Bio-field-effect transistors as detectors in flow-injection analysis

The development of enzyme-modified bio-field-effect transistors (BioFETs) for the determination of glucose, urea, penicillin G, penicillin V and cephalosporin C is reported. BioFETs are produced by covering the pH-sensitive gate areas of ion-selective field-effect transistors with enzyme membranes. The characteristics of the resulting BioFETs and the influence of several parameters, e.g., pH and buffer capacity, are described. The measuring range covers 1-2 orders of magnitude of substrate concentration, and the BioFETs are applicable for 3-12 weeks, depending on the enzyme. They show a short response time and are well suited for detection in flow systems. The frequency of determination with BioFETs in flow systems is high (15-20 measurements per hour). The application of a BioFET in on-line bioprocess control is described. A glucose oxidase FET monitors the glucose concentration during cultivation of Escherichia coli. The results correspond well with off-line liquid chromatographic determinations.