Acoustic trapping of sperm cells from mock sexual assault samples

We report the successful separation of sperm cells from a relevant composition of mock sexual assault samples using a novel acoustic differential extraction (ADE) technology. A multi-layer microfluidic device fabricated in a non-photolithographic process from glass and polydimethylsiloxane (PDMS) was capable of interfacing with custom-built instrumentation to exploit a standing acoustic wave for the trapping of individual sperm cells in a sample containing an abundance of epithelial cells. Samples were generated from buccal and vaginal swabs to mimic post-coital vaginal swabs, and processed through the ADE system followed by DNA extraction of the captured cells with amplification of DNA using a custom short tandem repeat (STR) chemistry. The prototype acoustic trapping technology was fully capable of isolating intact sperm cells from mock samples with disparate masses of male and female DNA. Other biological components were evaluated for adverse effects on sperm cell trapping, including blood, yeast, and bacteria (E. coli), and these had negligible effects on observed sperm cell trapping. Finally, we demonstrate the successful capture of sperm cells from mock samples containing a 40-fold excess in female epithelial cells over sperm cells. The effectiveness of sperm cell purification was ascertained with polymerase chain reaction (PCR) amplification of STR loci from the male fraction post separation with an 18-plex amplification kit, which resulted in male-only profiles.