Membrane attachment, ISFET

Ever since an ISFET that was chemically modified by a valinomycin-containing PVC membrane was reported [141], there has been general consensus on the advantages of this type of microsensor over conventional ISEs. Some serious problems have also been acknowledged, though e.g. the low mechanical stability of the membranes, the interference of COj in the potentiometric response, the lack of a stable micro-reference electrode and the relatively high drift rate of ISFETs). Attachment of the membrane can... 

FETs that can transduce other than simple protonation/deprotonation reactions have been reported in the literature. In 1975 Moss et al (20) described an ISFET that has a PVC membrane physically attached to the gate oxide of an SiOj FET in which valinomycin was introduced to obtain a K+ sensitive device. Although a response to variations in K+ concentrations was observed there are some serious drawbacks that until now have prevented that such devices can compete with or even replace conventional Ion Sensitive Electrodes. Firstly, the physical... 

If we want to apply these materials on ISFETs in addition the membrane materials should allow covalent attachment to polyHEMA, receptor molecules, and anionic sites. 

By substituting and Uqs = Ur into Eqs. (9) and (10), the dependencies of the drain current, on the activity of the ions are obtained. An analogous expression holds for CHEMFETs with another ion-selective membrane, ENFETs (enzyme-layer FETs), IMFETs (immuno-FETs), BIOFETs (with attached bioreactor containing bacteria, whole cells, tissue slices etc.) and REFETs (ISFETs with a constant activity of ions used as a reference to indicating ISFETs). 

Langmuir-Blodgett layers have a structure similar to that of natural cell membranes. They thus play an important role in biosensors. Enzymes and antibodies can be attached in this way to ISFET gates or to surface acoustic wave (SAW) sensors. 

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