where E is the standard electrode potential, R the gas constant, T the absolute temperature, F the0faraday constant, a the activity of species i, and Z the number of moles of electron involved.iiPotentiometric sensors are divided into the metal-oxide sensitive field effect transistor (MOSFET),the light-addressable potentiometric sensor (LAPS), the ion-sensitive field effect transistors (ISFET)and the ion-selective electrodes (ISE). Ali et al. developed a commercial MOSFET using a GOxmodified ZnO nanowire. GOx-functionalized ZnO nanowires were grown on the Ag wire and thendirectly connected to the MOSFET gate (Figure 1) [54]. They tested the response time and the stabilityof the MOSFET sensor by using three different GOx/ZnO modified Ag electrodes, i.e., verticallyaligned, uniform nonaligned, and nonuniform nonaligned ZnO nanowires. The results showed that wellaligned ZnO-modified electrode displayed a good stability, short response time (<100 ms), and Sensors 2010, 104858improved detection limit. They also further demonstrated that the GOx/ZnO modified MOSFET is ableto be used for the immobilization of other biomolecules to make versatile electrodes for biosensing.Figure 1. Schematic illustration of the configuration of the MOSFET-based potentiometricglucose detection using an extended-gate functionalized-ZnO nanowire as a workingelectrode and the Ag/AgCl reference electrode (reproduced with permission from [54].Copyright 2009, IEEE)
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