Microfluidic Applications in Forensic Science

The separation and detection of cells, biomolecules, and other compounds of interest are essential throughout the biochemical and forensic sciences. These separations are employed in human identification, clinical diagnostics, explosive detection, and narcotic identification, among other applications. The conventional methods and instrumentation for these purposes are labor-intensive, time-consuming, non-integrated, and have not evolved in a significant manner for decades. Microfluidic platforms can alleviate these limitations, providing rapid, cost-efficient, and automated methods for bioanalytical and forensic separations. This dissertation presents microfluidic approaches for two specific applications: sperm cell capture from sexual assault evidence, and explosive compound identification from environmental samples.
The work presented in Chapter 2 details the design, optimization, and evaluation of a microfluidic platform for acoustic trapping. This approach leverages acoustic forces to capture and purify sperm cells from sexual assault samples, eliminating non-sperm particles and free DNA in order to conclusively identifier a perpetrator. Buccal swabs, vaginal swabs, and post-coital samples were analyzed with this approach, which showed the ability to capture sperm cells effectively from samples with an excess of female epithelial cells. Chapter 3 describes the validation of this prototype instrument and microchip, during testing performed at two government forensic laboratories in Palm Beach County, Florida, and Mesa, Arizona. The acoustic trapping approach was demonstrated for authentic sexual assault samples, and compared to conventional separation methods. Following prototype evaluation at forensic laboratories, the effect of fluidic properties on acoustic trapping was investigated at a fundamental level, as presented in Chapter 4. Sample-to-sample variations in viscosity, density, and compressibility were shown to manifest in changing acoustic conditions, which can be detected through real-time electronic measurements. That real-time feedback can be used to adapt to the variable liquid properties of each sample, maintaining optimal acoustic trapping under all conditions. Finally, Chapter 5 describes an electrokinetic separation of explosive compounds, performed on a native polymeric substrate. This work shows that an underivatized polymer microchip can be used to identify multiple explosives in a rapid separation, implementing portable components that may be amenable for field use.