Accurate continuous monitoring using ISFET-based biosensors based on characterization and modeling of drift and low frequency noise

The merit of a recently reported method for correction of drift in pH-sensitive ISFET's [1] is further examined by considering the distinction between drift and low-frequency noise. A physical model for drift in pH-sensitive ISFET's has been employed to isolate the low frequency noise associated with these devices. Characterization of the low-frequency noise behavior of ISFET-based biosensors, is particularly relevant to the applicability of the proposed method which is based on monitoring the differential of the sensor output signal over sufficiently small intervals of time. The validity of the reported corrective scheme for continuous monitoring of pH is experimentally confirmed under conditions approximating acute metabolic acidocis using a Si3N4-gate pH-sensitive ISFET whose noise spectrum was characterized apriori. The theoretical and experimental results presented in this work have a direct bearing on ISFET-based biosensors which detect a local pH change using a pH-sensitive ISFET, such as ISFET glucose sensors.