Integrated ion sensors: how much more should be done?

The endeavors of a number of academic labs to address the difficulties associated with ion-sensitive field effect transistors (ISFETs) are examined. The focus is entirely on these devices, since most others, such as enzyme FETs, extended gate, and diode devices, are all based on the same principles. The focus is on several of the more troublesome areas associated with ISFETs coated with ion-sensitive membranes that have been identified and at least partially addressed. These include the problem of membrane adhesion, which is one of the problems identified relatively early on in ISFET development. The inherent interfacial stability of these devices is of obvious concern, and this point requires more attention. Problems associated with isolation and packing of the devices are reviewed.<>