Characterization and Optimization of Interdigitated Ultramicroelectrode Arrays as Electrochemical Biosensor Transducers

Interdigitated ultramicroelectrode arrays (IDUAs) were fabricated on glass wafers and investigated to obtain optimal oxidation and reduction reactions of potassium ferro/ferrihexacyanide, Fe2+/3+(CN)6, when using a 2-electrode set up. These electrodes will be used as transducers in portable microfluidic-based biosensors in the future for the detection in an aqueous, biocompatible matrix. IDUAs were designed to maximize the signal-to-noise ratio (S/N) investigating electrode height, gap size, finger width, and material. Interesting differences in the electrode materials gold and platinum were found, which were due to the oxidization of platinum and gold during the IDUA fabrication process. It resulted in gold IDUAs being by far superior in respect to signal-to-noise ratio and overall signal magnitude to those made of platinum. The effects of gap size, electrode width and number of electrode fingers were as expected. Optimal electrode heights were in the range of 70 nm–140 nm, much larger and smaller electrodes had lower signal-to-noise ratios due to overall reduced signal or increased background. The optimized IDUA was made out of gold, had 400 fingers with a finger width of 2.7 μm, a finger height between 70 nm and 140 nm and a gap size of 0.9–1 μm. A detection limit of as low as 0.1 μM ferro/ferrihexacyanide measured in a simple 2-electrode set up was obtained with a signal-to-noise ratio of 9.7.