Directed Research Project
Sarah J Seashols-Williams, Ph.D.
Tracey Dawson Green, Ph.D.
Joseph Reiner, Ph.D.
Cell mixtures are often seen in forensic samples and commonly involve sexual assault cases where mixtures of sperm cells and vaginal epithelial cells are frequently encountered. This produces challenges in downstream analysis in the form of STR mixture profiles. The only method currently in use in crime laboratories for front-end sperm and epithelial cell separation is differential extraction. This method often results in STR mixture profiles due to carryover into both the male and female fractions and suffers from a wide range of efficiency depending on the laboratory or individual processing the sample. Optical trapping offers an alternative method for cell mixture separation by allowing cells to be individually selected and physically removed from a mixture. Previous studies exploring this method utilized an open droplet technique which had issues in the transferal of cells in a clean manner and displayed a high contamination potential. This research aimed to combine a microfluidic device with the optical trapping method to combat these issues. A microfluidic device was developed which allowed mixture samples to be passed through a micro-channel while target cells could be manipulated away and physically separated into a separate chamber downstream. Using this method, spermatozoa were trapped to produce a total of 13 single-source semen samples and 11 separated sperm cell:epithelial cell mixture samples. Separated cells were removed from the device and processed downstream using a standard forensic workflow. Resulting STR profiles demonstrated that this method produced minimal drop-in and female donor contributions from the trapped sperm fractions while producing full profiles from as few as 31 cells, with consistent full profiles observed with as few as 41 cells. Overall, this novel optical trapping microfluidic device allows for sperm cells to be successfully separated from a liquid mock sexual assault sample in approximately one hour and produces samples that can be immediately processed through a forensic workflow.
© The Author(s)
Is Part Of
VCU Master of Science in Forensic Science Directed Research Projects
Date of Submission