Figure 5.

Electrochemical pH Sensors. (a) Traditional, glass electrode-based pH sensing; (b) ISFET-based pH sensing, where the gate of a field effect transistor (FET) is removed and is replaced by the interaction of solution and pH-sensitive layer to modulate the current between the drain and source of the transistor; and (c) extended gate FET (EGFET), which separates the electronic half of the ISFET from the electrochemically sensitive half in order to extend sensor lifetime and reduce drift.