A University lab headed by Chemistry Prof. James Landers is working with forensics labs to develop a more efficient process of separating sperm cells from epithelial cells, which would have an important impact on sexual assault cases.
DNA samples from sexual assault cases often contain a mixture of sperm cells from the perpetrator and epithelial cells from the victim. In order to identify and sequence the DNA, these cells must first be separated.
“You have a cell mixture dominated by the female,” Landers said. “You need to separate [the two types of cells]. If female DNA contaminates male DNA, defense lawyers could have a potential heyday.”
Traditionally, the swabbed sample is swished in a solution containing a small amount of detergent, causing the epithelial cells to burst while the sperm cells are protected by protein disulfide bonds and remain intact. The sperm cells are then isolated from the mixture through methods such as centrifugation, which can be time-consuming. The process can take between four and 14 hours for a single sample, Landers said, creating a significant backlog of DNA samples.
Landers is working on a procedure for isolating sperm cells that could take only 20 minutes to process one sample. After rupturing the epithelial cells with detergent, Landers uses a method known as ‘acoustics’ to trap and isolate the sperm cells. In Landers’ method, sound waves create a low pressure zone which allows smaller material to pass through but traps sperm cells. If unwanted materials the same size as sperm cells are trapped, they can be separated based on differences in density and compressibility, Landers said.
The National Institute of Justice reported a backlog of more than 100,000 DNA samples in 2010. This delay can hold up court cases and make identifying perpetrators of sexual assault very difficult, Landers said. Backlogs of this sort can create serious problems for sexual assault crimes that carry short statutes of limitations.
Landers, who has been working on this project since 2006, said he hopes to see his procedure widely used in forensics labs within two to three years.
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