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Development of a Procedure for Dielectrophoretic (DEP) Separation of Sperm and Epithelial Cells for Application to Sexual Assault Case Evidence

NCJ Number
Date Published
January 2009
50 pages
This study examined the feasibility of using a chip-based approach, dielectrophoresis (DEP) as an alternative to the differential extraction procedure currently used by most forensic DNA analysts in separating male sperm and female epithelial cells in samples from alleged cases of sexual assault.
Based on microscopic inspections, the results show that DEP can be used to separate sperm and epithelial cells into pure fractions; however, at the current stage of development, the standard chemical differential extraction procedure is faster and provides better purity and yield in the sperm cell fraction than the DEP procedures researchers have examined thus far. DEP is the movement of cells in the presence of a nonuniform electric field. Researchers assessed the use of a commercially available DEP system, the Silicon Biosystems SlideRunner-DEPSlideTM system, which is used for separating sperm and epithelial cells in a microfluidic, chip-based format. Current practice in most crime labs involves separating the sperm and epithelial cells by using a differential extraction method that relies on chemical differences in the proteins that compose the sperm and epithelial cell membranes. This extraction procedure - which consists of a sequence of labor-intensive digestion, centrifugation, and wash steps - has served the forensic community adequately for over two decades; however, this approach is not readily adaptable to higher-throughput operations (e.g., for automation on a liquid-handling robotic platform), nor is it ideally suited for the kind of reduced-scale operations required for microfluidic-based, "point-of-contact" devices that are currently under development for forensic DNA analysis. This prompted the search for new approaches for separating sperm and epithelial cells that could be more readily adapted to high-throughput and/or reduced-scale analysis methods. Extensive figures, 7 references, and appended introduction to dielectrophoresis and the Silicon Biosystems DEPSlideTM System

Date Published: January 1, 2009