Electrochemical Characterization of the Microfabricated Electrochemical Sensor-Array System

Microfabrication technology has been used to prepare a microchip sensor-array with six sets of platinum electrodes. Chromium/platinum (10 nm/100 nm thick) were sputtered on a borosilicate wafer and patterned by wet etching method. The electrodes were designed with working electrode area of 700×400 μm in the middle and a 200 μm wide and 2600 μm long counter electrode surrounding it from three sides in a U-shape. The connection pads (1000×1500 μm) were located at the edge of a sensor-array chip. Silicon wafer was etched through to form holes with slanting side walls for immobilization cavities. The silicon and the borosilicate wafers were adhesion bonded with SU-8 epoxy resin. The cyclic voltammetry and electrochemical impedance experiments were carried out in a three-electrode electrochemical system to characterize the fabricated sensor-array chip. The results show that the current density depends on the electrode potential sweep rate ν. Also, current density depends on the concentration of potassium hexacyanoferrate(III). At slow potential sweep rates (ν≤0.01 V s−1) the steady-state signal is achieved and the electrodes behave as micro-electrodes. Such an array is a promising candidate for fast and simple biochemical oxygen demand (BOD) measurements.