INVESTIGATION OF FREQUENCY-INDEPENDENT IMPEDANCE BEHAVIOR IN CONDUCTING POLYMERS

Abstract

Biocompatibility and low, frequency-independent impedance are critical in the design of electrodes for bioelectric signal sensing applications. These conditions could be regarded as the minimum requirements in order to ensure the device performance and recorded signal fidelity. While conducting polymers have shown promise for development of sensing and stimulating bio-electrodes, their reactive impedance characteristics which result from slow ionic diffusion and double layer capacitance present challenges for designing reliable devices. Their reactive impedance, introduces a non-linear and ill-behaved high-pass filter that corrupts the recorded signal.

We have fabricated and optimized electrodes modified with a series of poly (heterolenes) that appear to exhibit low impedance which is characterized by non-diffusion-governed behavior in the frequency range relevant for physiological signals. Based on the impedance results obtained for the electrodes we have developed a model for charge transport in the polymer film which does not rely on the incorporation of the well-known Warburg element. A correlation of experimental impedance data with the proposed equivalent circuit and morphological models is also established. The concluding remarks briefly highlight the practical implications of these results and their preliminary in vivo results.