Abstract
The development of field effect transistor (FET) based sensors for the detection of ionic species in solution is described. This development started about 35 years ago with the invention of the ion-sensitive field effect transistor (ISFET) for the detection of solution PH. Later chemically sensitive field effect transistors (CHEMFETs) have been developed for the detection of many different cations and anions. The first CHEMFETs were based on ion-selective membranes deposited physically on the gate oxide of an ISFET. More durable CHEMFETs were made by linking all membrane components covalently. Applications of field effect based sensors are discussed. The possibilities of a new generation of sensors, based on hybrid organic semiconductor field effect transistors (HOSFETs) are described.