Determination of blood pO2 using a micromachined Clark-type oxygen electrode

Variation of the performance of a micromachined Clark-type oxygen electrode in decreasing the size of the cathode was examined aiming for the measurement of pO2 in whole blood. In the oxygen electrode, a cathode and an anode were formed as thin-film patterns on a glass substrate and a micro container for the internal electrolyte solution was formed on a silicon substrate by anisotropic etching. A silicone rubber gas-permeable membrane was formed on the sensitive area. Seven types of oxygen electrodes with cathodes whose dimensions ranged from 25 μm×25 μm to 500 μm×500 μm were fabricated. Linear calibration curves were obtained for the respective electrodes with correlation coefficients higher than 0.995. Flow dependence of the output current was suppressed from 10–11% with the 500 μm square cathode to 1–4% with the 25 μm square cathode. Furthermore, the flow dependence was reduced by approximately one order of magnitude with the existence of the gas-permeable membrane. Response time was also dependent on the size of the cathode and became shorter as the cathode became larger. The performance of the oxygen electrode was directly compared to a commercially available blood gas analyzer in the measurement of pO2 in whole blood. Overall, the values by the oxygen electrodes microfabricated in this study were found to be within 26% of those by the blood gas analyzer. In addition, the values by the electrodes with smaller cathodes were found to be within 8% of those by the blood gas analyzer suggesting that the microfabricated oxygen electrode can actually be used in blood gas analysis if the cathode is properly designed.