The measurement principle of the O2-FET is based on pH-ISFET (Ion sensitive field effect transistor) which is surrounded by a nobel metal electrode. Here a change in the oxygen content is detected via a proportional change in the pH - value. Additional it is possible to monitor - like with the Clark sensor - the current density caused by the Redox - reaction.

Here a picture of an O2-FETs is shown. To define the operating point IDS and UD are controlled constant (Sourcefollower). UNME and the Ag/AgCl reference electrode form an electrochemical cell. Changes of the pH - value cause a potential shift at the gate, which is readjusted by UD. Measurands are the voltage UGS and the current INME. If a voltage of -700mV is applied to the noble metal electrode dissolved oxygen is measured. If no voltage is applied the pH - value gets measured.

Further informations:

Wiest, J., Brischwein, M., Grothe, H., Otto, A.M., Wolf, B.: Planar Microsensors for measurement of cellular respiration. SENSOR 2005 Proceedings II 2005; II:249-54..