Development of an impedance-based interdigitated biochemical sensor using a multiuser silicon process

An impedance-based interdigitated biochemical sensor is presented in this work that is designed and fabricated using a standard polycrystalline silicon process. The sensor provides a near real-time, non-invasive, label free and rapid detection technique to quantify chemicals and biomarkers in aqueous solutions. The combination of sensor structure and aqueous solution creates an equivalent electrical circuit comprised of constant and variable capacitive and resistive elements such as solution resistance and double-layer capacitance formed at the interface of the electrodes surface and the solution. The equivalent circuit and its elements are used to quantify the concentration of chemicals in an aqueous solution using the impedance of the system. Diethylhexyl phthalate (DEHP) solution is utilized to characterize and analyze the sensor's response via electrochemical impedance spectroscopy. Finite element analysis and experimental data are used to determine the components of the equivalent circuit. The experimental results show that the sensor is able to detect the concentration of DEHP as low as 0.02 ppm. Using the circuit model and experimental data, the change of double-layer capacitance and solution resistance of the system for different solution concentrations are obtained. The results show that the double-layer capacitance increases with solution concentration, while the solution resistance decreases. The experimental results also verify the electrical circuit model used for the sensing system.