Innovations in microchip capillary electrophoresis for the direct detection of biologically important molecules

Microchip capillary electrophoresis (MCE) and related techniques have benefits over conventional separation instrumentation, including small size, high speed (seconds time scale), and low sample consumption (pL injection volumes). These features make MCE an attractive separation method, particularly for point-of-measurement applications. This thesis will demonstrate improvements made to MCE coupled to electrochemical detection (EC) in the forms of increased sensitivity through the use of microwire detection electrodes and microwire decoupling electrodes, increased selectivity from the use of multiple detection techniques such as pulsed amperometric detection as well as dual electrode detection and improvements in the materials chemistry through the use of alternate microchip materials.; In my work I systematically addressed issues associated with MCE by improving the design and construction of EC detection electrodes. I will show that increased sensitivity and decreased detection limits are possible through the incorporation of microwire working electrodes and a microwire decoupler. The incorporation of a palladium decoupler for the isolation of separation current from the detection current allows for decreased background, and in turn, lower detection limits. I will also address the low number of detectable analytes and the lack in selectivity of DC amperometry through the use of pulsed amperometric detection (PAD) and dual electrode detection, respectively.; Materials chemistry is also beginning to play a more important role in MCE because of the use of polymers as substrate materials. Poly(dimethylsiloxane) (PDMS) has become one of the most widely used materials for microchip capillary electrophoresis and microfluidics. The popularity of this material is the result of its low cost, simple fabrication, and rugged elastomeric properties. In my work I will address many issues common in PDMS microchips through a simple extraction and oxidation of the PDMS as well as exploring alternative microchip materials. The extracted oxidized PDMS (EO-PDMS) shows a dramatic increase in separation efficiencies and a decrease in peak skew from 3.2 on native PDMS to 1.2 on EO-PDMS. The introduction of thermoset polyester (TPE) as an alternative microchip material will also be presented. TPE shows promise as a merger between the ease of fabrication and cost effectiveness of PDMS and the higher separation efficiencies and increased surface stability of other polymers such as Poly(methylmethacrylate) (PMMA) and Poly(carbonate) (PC). These benefits will be shown in the form of increased separation efficiencies and decreased peak skews.