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Sperm Capture Using Aptamer Based Technology

NCJ Number
Date Published
June 2014
42 pages
The Denver Police Department Crime Laboratory, in collaboration with SomaLoci, Inc. (Boulder, CO), identified and developed a DNA aptamer-based system for sperm-binding, isolation, and purification for DNA analysis in sexual assault cases.
This is the first aptamer-based system used in whole cell sperm captures and adapted for use with forensic casework samples. Subsequent short tandem repeat (STR) DNA analysis showed clean male DNA profiles from sperm cells eluted from cotton swabs, the preferred method for rape kit evidence collection. SOMA-based sperm cell separation is comparable to existing differential extraction-based methods; however, more rapid sample processing allows for sperm purification and DNA extraction to be completed in significantly less time. Over the last several years, a class of DNA aptamer molecules called SOMAmers (Slow Off-rate Modified Aptamers) has been identified; they bind specifically to sperm heads and tails. Several SOMAmer candidates have been further selected with the ability to bind sperm under very stringent and selective conditions. Conditions that support both efficient sperm cell elution from cotton swabs and capture using SOMAmer-coated magnetic beads were identified by screening numerous combinations of detergents, salts, and buffer additives. When tethered to magnetic beads using Biotin and Streptavidin linkers, selected SOMAmers demonstrated efficient affinity-based purification of sperm cells from eluates of mock forensic samples that contained a mixture of HeLa cells and sperm cells or female buccal cells and sperm cells. Further research is ongoing in optimizing these SOMAmers under various stringent and forensically relevant conditions, so as to develop an inexpensive and rapid system for sperm cell capture adapted for automation, using robotic workstations commonly found in forensic laboratories. A full forensic validation will be conducted to address reproducibility, sensitivity, and reliability with both mock and adjudicated forensic case samples. 8 figures, 1 table, and 20 references

Date Published: June 1, 2014