MP10: Signal Enhancement and Improved Temporal Resolution in Microchip Electrophoresis and Electrochemical Detection

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Laura A. Filla, Laura C. Mecker, Douglas C. Kirkpatrick, and R. Scott Martin

Department of Chemistry, Saint Louis University

Microdialysis sampling is an in vivo sampling technique that has been used to continuously monitor neurotransmitter release in the brain. Our group has described a valving-based microchip that integrates microdialysis sampling with microchip electrophoresis and electrochemical detection to separate and detect any sampled neurotransmitters. While this approach offers fast analysis times, detection limits and temporal resolution must be further improved to study biological systems. Initially, the use of an electrode array was investigated to improve the limits of detection; it was found that two optimally-spaced palladium electrodes offer a 2.7X improvement in signal over a single electrode of the same total area. A new method to fabricate an eight electrode carbon-ink microarray was developed with the spacing between the electrodes being such that fresh analyte can diffuse across the surface of each of the eight electrodes. Although the use of more electrodes increases the length of the detection zone and thus decreases resolution, the array has been optimized so that the best compromise between signal and resolution is achieved, with the limit of detection for norepinephrine improving from 2.8 µM to 170 nM. This poster will also address the issue of minimizing Taylor dispersion and thus conserving temporal resolution in the microchip by segmenting the aqueous microdialysate with oil droplets, which confines the sample and prevents analyte diffusion within the flowstream. A corona treatment system is used to generate a hydrophobic/hydrophilic interface downstream, which desegments the droplets into a continuous aqueous flowstream prior to analysis. This approach enables the coupling of segmented flow with microdialysis sampling, microchip electrophoresis, and electrochemical detection to provide optimal temporal resolution throughout the device. The implications of segmented flow include the ability to monitor rapid concentration changes of neurotransmitters in near real-time, which is crucial in monitoring concentration dynamics for in vivo studies.

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