Semiconductor-based micro-biosensors

Through two specific examples, the possibilities offered by silicon-based micro-biosensors are presented: the urea-ENFET (enzymatic field-effect transistor) and the impedimetric immunosensor. We have shown that an optimization of the urea-ENFET is possible using permselective membranes chosen regarding their charge properties and the measurement medium (increase of sensitivity, lower detection limit, larger dynamic range). Electrical properties are of primary importance for the development of immunological sensor; the use of well-defined silicon/silica heterostructures joined to a detailed impedance analysis has shown the feasibility of direct immunosensing with a detection limit of about 10 ng ml(-1) for alpha-fetoprotein. (C) 1997 Elsevier Science S.A.