A simple REFET for pH detection in differential mode

A simple reference field-effect transistor (REFET) for pH detection in differential mode measurements is described. The device is based on a pH-insensitive polymeric PVC membrane cast on the gate insulator of an ion-sensitive field-effect transistor (ISFET) device, that has been previously silylated. The REFET shows low pH sensitivity (1.8 mV/pH) and is only slightly affected by the concentration of Na+ and K+. The pH response of a combined solid state device consisting on a pH ISFET (of 45 mV/pH sensitivity), the REFET and a quasi-reference electrode (QRE) (Pt) is 43.7 mV/pH from pH 2 to 9. (C) 1999 Elsevier Science S.A. All rights reserved.