpretable profiles both of which can reduce or even eliminate the probative value of the evidence. Androgens, such as testosterone, make a feasible biological marker for pre-DNA analysis trace samples due to varied secretion levels between individuals and possible persistence in the epidermis. Another potential target is cytokeratin molecules which are a diverse and abundant class of proteins found throughout epidermal cells.
This study surveyed variation in the abundance of either testosterone or cytokeratin antibodies in shed epidermal cells collected through direct swabs of individuals’ hands. Fluorescently tagged antibodies of either cytokeratin or testosterone were hybridized to the epidermal cells and then analyzed using flow cytometry followed by DNA analysis. The results demonstrated that although cytokeratin AE3 binding efficacy varied between individual donors, no systematic relationship was observed between probe binding and DNA yield or the presence of multiple contributor cell populations. Testosterone-stained contact samples also exhibited differences between some pairs of contributor cell populations, but there was not a clear quantitative relationship between probe binding and the presence of multiple contributors in the sample. However, testosterone abundance did show some evidence of a correlation to DNA yield (R2 = 0.66) and a stronger correlation when high yield (>1 ng) DNA samples were excluded (R2 = 0.90). Analysis of unstained contact cells showed the presence of nucleated epithelial cells in touch samples indicating a possible source of DNA in trace evidence. These results may provide a novel method for front-end analysis of trace samples pre-DNA characterization using testosterone to estimate DNA content. Additionally, the variability in antibody binding efficacy may be due to the heterozygosity within touch samples as cellular composition varied between individuals and further investigation could be to exploit these differences for distinguishing between multiple contributors. The ability to non-destructively triage and characterize trace DNA evidence prior to DNA profiling would help address the challenges associated with touch evidence to conserve valuable time and resources.
Rights
© The Author(s)
Is Part Of
VCU Master of Science in Forensic Science Directed Research Projects
Date of Submission
5-4-2023