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 10mm and with a center-to-center spacing of 60mm. The quasi-reference and counter electrodes are made from conductive diamond and integrated on a 5 x 5mm(2) chip. The arrays with different surface terminations were characterized using cyclic voltammetry and the redox couple of FE(CN)(3-;6) (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 0.4V (vs. C) is linear with the concentration of hydrogen peroxide in the range of 6.5-650mM. The detection limit is 2.0µM, which is 100 times better than that obtained on the macro-sized boron-doped diamond electrode.