Fabrication and electrochemical properties of an interdigitated array electrode in a microfabricated wall-jet cell

A miniaturized wall-jet cell combined with an interdigitated array (IDA) el ectrode was fabricated for application as a detector for small volume flow injection analysis and capillary electrophoresis. The IDA electrode with ei ght pairs of microbands was fabricated by photolithography, sputter deposit ion and the lift-off technique on a narrow glass plate. We installed the el ectrode in a miniaturized wall-jet cell with flow channels and guides for f used silica capillaries and electrodes. The micro-channel was fabricated by using a dicing saw. The IDA electrode which had a small total area was ali gned close to a fused silica capillary (50 mum i.d.) perpendicular to the e lectrode. This made it possible to reduce the active volume of the cell to 0.44 nl. The anodic current of the redox species reached its steady state v alue in 14 s because of the small cell volume even when the solution was in jected into the flow cell at a how rate of 20 nl/min. The signal at the IDA electrode was effectively enhanced by redox cycling at a low flow rate sin ce the collection efficiency rapidly increases above 0.8 with decreasing fl ow rate despite of the small number of band electrodes in the IDA (eight pa irs). As a result, we calculated that the detection limit had a low value o f 4 nM by comparing the signal obtained at a flow rate of 1 mul/min and the baseline noise level, An enhanced dopamine peak could be obtained at the L DA electrode after electrophoretic separation in the fused silica capillary . These results clearly indicate that the IDA electrode is suitable as a de tector for small volume analysis such as microcolumn liquid chromatography and capillary electrophoresis. (C) 2000 Elsevier Science B.V. All rights re served.