Date of Award
Master of Science (MS)
First Advisor or Mentor
Contact traces are an important part of DNA casework, but the probative value of any identified associations depends on the possibility of passive transfer. There is known individual variation in DNA left behind during contact, this DNA shedding propensity has an effect on whose DNA is detected. This study evaluated this variability using a cell staining approach. Volunteers were asked to deposit a fingerprint on a clean glass slide, then wash their hands and deposit a second fingerprint after a 30-minute wait without touching anything. Three sets of samples were collected over three consecutive weeks. Fingerprints were stained with a fluorescent cell dye (PromegaTM Diamond Dye) and signals were scored under a fluorescent microscope.
The cell staining method worked well and gave clear signals. Cell counts showed high variability across donors (n=24), as well as across the three collection events. Overall, washed hands had significantly lower cell counts than unwashed hands. The data did not show a significant difference between male and female cell counts. Reproducibility in individuals for separate collection events was low for unwashed hands and more consistent for washed hands. This is expected, since sample collection after handwashing and inactivity prevents variability due to external factors. Washed hands showed a wide range of cell counts, and high variability between individuals which reflects differences in shedding propensity, but the distribution seemed continuous. There was no correlation between cell counts and resulting DNA concentrations, which could be due to the presence of cell free DNA.
Small-Davidson, Natalee, "Reproducibility of Individual DNA Deposits detected through Cellular Fluorescence" (2021). CUNY Academic Works.