Urease, EnFET

A new development in the field of potentiometric enzyme sensors came in the 1980s from the work of Caras and Janata (72). They describe a penicillin-responsive device which consists of a pH-sensitive, ion-selective field effect transistor (ISFET) and an enzyme-immobilized ISFET (ENFET). Determining urea with ISFETs covered with immobilized urease is also possible (73). Current research is focused on the construction and characterization of ENFETs (27,73). Although ISFETs have several interesting features, the need to compensate for variations in the pH and buffering capacity of the sample is a serious hurdle for the rapid development of ENFETs. For detailed information on the principles and applications of ENFETs, the reader is referred to several recent reviews (27, 74) and Chapter 8. 

Furthermore, the gate area of pH-sensitive ISFET s (ion-sensitive field-effect transistor) has been covered with pH changing enzymes, such as urease and )8-lactamase [12]. Furthermore, ATPase, glucose oxidase, and trypsin were used for ATP, glucose, and peptide ENFET s (enzyme-field-effect transistor). 

The modification of the ISFET gate by immobilization of various enzymes results in a number of enzyme-FETs (EnFETs) [1 ] Generally hydrolytic enzymes eg urease or penicillinase were applied Principal problems of these sensors rise from the dependence on the buffer capacity and the pH-sensitivity of the enzyme s activity... 

A urea-sensitive ENFET is constructed by immobilizing urease on a pH ISFET. The pH at the enzymatic layer varies in the presence of urea... 

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