Filtration based DNA preparation for sexual assault cases.

Police departments in the United States currently have as many as 500,000 unprocessed swabs taken from rape victims. The standard method for purifying sperm from these swabs is to resuspend first all cells and to digest selectively the excess of the victim's epithelial cells. The intact sperm are then separated from the contaminating solubilized DNA by centrifugation, careful removal of supernatant, and extensive washing of the sperm pellet, all steps that are difficult to automate. Vacuum driven filtration is an alternative method for separating sperm from digested epithelial cells that requires only pipetting steps and can be readily automated in a 96 well format. Sperm DNA is enriched 45-fold using this process and the yield of PCR ready DNA is roughly 20% of the amount originally present on the swab.