ABSTRACT
A biosensor can be obtained by a combination of field effect transistor (FET) and biological material, with conductance changed by the biological reaction. Among the ion-sensitive FET (ISFET)-based biosensors, research on ISFET with an immobilized enzyme membrane has been the most developed, with the ion concentration change accompanying the enzymatic reaction detected by the ISFET. An immuno-FET detects a charge excess at the FET surface due to an immunochemical reaction. In the ISFET, instead of the gate electrode used in the metal oxide semiconductor FET, an ion-sensitive membrane is formed on the channel region. When sensor chips are extracted from a wafer by cutting, there is no need to insulate the cut edges. In ISFET-based enzyme sensors, a differential measurement method has mostly been used because the method can compensate very effectively for temperature dependence, pH change in analyte solution, light sensitivity, and drift of the ISFET itself.
