Sensing oxygen at the millisecond time-scale using an ultra-microelectrode array (UMEA)

Abstract

We report a novel sensing protocol based on ultra-short (<5ms) measurements, which is using a dedicated sensor consisting of an ultra-microelectrode array (UMEA) for monitoring the concentration in dissolved oxygen concentrations in solution. The UMEA sensor is fabricated from Pt and oxide-nitride-oxide (ONO) as an insulating material, and electrodes are recessed in a glass substrate. The UMEA sensor is operated in its linear regime, and the oxygen concentration in solution is derived in less than 5ms from the slope of the measured current I as a function of 1/√t, t being the measurement time. To validate the proposed measurement protocol and to calibrate the sensor, variations in the concentration of dissolved oxygen are monitored simultaneously using the UMEA-based sensor and an external electrochemical sensor in a 10-mL wet-cell. An excellent agreement (R2=0.994) is found between the two sensors, and a sensitivity of 0.49nAs−0.5/mg/L is determined for the UMEA sensor operated in this ultra-short measurement regime. Finally, and most importantly, the amount of oxygen consumed during the electrochemical measurements in this configuration is drastically reduced, i.e., by about 10 orders of magnitude, compared to a commercial electrochemical sensor, which is very valuable to monitor in situ the respiratory activity of microtissues in nL volumes as found in microfluidic systems.