Epoxy insulated carbon fiber and carbon nanotube fiber microelectrodes

Carbon-fiber microelectrodes (CFMEs) are typically constructed from glass capillaries pulled to a fine taper or from a polyimide-coated capillary that is 90 μm in outer diameter. Here, a new fabrication method is developed to insulate carbon-fiber microelectrodes with a thin epoxy coating. A polytetrafluoroethylene (Teflon) mold was laser etched with channels 30–40 μm deep and wide and each channel filled with Armstrong C7 epoxy. A carbon fiber was laid into each channel so that the fiber extended past the mold, and the epoxy cured in an oven. One end of the fiber was trimmed to about 100 μm to form a cylindrical carbon-fiber microelectrode, while the other end was attached to a pin and connected to a potentiostat. Epoxy-insulated electrodes were tested with fast-scan cyclic voltammetry. For dopamine, the sensitivity is similar to glass and polyimide-coated capillary electrodes with a linear range of 0.1–10 μM and a LOD of 24 nM. SU-8 epoxy was tested as an alternative insulator because it cures at a lower temperature using light, but it was more brittle. Carbon nanotube fibers were also successfully insulated with epoxy. Epoxy-insulated CFMEs were used to detect stimulated dopamine release in vivo. Epoxy-insulated electrodes are smaller in diameter than polyimide-coated capillary electrodes and amenable to mass production. They are advantageous for use in higher order mammals, where glass is not permitted, and with alternative electrode materials, such as carbon nanotube fibers, that cannot be fabricated in a capillary puller.