"Applying Microfabrication Technology to Forensic DNA Analysis: Cell Sorting for Isolation of Sperm from Sexual Assault Evidence "
Katie Horsman
1999 Beckman Scholar - Hope College
Presently in Ph.D. Program at University of Virginia
Forensic DNA analysis of sexual assault evidence requires differential extraction of the DNA from sperm and vaginal epithelial cells (to produce separate male and female fractions of DNA), PCR amplification, and separation of the PCR products. The ultimate goal of the current research focuses on reducing DNA analysis time in forensic laboratories by exploiting bioanalytical microdevices for each of these processing steps. This presentation will focus on the development of a microchip to replace differential extraction, the current laboratory method used for sperm and epithelial cell separations, thereby reducing the processing time without compromising extraction efficiency, purity of product, or sensitivity of the sample preparation.
The microchip separation of sperm and vaginal epithelial cells exploits the distinct physical properties of the two cell types including buoyant density, size, shape, and proclivity for adsorption to the microchannel surface. Using an etched microchannel positioned between two reservoirs and a pump-driven flow (~ 1 ?L/min), a mixture of sperm and epithelial cells can be sorted with the sperm cells directed to and collected in the outlet reservoir while the epithelial cells are retained in the inlet reservoir. Preliminary experiments employing digital video microscopy to visualize the cell separation allowed for evaluation of cell purity and efficiency of the process. Using mock post-rape vaginal swabs, the cell separation product obtained on the microdevice resulted in uncontaminated sperm cell fraction. The DNA from isolated cells was extracted with a commercial extraction kit, amplified with a COfiler® PCR kit, and analyzed on a commercial capillary electrophoresis instrument, yielding the profile of the male sperm donor. DNA extraction from the isolated cells was also performed on a microdevice before amplification and analysis to demonstrate the potential of integrating these two steps into a single device to circumvent conventional differential extraction. Refinement of such cell sorting systems, and the employment of microdevices for ‘sample in-answer out’ DNA analysis stands to impact the forensic community by dramatically reducing the time for analysis of evidence through automation of sample preparation.
Katie’s interest in forensic chemistry was cultivated by an internship at the Battle Creek Police Department Forensic Science Unit (Battle Creek, MI) during high school. Katie pursued her interest by obtaining her B.S. in chemistry from Hope College (Holland, MI) in 2000. While at Hope, she worked with Dr. William Polik on physical chemistry research entitled, “Dispersed Fluorescence Spectroscopy of Formyl Fluoride.” Katie was awarded the Beckman Scholar Award by the Arnold and Mabel Beckman Foundation in 1998 in support of this research. The work has been published in the Journal of Physical Chemistry A as well as the Journal of Molecular Spectroscopy.
Katie went on to earn an M.S. in Forensic Science from the University of Illinois at Chicago in 2001 where she received a UIC University Fellowship. While at UIC, she interned at the Illinois State Police Forensic Science Center - the forensic lab serving Chicago. She worked in the Trace Evidence Section developing a searchable IR-ATR database for use with paint comparisons. Her M.S. research was completed at the Oak Ridge National Laboratory under the direction of Dr. Michelle Buchanan. In the Organic and Biological Mass Spectrometry group at ORNL, Katie completed research in the chemical composition of fingerprints for gender discrimination and drug screening. This work was published in the Journal of Forensic Sciences.