| Abstract
| - This work describes the fabrication and evaluation of apoly(dimethyl)siloxane (PDMS)-based device that enablesthe discrete injection of a sample plug from a continuous-flow stream into a microchannel for subsequent analysisby electrophoresis. Devices were fabricated by aligningvalving and flow channel layers followed by plasma sealingthe combined layers onto a glass plate that containedfittings for the introduction of liquid sample and nitrogengas. The design incorporates a reduced-volume pneumaticvalve that actuates (on the order of hundreds of milliseconds) to allow analyte from a continuously flowingsampling channel to be injected into a separation channelfor electrophoresis. The injector design was optimized toinclude a pushback channel to flush away stagnant sampleassociated with the injector dead volume. The effect of thevalve actuation time, the pushback voltage, and thesampling stream flow rate on the performance of thedevice was characterized. Using the optimized design andan injection frequency of 0.64 Hz showed that the injection process is reproducible (RSD of 1.77%, n = 15).Concentration change experiments using fluorescein asthe analyte showed that the device could achieve a lag timeas small as 14 s. Finally, to demonstrate the potential usesof this device, the microchip was coupled to a microdialysis probe to monitor a concentration change andsample a fluorescein dye mixture.
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