Fabrication of C-MEMS Derived 3-Dimensional Glassy Carbon Microelectrodes for Neural Sensing and Stimulation

In this work, we present for the first time, the fabrication of 3 - dimensional glassy carbon microelectrodes (aspect ratio 5) for neural activity monitoring and stimulation. Prior work in this field has shown the success of 2-dimensional glassy carbon electrodes for neural activity monitoring. Firstly, precursor structures have been fabricated from direct laser writing of SU-8 layer on silicon wafer. Then as in Carbon electromechanical process (C-MEMS) steps, these structures have been pyrolyzed in an inert atmosphere of nitrogen yielding glassy carbon structures. The small size of these electrodes (diameter 55 μm and height 180-200 μm), fulfils the requirement to minimize neural tissue damage during electrode insertion. The fabrication process allows space for even smaller microelectrodes with high aspect ratio. The structures are ohmic in nature and have conductivity suitable for neural probing. The high Young's modulus (25.27GPa) and hardness (2.92GPa) help the microelectrodes to pierce the neural tissue. This is substantiated by rat studies where these microelectrodes successfully pierce into rat skin. The electrodes were also tested for their immunogenicity where no cytotoxic effects of the material were observed both invitro and invivo in mice. These studies are path breaking in field of glassy carbon microelectrodes in neural sensing applications and current work on further mechanical, electrical and biological tests based characterization of the microelectrodes is going on.