A PROTOTYPE BIOSENSOR BASED ON TRANSPORT PROTEINS - ELECTRICAL TRANSDUCERS APPLIED TO LACTOSE PERMEASE

We report on the development of a lactose sensor based on the transpor t protein lactose permease (LP) which cotransports lactose and H+ ions in a strictly stoichiometric ratio of 1:1. The sensor is realized by reconstituting LP in E. coli lipid vesicles which spread on hydrophili c oxide surfaces thereby forming supported phospholipid bilayers (SPBs ). Essential for the function of this biosensor is first the buffer ca pacity of the solution and second the small volume of water entrapped above the gate of an ion-sensitive field-effect transistor (ISFET) to monitor pH changes upon lactose changes. In the present study the infl uence of these two parameters on the sensor performance was investigat ed. Ellipsometry was used to estimate thicknesses and refractive indic es of the ISFET overlayer sandwich. Thicknesses were independently det ermined by a biochemical tracer technique.