APPLICATION OF ENZYME FIELD-EFFECT TRANSISTOR SENSOR ARRAYS AS DETECTORS IN A FLOW-INJECTION SYSTEM FOR SIMULTANEOUS MONITORING OF MEDIUM COMPONENTS .1. PREPARATION AND CALIBRATION

Enzymes were (co)immobilized on the pH-sensitive gates of an eight-channel field-effect transistor (FET). Glucose was analysed with a glucose dehydrogenase (GDH) FET, maltose with a coimmobilized maltase (MAL)/GDH FET, sucrose with a coimmobilized invertase (INV)/GDH FET, lactose with a beta-galactosidase (beta-GAL)/galactose dehydrogenase (GALDH)-fusion protein FET and ethanol with a coimmobilized alcohol dehydrogenase (ADH)/aldehyde dehydrogenase (ALDH) FET. These EnFETs were integrated in FIA systems, calibrated and characterized with respect to buffer capacity, pH value, stirrer speed and NAD concentration and cross sensitivity. On account of the pH and buffer capacity sensitivity of the signals of the EnFETs, the pH value was monitored with a pH-FET of the array and the buffer capacity and substrate concentration were calculated from the shape of the signal of the FIA system. The EnFETs were stored at 4 degrees C for many months without activity loss. They have satisfactory activity for performing a large number of analyses.