Diamond ultra‐microelectrode arrays for achieving maximum Faradaic current with minimum capacitive charging

All‐diamond ultra‐microelectrode arrays (UMEAs) were fabricated using standard photolithography processes. The array consists of typically 45 ultra‐microelectrodes with a diameter of 10 µm and with a center‐to‐center spacing of 60 µm. The quasi‐reference and counter electrodes are made from conductive diamond and integrated on a 5 × 5 mm2 chip. The arrays with different surface terminations were characterized using cyclic voltammetry and the redox couple of Fe(CN)_ 6^ 3- / 3- 4- . - 4- as probes. A peak‐shaped voltammogram was detected on electrochemically hydrogen‐terminated surface if scanned with a slow scan rate (e.g. 20 mV/s), resulting in a higher ratio of the Faradaic current (signal) to capacitive charging current (background current). A sensitive and reproducible detection of hydrogen peroxide was achieved by using the UMEA. The net‐charge for the oxidation of hydrogen peroxide at 0.4 V (vs. C) is linear with the concentration of hydrogen peroxide in the range of 6.5–650 µM. The detection limit is 2.0 µM, which is 100 times better than that obtained on the macro‐sized boron‐doped diamond electrode.