Fabrication of oxygen electrode arrays and their incorporation into sensors for measuring biochemical oxygen demand

Miniature Clark-type oxygen electrode arrays were fabricated using thin film technology. Each oxygen electrode comprised a silver cathode and a Ag/AgCl anode. The use of a dry electrolyte containing polyvinylpyrrolidone (PVP) permitted the use of solid state fabrication processes. The electrolyte was left dry until it was used, when the water essential for oxygen reduction was introduced through a gas-permeable membrane and absorbed by the PVP. The miniature oxygen electrode arrays showed good characteristics for monitoring dissolved oxygen concentrations and could be mass produced with assured quality. The yeast Trichosporon cutaneum was immobilized onto the cathode of an oxygen electrode using a photo-crosslinkable resin and the response of the sensor was the difference between the output of a yeast-immobilized electrode and that of a bare oxygen electrode. Measurements using the dual-type sensor for biochemical oxygen demand (BOD) were markedly simplified as air-saturated samples were not required, so air pumps and stirrers can be omitted from the sensing system. The BOD sensor was used for the analysis of real samples and the results agreed well with those determined using the conventional 5-day BOD determination method. This is a significant step toward the development of a portable BOD measuring system incorporating disposable electrodes and containing no mechanical parts.