Integrated all-diamond ultramicroelectrode arrays: optimization of faradaic and capacitive currents

Integrated all-diamond ultramicroelectrode arrays (UMEAs) were fabricated using standard photolithography processes. The array consisted of typically 45 ultramicroelectrodes with a diameter of 10 μm and with a center-to-center spacing of 60 μm. The quasi-reference and counter electrodes were made from conductive diamond and were integrated on a 5 × 5 mm(2) chip. On the UMEA, a high ratio of faradaic current to capacitive current was achieved on heavily boron-doped and hydrogen-terminated diamond surfaces at slow scan rates and in high concentration of supporting electrolyte. A sensitive and reproducible detection of dopamine was achieved on hydrogen-terminated diamond UMEA at slow scan rates. The detection limit of dopamine in the presence of ascorbic acid was 1.0 nM, which is 50-100 times lower than that obtained on the macrosized boron-doped diamond electrodes. This array is promising for sensitive and reproducible detection of analytes in solutions with low detection limits.