A simple reference field-effect transistor (REFET) for pH detection in diff
erential mode measurements is described. The device is based on a pH-insens
itive 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 affec
ted 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. (
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