Defense Date
2023
Document Type
Directed Research Project
First Advisor
Christopher Ehrhardt
Second Advisor
Catherine Connon
Third Advisor
William Eggleston
Abstract
As more sensitive DNA profiling techniques have been developed, questions about how and when the DNA was deposited have become a driving issue in forensic casework. Image flow cytometry (IFC) offers a way to estimate the time since deposition (TSD) of trace DNA samples based on individual cells' morphological and autofluorescence properties. Previous work has shown that a TSD can be determined from a single contributor in touch samples. To determine if TSD could be correctly estimated for mixtures containing a fresh deposit (less than a week old) and an older deposit, this project characterized a series of samples that included material with a single TSD, mixtures samples containing deposits with different TSDs, and split TSDs; dividing substrates in half with two different TSDs on one side and a single TSD on the other. For each sample type, IFC was used to characterize the morphology and autofluorescence of individual cells by comparing measurements (area, contrast, intensity, and brightness detail) to be classified into the TSD. Results showed that samples with a single TSD were classified as the correct TSD time frame groups of 8 to 83 days or over 121 days. For mixtures, cells with TSD of less than 5 days could be distinguished from older deposits (8 days or older) when a minimum of 94 cells were detected in the sample. However, samples with split TSD had poor distinction and classification amongst the time groups. To determine possible causes for these TSD classifications in all samples, the morphology and autofluorescence feature values were compared to a reference database, and the cell measurements of samples with accurate classification. The reference database used is a collection of single epidermal TSD samples from one day to 415 days. Several samples were found to have brightness detail intensity greater than seen in the reference database and other samples. These fluorescence differences could be driven by TSD or by external environmental factors or an individual cell population. Overall, this research showed that biological deposits of less than 5 days could be detected even when deposits of 8 days or older are present in the sample. This could be used to identify when fresh contact cells were deposited.
Rights
© The Author(s)
Is Part Of
VCU Master of Science in Forensic Science Directed Research Projects
Date of Submission
5-16-2023