Differential Light Addressable Potentiometric Sensor with Poly(vinyl chloride) and HfO₂ Membranes for pH Sensors

In this paper, a differential measurement setup for the light addressable potentiometric sensor (LAPS) is proposed. The LAPS with a HfO₂ layer as the sensing membrane was used, and different weight percentages of DNP=/(PVC + DNP) [DNP: dinonylphtalate, PVC: poly(vinyl chloride)] membrane were cast on the surface of HfO₂-LAPS. The pH sensitivity can be decreased from 58.6 to 24.5 mV/pH by using 60 wt% PVC cocktail. Then, the pH sensitivity measured through a differential circuit was 30.1 mV/pH, showing high potential for replacing the function of a conventional reference electrode as an ion-sensitive field-effect transistor (ISFET)/reference field-effect transistor (REFET) pair. In addition, to confirm the output signal of the two substrate electrodes, a specific measurement setup was used.