In this work, we present two new methodologies of improving the performance of microchip-based electrochemical detection in microfluidic devices, one involving the use of 3-dimensional microelectrode arrays and the other based upon platinized electrodes.  The first part describes the fabrication and characterization of epoxy-embedded gold microelectrode arrays that are evenly spaced, easily modified, and polishable.  Electrodepositions using a gold plating solution can be performed on the embedded electrodes to result in a 3-dimenional pillar array that, when used with microchip-based flow injection analysis, leads to an 8-fold increase in signal (when compared to a single electrode), with the limit of detection (LOD) for catechol being 4 nM.  By manipulating the deposition times and resulting pillar heights, pillar arrays are also used to form planar membranes between two parallel PDMS microchannels to permit small molecules to cross from one channel to another with cells being excluded by the membrane. For detecting analytically challenging molecules such as nitric oxide (NO), platinization of electrodes is commonly used to increase sensitivity.  It is shown here that microchip devices containing either the pillar arrays or more traditional glassy carbon electrodes can be modified with platinum black for NO detection.  In the case of using glassy carbon electrodes for NO detection, integration of the resulting platinized electrode with microchip-based flow analysis resulted in a 10 times signal increase relative to use of a bare glassy carbon electrode.  In addition, it is shown that these electrodes can be coated with Nafion to improve selectivity of NO over interfering species such as nitrite.  The LOD for NO when using the platinum black/Nafion-coated glassy carbon electrode was 9 nM.  The applicability of these sensitive and selective electrodes was demonstrated by monitoring the ATP-mediated release of NO from endothelial cells immobilized in a microfluidic network.

Encapsulated electrodes for microchip devices: Microarrays and platinized electrodes for signal enhancement of nitric oxide detection

246th National Meeting (2013)

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