Date of Award
Doctor of Philosophy (PhD)
Steven A. Soper
The research presented in this document is focused on the development and characterization of novel microfluidic devices using X-ray photolithography in poly(methyl methacrylate) (PMMA). A conductivity detector cell was developed and characterized as a sensitive detector for DNA and KCl using flow injection, then was integrated into a high-performance liquid chromatography system for the purification of PCR amplicons. A planar conductivity cell was then developed on a microchip and its detection sensitivity was characterized by pressure pumping KCl through the detector and monitoring the change in conductivity. Also, the topography of the device was characterized using scanning electron and optical microscopy images. A novel computer-controlled mechanical syringe-pump is described which uses a piezoelectric actuator and a pivoted lever for amplification of the linear displacement of the piezo to deliver solvents free from pump pulsations at volumetric flow rates approaching 1 nanoliter per minute even at high loading levels (high output pressures). The piezo-pump was found to adequately deliver stable flow of solutions with loading pressures as high as 3.79 x 10 5 Pa (actual loading pressure at the piezo = 3.41 x 106 Pa). Monitoring the flow stability using fluorescence indicated that the volume flow was fairly noise-free at pumping rates from 4--150 nL/min. A diffuser/nozzle system was fabricated which allowed automatic refilling of the syringe pump and was micromachined into PMMA using X-ray lithography. The diffuser/nozzle system contained channels that were 50 mum in depth and tapered from 300 to 30 mum. The modification of a PMMA surface was demonstrated and characterized by monitoring the contact angles of water and laser-induced fluorescence confocal microscopy. The surface was shown to be amenable to attachment of biomolecules. A Hae III restriction enzyme was immobilized on the surface of the PMMA and used for solid phase DNA digestion without affecting the activity of the enzyme. Also, 35-mer single-stranded oligonucleotides were immobilized to PMMA and hybridization experiments were performed which demonstrate the utility of the PMMA substrate for DNA microarrays applications.
Mcwhorter, Christopher Scott, "Development of Miniaturized Devices Using X -Ray Microlithography in Poly(methyl Methacrylate) for Chemical Monitoring and Microfluidic Applications." (2000). LSU Historical Dissertations and Theses. 7280.