Acoustic differential extraction for forensic analysis of sexual assault evidence.

Forensic DNA analysis of samples obtained from sexual assault evidence relies on separation of male and female components of the recovered genetic material. The conventional separation method used by crime laboratories, differential extraction (DE), is one of the most time-consuming sample preparation steps, requires extensive sample handling, is difficult to automate, and often results in inefficient separation of female DNA from the male sample components. To circumvent conventional DE, acoustic differential extraction (ADE) analysis was developed on a microfluidic device. The ADE method relies on acoustic trapping of sperm cells in the presence of epithelial cell lysate (which is unretained), and laminar flow valving to direct the male and female fractions to separate outlets. Following the separation of sperm from epithelial cell lysate, DNA extraction, quantitation, amplification, and separation were performed using conventional laboratory methods. The results show that highly purified male and female fractions can be obtained with the ADE microdevice from mock sexual assault samples in 14 min. ADE analysis provides the potential to significantly alter the means by which sexual assault evidence is processed in crime laboratories.