On the fabrication of a synthetic voltage-gated ion channel based on organic mixed ion-electron conductors

This work is intended to have the non-linear behaviour of voltage-gated ion channel artificially reproduced through the fabrication of an ionic transistor-like device, the channel of which being composed of nanoporous membrane to be filled with selected organic mixed ion-electron conductors (OMIECs) via specific electropolymerization procedures. That precise configuration, coupled with an electrochemical 4-point probe measurement and holes-injecting systems, is aimed to give full control and quantitative insights on ionic transport in conducting polymers. Therefore, device-related shape, function, physical parameters such as conductivity and permeability, behaviour under potential and concentration gradients are explored and analysed in details, in order to have them compared with well known material features and responses in a consistent way. On top of that, huge efforts are put on samples preparation and characterization, the latter being repeatedly performed for different pore-sizes and polymer, and accounting for electrochemical impedance spectroscopy analyses before and after the pores being filled, non contact and conductive Atomic Force Microscopy measurements, Scanning Electron Microscopy observations. The possibility to perform electron-gated transport of selected ions inside nanopores allows for channel ionic resistance modulation to happen. Results obtained for chloride-doped Poly(3,4-ethilendioxythiophene) show an increase in conductivity for positive gate voltages directly applied on the film; the hygroscopic nature of polyelectrolyte blends such as PEDOT:PSS make ion resistance modulation practically impossible instead. Considerations on the physics behind PEDOT:Cl behaviour lead to new insights on OMIECs properties in matter of ionic flow: mobility is demonstrated to be dependent on the applied gate voltage and selectively gated ionic motion can be easily achieved through electrically-driven holes inward and outward fluxes