UC San Diego

There is a growing interest in the use of carbon and its allotropes for microelectrodes in neural probes because of their inertness, long-term electrical and electrochemical stability, and versatility. Building on that interest, we introduce a new electrode material system consisting of an ultra-thin monolayer of graphene (Gr) mechanically supported by a relatively thicker layer of glassy carbon (GC). Gr has impressive electrical and electrochemical properties. On the other hand, GC is one of carbon’s important allotropes and consists of 3D microstructures of graphene fragments. Further, GC has exceptional chemical inertness, good electrical properties, high electrochemical stability, purely capacitive charge injection, and fast surface electrokinetics coupled with lithography patternability. This makes GC an ideal candidate for addressing Gr’s lack of out-of-plane rigidity through providing a matching sturdier and robust mechanical backing. Combining the strengths of these two allotropes of carbon, we introduce a new metamaterial Graphene- Glassy Carbon (GrGC) synthesis. We present the fabrication technology for the microelectrodes and the accompanying pattern transfer technology on flexible substrate and report on the bond between these two allotropes of carbon through FTIR, surface morphology through SEM, topography through AFM, and nanostructure study through molecular dynamics and STEM imaging. A long-term (18-weeks) in vivo study of the use of these GrGC microelectrodes assessed the quality of the ECoG-based neural signal recording and stimulation through electrophysiological measurements. The probes were demonstrated to be functionally and structurally stable over the 18-week period with minimal glial response – the longestreported so far for graphene-based microelectrodes.