Three-Dimensional Impedance-Based Sensors for Detection of Chemicals in Aqueous Solutions

In this work, the development of three-dimensional impedance-based biochemical sensors for detection of chemicals and biological agents in aqueous solutions is presented. The sensors are made of a stack of suspended electrodes that allow the solution to occupy the space between them and create a larger interface area between the aqueous solution and the electrodes. Increasing the solution-electrode interface area drastically changes the impedance of the sensor-solution resulting in a better sensitivity. Low concentrations of di-ethylhexyl phthalate (DEHP) in deionized water are used as the target chemical to demonstrate the advantage of new design over conventional planar interdigitated sensors. Experimental measurements are carried out to characterize the response of the planar and 3D sensors and their Nyquist plots are compared, displaying significant sensitivity improvement in 3D sensors. An electrical model for the sensors is developed that considers different physical phenomena such as doublelayer capacitance, solution resistance, Warburg effect and parasitic parameters. Nonlinear interpolations of the experimental data show that the equivalent electrical circuit is in good agreement with the Nyquist plots obtained from test data. The curve fitting of the tested data to the equivalent electrical circuit displays good agreement between the model and the tested data.