Conducting polymers and bioinspired materials for organic bioelectronics

Organic electrochemical transistors (OECTs) have rapidly surged as amplifying transducers forbiosensing or diagnostic devices and for cells/nerves stimulation. 1 OECTs translate ionic signalsinto electric current using an electrolyte in direct contact with a conducting polymer channel.Unlike in organic field effect transistors where charge transport involves only a small layer, ionsin OECTs permeate the entire volume of the active material. This results in devices having highersignal amplification and lower operating voltage. 1 At the heart of OECTs working principle is theorganic mixed ionic-electronic conductor, usually a π- conjugated polymer (or polymer blend)able to host (or chemically linked to) charged groups.The greatest challenge of developing high-performing mixed conductors is optimizing theseemingly conflicting processes of electronic and ionic charge transport. 2 The chemical featuresof mixed conductors make them hydrophilic; however, little is known about how water and ionsaffect their microstructure and charge transport, as well as their long-term operational stabilityand biocompatibility.A successful strategy towards suitable materials for OECTs is to modify conducting polymerssuch as polythiophenes to make them hydrophilic, using glycolated substituents. 3 I am currentlyinvestigating the role of glycolated side chains in ion coordination and polymer morphology, 4,5and developing a methodology to describe swelling and morphology changes upon ionpenetration and doping in these materials.A different path towards new bioelectronic materials is to instead use natural mixed conductingpolymers that are intrinsically biocompatible, either alone or in composites. Synthetic polymersderiving from eumelanin (the black pigment in our skin, hair and eyes) are promisingbiocompatible, non-cytotoxic components in OECTs or other optoelectronic devices: 6-8 theyfeature both electronic and protonic charge carriers, can be prepared in large batches undercontrolled conditions, and easily incorporated into hybrid materials.I am currently studying the structure, self-assembly and electronic properties of eumelanin-derived materials. My model takes into account the chemical disorder of eumelanin(tautomerisation, oxidation and proton exchange sites) and aims to elucidate its effect on theelectronic structure and charge transport characteristics of this material. In particular, I aminvestigating the peculiar dipole-dependent properties of DHICA melanin 9 and itssupramolecular organisation; this rigid polymer can be spun into fibers with promisingmechanical and charge transport properties.

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