The ability to prosecute a sexual assault case often relies on the availability of DNA evidence. It has been reported that 72% of jurors anticipate seeing DNA in a sexual assault trial  and that juries are 33 times more likely to convict when presented with DNA evidence. This presents a problem in the quest for justice because the process of manually extracting DNA from sexual assault kits can be time consuming and labor intensive. The consequence is a nationwide backlog of unprocessed kits.
“Backlogs of sexual assault cases have long been, and continue to be, a challenge throughout the U.S.,” says Dr. Susan Greenspoon.
With funding from the National Institute of Justice, Dr. Susan Greenspoon and colleagues from the Virginia Department of Forensic Science sought to increase the efficiency of processing sexual assault kit samples to help reduce the backlog. Specifically, the researchers automated a key step in the process that separates sperm cells from other cells —known as the DNAse I procedure — by using the Biomek® NXP robotic platform.
Faster Speed With Comparable Results
The Biomek® NXP platform uses robotics and software to automate the DNA extraction process. For processing mixed DNA samples from sexual assault kits, the Biomek® NXP robotic platform offers these benefits:
- Increased efficiency and speed.
- Minimized risk of contamination or degradation of samples.
- Standardization of the procedure, both within and between labs.
Greenspoon and colleagues began by creating a small-scale validation study using a limited number of samples to ensure that the automated DNAse I procedure would work. Researchers sampled cheek, vaginal, and rectal swabs of four anonymous female donors and semen from one male. They placed the seminal fluid onto the swabs that contained the female samples, then dried them prior to testing. This study confirmed that the procedure on the robotic platform was reliable and accurate.
The team then expanded to a larger-scale study with more samples. The results of both the small-and large-scale validation studies showed that the automated DNAse I procedure successfully extracted high-quality DNA that was suitable for analysis.
Compared to manual methods, researchers who used the automated procedure processed more samples in a shorter time. According to the researchers, the robotic method for differential extraction could replace the current manual method for sexual assault casework. (See "What Is Differential Extraction") When compared to the manual method, the robotic platform produced comparable:
- Yields of Y chromosomal DNA, which comes from males, and autosomal/Y chromosomal ratios. This is important because of the forensic value of Y chromosomal and autosomal DNA.
- Sensitivities for recovery of intact sperm samples which tend to provide higher quality DNA.
- Rates of reproducibility.
- Impact from contaminants.
- Frequency of cross-contamination (which was low).
Cost May be a Barrier, but Protocol is Freely Available
The automated robotic platform extraction procedure provides a new tool for crime labs to improve the speed of differential DNA extraction. However, the cost of implementing the automated procedure may be a barrier for some crime labs. Implementing a robotic platform for sexual assault sample processing requires a significant financial investment and technical expertise. The amount of time saved in the lab may offset the costs to some degree.
Using robotics within the differential DNA extraction process may also raise concerns among practitioners about DNA yields and the quality of the results. For this reason, it is crucial that the platform is programmed correctly and regularly maintained to avoid errors or malfunctions.
“This award improves the workflow for sexual assault samples and case outcomes,” notes Tracey Johnson, physical scientist at National Institute of Justice. “The researchers have made a fully functioning, automated DNAse differential extraction method and script designed for the Biomek® NXP automated platform available for dissemination to all interested laboratories.”
While automation brings new challenges and considerations, it also has the potential to vastly improve the field of forensic DNA analysis, furthering the pursuit of justice for victims of sexual assault. The success of this project highlights the importance of the continued investment in forensic science research and development and its impact on the criminal justice system.
Sidebar: What is Differential Extraction?
Differential extraction is a technique that scientists use to isolate DNA from a mixture of sperm cells and epithelial cells, which line the internal and external surfaces of the body. Sexual assault kit samples often contain a mixture of male sperm cells as well as male and female epithelial cells.
The use of automation for differential extraction relieves examiners from performing the three or more required sperm pellet washes. Given that each wash step takes approximately five minutes, automation of the extraction process could increase efficiency considerably.
About This Article
The work described in this article was supported by NIJ grant number 2019-NE-BX-0002 awarded to Virginia Department of Forensic Science.
This article is based on the grantee report “Adaptation of the DNAse I procedure to the Biomek® NXP robotic platform for more efficient and automated sexual assault sample processing” (pdf, 34 pages), by Susan Greenspoon, Ph.D., Virginia Department of Forensic Science.
[note 1] Donald E. Shelton, Young S. Kim, and Gregg Barak. “A Study of Juror Expectations and Demands Concerning Scientific Evidence: Does the ‘CSI Effect’ Exist?” Vanderbilt Journal of Entertainment and Technology Law 9 (2006): 331-368.
[note 2] Michael Briody, “The Effects of DNA Evidence on Sexual Offence Cases in Court,” Current Issues of Criminal Justice 14 (2002): 159.
[note 3] Any products and manufacturers discussed on this site are presented for informational purposes only and do not constitute product approval or endorsement by the U.S. Department of Justice.