In this dissertation, several microfabricated devices are introduced to develop new applications in the area of chemical analysis. Electrochemical micropumps, chip-based liquid chromatography systems and multilayer capillary electrophoresis microdevices with crossover channels were fabricated using various substrates such as poly(dimethylsiloxane) (PDMS), glass, and poly(methyl methacrylate) (PMMA). I have demonstrated pressure-driven pumping of liquids in microfabricated channels using electrochemical actuation. PDMS-based micropumps were integrated easily with channel-containing PMMA substrates. Flow rates on the order of ~10 µL/min were achieved using low voltages (10 V). The potential of electrolysis-based pumping in microchannels was further evaluated for pressure driven microchip liquid chromatography (LC). Two micropumps were connected with reservoirs for sample and mobile phase, situated at the ends of microchannels for sample injection and separation, respectively. Columns micromachined in glass were coated covalently with an organic stationary phase to provide a separation medium. A pressure-balanced sample injection method was developed and allowed the injection of picoliter sample volumes into the separation channel. Fast (<40 s) separation of three fluorescently tagged amino acids was performed in a 2.5-cm-long microchip column with an efficiency of 3300 theoretical plates. Improved electrode designs that eliminate the stochastic formation of bubbles on the electrode surface will enhance pumping reproducibility. Multilayer polymeric microdevices having fluidically and electrically independent crossover channels were made using phase-changing sacrificial layers (PCSLs). High-performance electrophoretic separations of fluorescently labeled amino acids were carried out in multilayer PMMA microchips. Neither pressure nor voltage applied in a crossover channel resulted in negative effects on the separation quality in the main fluidic path. A fifty-fold reduction in crossover volumes was achieved in next-generation multilayered microchips. The ability to make minimal dead volume crossover channels facilitated the design and operation of multichannel array microdevices with a minimum number of electrical and fluidic inputs. Replicate electrophoretic separation of two peptides was performed in parallel for three independent microchannels connected to a single sample reservoir. My work demonstrates the value of PCSLs in making complex microfluidic structures that should expand the application of micro-total analysis systems.



College and Department

Physical and Mathematical Sciences; Chemistry and Biochemistry



Date Submitted


Document Type





Lab-on-a-chip, microfluidics, capillary electrophoresis, liquid chromatography, microdevices