Characterization of silylated ISFETs by ion-step measuring method

The ion-step measuring method is used to characterize Ta205 ion-sensitive freld-effect
transistors (ISFETs) which are treated with y-aminopropyltriethoxysilane (APS) to create amine groups on the surface. Different procedures of silylation are used and the stability with respect to hydrolysis is examined. It is shown to be difficult to fabricate reproducible APS layers which are stable with respect to hydrolysis. The sensitivity of the silylated ISFETs to heparin is also examined. In this case positively charged APS is used as an affinity ligand for the negatively charged heparin. The results show a linear relationship between the change in ion-step response and the heparin concentration in PBS. The silylation procedure is also used to 'tune' the ion-step response of the Ta205 ISFET in such a way that the silylated ISFET does not show a response to an ion step at pH 7. In this way the ion-step response of a porous membrane mounted on top of the gate area of the ISFET can now be specifically determined without an interfering ion-step response of the underlying ISFET.