Development of circuit models for electrochemical impedance spectroscopy (EIS) responses of interdigitated MEMS biochemical sensors

Biochemical sensors using electrochemistry impedance spectroscopy often exploit electrical circuits to explain the electrochemical phenomena in the sensor-solution systems such as charge transport, double-layer effect and diffusion. Interdigitated sensors presented in the literature use a variety of circuits with different components and configurations to express the electrochemistry of the system. This work provides a comprehensive analysis of different electrical circuits used to interpret the system's behavior. A MEMS interdigitated sensor is used to obtain Nyquist plots of different concentrations of di-ethylhexyl phthalate (DEHP) in deionized water. The experimental data are used to examine equivalent electrical circuits with different levels of circuit complexity and for different frequency ranges. A curve fitting software is used to fit the circuit model to the tested data, and the results show equivalent circuits that include different electrical components and configurations can successfully predict the behavior of the system and explain electrochemical phenomena in the sensor-solution system. The circuit designs show that more complicated circuit models, using separate interfacial components for each electrode, may provide more accurate results, but they also may create complications in the curve -fitting optimization process. The circuit models and analysis presented here can be utilized for different biochemical sensing applications. (c) 2020 Elsevier B.V. All rights reserved.