Impedance Resonance: A Novel Technique for Signal Acquisition From Interdigitated Electrodes (IDE) in Sensor Applications

A simple and useful modification to the common method of acquiring the impedance spectrum of modified interdigitated electrodes consists of including an appropriately sized induction coil connected in parallel with the interdigitated electrode (IDE). The resulting impedance behavior of the IDE/coil combination transforms the customary Bode plot of total impedance versus frequency data from a broad, complex curve to a simple resonance peak which can serve as the basis for a sensor output signal. The exact frequency and amplitude of the impedance resonance peak are a function of both the fixed induction characteristics of the coil and the experiment-dependant capacitance of the modified IDE. Quantifiable changes in the impedance resonance peak have been correlated with experimental parameters such as the electrical characteristics of polymer coatings on the IDE array leads, exposure of the IDE to aqueous solutions of varying composition, and molecular mobility factors in curable polymer resins.