Microfluidic Devices for Forensic DNA Analysis

Abstract

The development of integrated, miniaturized, and portable DNA analysis systems is crucial to alleviate massive backlog of unanalyzed samples and to address ever increasing demand for these assays. This thesis work contributes towards the development of a fully integrated microdevice capable of “sample in – answer out” for forensic DNA analysis. Specifically, this work describes the development of rapid and robust fabrication protocol for solvent-actuated bonding of polymeric thermoplastic substrates at room temperature, the development of microchannel wall coating strategies to eliminate analyte-wall interactions for high resolution separation of single-stranded DNA, and the characterization of a thin-film planar microwave transmission line for microfluidic heating applications. The solvent-actuated bonding protocol was based on the difference in capillary forces between the microchannel and the interstitial space between the surfaces of the two substrates to be bonded. This force differential wicked the bonding solvent into the gap between the substrates causing them to bond. The technique was implemented by placing the two substrates under moderate pressure, applying a moderate pneumatic vacuum to the fluidic channel, and introducing tens of microliter of bonding solvent through one end of the fluidic channel. The effect of bonding solvent on the dimensions of the microchannel was analyzed, and the mechanical robustness of the bonded devices was also characterized. Electrophoretic separation of single-stranded DNA (ssDNA) was successfully performed to demonstrate the functionality of these devices. To enhance ssDNA separation performance, schemes to modify poly(methyl methacrylate) (PMMA) – the primary substrate used in this work – were explored. This two step process consisted of altering surface hydrophilicity via surface activation using either nitric acid or UV/ozone followed by coating the surfaces with adsorptive polymers. Contact-angle measurements of the pristine and modified PMMA substrates were performed to quantify the change in wettability of the surface. Twofold increase in the separation efficiency was achieved by implementing these surface passivation strategies. Finally, the use of a thin-film planar microwave transmission line as a microwave power source was investigated for on-chip microwave heating of fluids. The microwave characterization data was used to develop a first-order analytic model of the microwave power absorption. The model was used to understand microwave power flow through the device and to calculate the fraction of the incident power absorbed in the fluid. Additionally, a fit of the predicted temperature obtained using this model to the measured temperature was performed to evaluate efficiency of this heating method.