FIELD-EFFECT TRANSISTORS AS TRANSDUCERS IN BIOSENSORS FOR SUBSTRATES OF DEHYDROGENASES

A specially designed field-effect transistor (FET) with a significantly enlarged gate area was applied in a classical urea enzyme FET (ENFET). The resulting high stability and sensitivity toward pH shifts make it predestinated for the measurement of H+ produced in the equilibrium of NAD(+)-dependent enzymatic reactions, especially when the equilibrium is shifted by a subsequent reaction. As a mode, the glucose dehydrogenase (GDH) reaction connected to a ion-sensitive field-effect transistor (ISFET) is demonstrated by which glucose could be determined in the range from 1 to 40 mM. A platinum electrode on the gate of the FET permits the measurement of reduction equivalents (NADH) by means of the recently reported chronopotentiometrical methods. Thus, in principle a way toward a redox-ENFET is shown.