New Technologies Promise Better Future Results

Sidebar to the article Extending the Time to Collect DNA in Sexual Assault Cases by Terry Taylor

A routine difficulty encountered in producing autosomal DNA profiles in rape cases is obtaining enough sperm cells for the analysis. Cells can be damaged or degraded due to time, or simply stuck to epithelial cells (those that line the cavities and structures of the body, such as the vagina), making it difficult to carry out a standard autosomal STR analysis.

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A session at the 2010 NIJ Annual Conference highlighted two promising technologies for enhancing the separation of sperm cells from other cells in a mixed sample. Gary Stacey, vice president of technology at Haemonetics Corporation, presented a technique called holographic optical trapping (HOT). HOT is an automated system now commercially available from Arryx, a Haemonetics subsidiary. This system allows small particles, such as sperm cells or cell fragments, to be directly manipulated using a computer-controlled hologram array. Stacey showed video and presented data offering evidence that HOT can separate sperm cells from female epithelial cells (or other contaminants) before micro-dissection to obtain DNA, enhancing the resulting STR analyses. The system is simple to use, provides visual confirmation of the process as it proceeds and allows video data tracking.

Henry K. Lin, a member of the Biosciences Division, of the Oak Ridge National Laboratory, discussed a microfabricated filter technology originally developed to separate metastatic cancer cells from the blood. Because sperm cells are substantially smaller than the female epithelial cells with which they are likely to be mixed in rape cases, this two-tier filtration process first selects out the larger cells, allowing the sperm cells to pass through and be drawn off separately. Experiments testing this application of the system have successfully separated sperm cells in mixtures where they were outnumbered 25 to 1, with a higher DNA recovery rate and cleaner STR profiles than are obtained with standard methods. The investigators intend to continue this research with epithelial cell-to-sperm cell ratios up to 100 to 1.

Ballantyne explained the importance of such research: "If we can separate sperm cells accurately and efficiently in challenging samples, it will permit standard autosomal DNA analysis in more cases. This will be a great move forward."

Date Created: March 3, 2011