Micromachined sensing module for pO2, pCO2, and pH and its design optimization for practical use

The performance of a sensing module for pO2, pCO2, and pH was tested from a practical point of view and its design was modified for the pO2 electrode and the pH combination electrode. Owing to the elongated lifetime of the on-chip liquid-junction reference electrode, pH measurement could be conducted repeatedly. The outputs from these electrodes taken in a 4.6 μl flow channel on the chip and in a 100 ml beaker were compared. Although a substantial difference was observed between the measured currents of the pO2 electrode with a 0.2 mm×1.2 mm cathode, the difference was reduced markedly by using a 25 μm×25 μm cathode. A good coincidence was observed between the values of potential obtained with the pH electrode, while the data with the pCO2 electrode suggested that it needed a substantial modification of design depending upon its applications. The sensing module was actually used to measure blood gas levels in whole human blood and the values were compared with those obtained by a commercial blood gas analyzer. The deviation of pH values was within 0.06 pH units and pO2 values were within an acceptable level. However, substantial deviations of pCO2 values were observed.