Probing a conducting polymer by proton-coupled electron transfer of biosimilar redox molecules†

In bioelectronics, the preservation of host homeostasis upon alteration of the electrical charge caused by an implantable electrode has not yet been addressed properly. Here, we propose an in vitro strategy to evaluate the appearance of acidic regions in conducting polymer film electrodes due to the hosting of proton-coupled electron transfer (PCET) of bioinspired redox quinone molecules. The effects of electrode-inherent ion transport selectivity as well as the media-inherent buffer capacity on the response of a molecular pH probe, being the quinone redox process, were evaluated using the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). The hosting of the PCET, within the phase of the mixed ion–electron conductor, affects both the surrounding characteristics and the diffusion of the redox molecules. The involvement of di-anion quinone in the primary doping of the conducting polymer results in slowing down its diffusion within the bulk of the porous electrode. The redox process, imposed on the porous electrode in the weakly buffered media, controls the electrode operation in vivo. This leads to the appearance of two acidic regions located at the electrode bulk and at the interface between the electrode and the hosting electrolyte, respectively. The proposed methodology is highly relevant for the pre-evaluation of porous electrodes for various (bio-)technological applications.