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

Abstract

A miniaturized wall-jet cell combined with an interdigitated array (IDA) electrode was fabricated for application as a detector for small volume flow injection analysis and capillary electrophoresis. The IDA electrode with eight pairs of microbands was fabricated by photolithography, sputter deposition and the lift-off technique on a narrow glass plate. We installed the electrode in a miniaturized wall-jet cell with flow channels and guides for fused silica capillaries and electrodes. The micro-channel was fabricated by using a dicing saw. The IDA electrode which had a small total area was aligned close to a fused silica capillary (50 μm i.d.) perpendicular to the electrode. 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 value in 14 s because of the small cell volume even when the solution was injected into the flow cell at a flow rate of 20 nl/min. The signal at the IDA electrode was effectively enhanced by redox cycling at a low flow rate since the collection efficiency rapidly increases above 0.8 with decreasing flow rate despite of the small number of band electrodes in the IDA (eight pairs). As a result, we calculated that the detection limit had a low value of 4 nM by comparing the signal obtained at a flow rate of 1 μl/min and the baseline noise level. An enhanced dopamine peak could be obtained at the IDA electrode after electrophoretic separation in the fused silica capillary. These results clearly indicate that the IDA electrode is suitable as a detector for small volume analysis such as microcolumn liquid chromatography and capillary electrophoresis.