Self-Assembled Monolayers of Polythiophene “Molecular Wires”: A New Electrode Technology for Neuro-Robotic Interfaces

Abstract

This thesis presents the proof of concept of a new type of electrode for inter- faces between living nervous systems and electronic devices ("neuro-robotic interfaces"). Such interfaces have long been pursued due to their high clin- ical and scientific value. However, progress has been hindered by inade- quate performance of the implanted electrodes that bridge biological, ion- based electricity and analog/digital electronics. These electrodes provoke inflammatory reactions in surrounding tissue and often cause detrimental effects when stimulating neurons to deliver information. The most promis- ing approach to improving electrode biocompatibility involves electrically polymerizing conductive polymers with biomolecules on metal electrodes. These coatings improve mechanical biocompatibility, attract neurons to the electrode, and lower electrode impedance. They are nevertheless limited by delamination of polymer from the electrode and inability to pattern or con- trol the composition of the polymer/biomolecule blend. The new electrode technology described herein addresses those limitations through two innovations: the use of self-assembled monolayer (SAM) tech- nology to bind polythiophene conductive polymers to metal electrodes, and the design of lipophilic polythiophenes ("molecular wires") that can in- sert into a cell membrane and provide stable intracellular electrical access. Thiol-based SAMs should increase coating robustness and will permit better controllability and patterning, while still offering the same biocompatibility as electropolymerized coatings. Intracellular access that does not kill the target neuron will permit gentler and more specific stimulation and higher fidelity recording. Polythiophene SAMs are thinner than electrodeposited polymer films, and thus do not decrease impedance to the same degree, but should be able to compensate for this by allowing intracellular stimulation. Data from atomic force microscopy, cell culture, and impedance spec- troscopy are combined to show that functionalized polythiophenes can form SAMs and that these SAMs have the appropriate biological and elec- trical activity for a neuro-robotic interface electrode. The feasibility of polymer-based intracellular electrophysiology is demonstrated through ar- tificial lipid bilayer experiments and atomistic molecular dynamics simu- lations of the membrane-polymer interface. Taken together, these studies constitute proof of concept for the "molecular wire" SAM electrode and represent the first steps towards development and deployment of this new interface technology.