Differential OCP Measurement

Taking advantage of its high-input impedance, low-output impedance, and miniaturization, the metal-gate FET is being used to measure variations in the open-circuit potential that occur upon interaction. Recently, direct OCP measurements using an instrumentation amplifier have been performed resulting in reliable detection of protein interactions [36]. 

The open-circuit potential was measured in real time by using an ultra-low input bias current instrumentation amplifier, providing an accurate differential measurement of voltage. The very high input impedance and very low input bias current minimize the effect of the measurement on the OCP. The gain of the amplifier was set to 1 in order to eliminate instability effects, temperature drift, etc., of the external resistor needed to set a higher amplifier gain. 

The functionalized gold electrode and the reference electrode were connected to the amplifier differential inputs (see Fig. 3.6). The amplifier output voltage, equal to the open-circuit potential for 

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The simplest on-chip circuit that can be conceived is for differential OCP measurement, although complex electrostatic discharge protection needs to be incorporated. 

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