Novel Carbon-Based Microelectrodes for Neurotransmitter Detection

Carbon-fiber microelectrodes (CFMEs) are used with fast scan cyclic voltammetry (FSCV) to detect neurotransmitters in vivo. 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. Though glass has been used for over twenty years, alternative insulations are sought that can be used to insulate alternative nanomaterials that cannot withstand a vertical capillary puller. Polyimide coated capillaries can be used to insulate nanomaterials, though the manufacturing process is tedious and not amenable to mass production.
Here, a new fabrication method is developed to insulate carbon-fiber and other microelectrodes with a thin epoxy coating. A CO2 laser was used to etch channels in a Teflon mold where carbon fibers were epoxy insulated in the oven. They were then silver epoxied to gold pin that connected to the head stage of the potentiostat to form an electrode. Epoxy insulated CFMEs perform comparably to glass insulated CFMEs and have been successfully used as in vivo sensors.
This thesis will examine electrodes made from alternative nanomaterials with epoxy insulation. The thorughly examined poly(vinyl alcohol) (PVA) carbon nanotube (CNT) fiber was epoxy insulated to form an electrode material and used to detect dopamine with fast scan cyclic voltammetry. Wetspun polyethyleneimine (PEI) CNT fiber microelectrodes were also constructed using epoxy insulation. PEI-CNT fiber microelectrodes displayed increased sensitivity and faster electron transfer kinetics with respect to PVA-CNT fiber microelectrodes. PEI-CNT fiber microelectrodes also exhibited a resistance to surface fouling from serotonin and 5-hydorxyindoleacetic acid (5-HIAA), a metabolite interferant of serotonin that is present in concentrations ten-times higher than serotonin.
Recently, chlorosulfonic-acid was found to be the first true solvent for carbon nanotubes. Chlorosulfonic acid wet-spun CNT fibers were also used to make electrodes using epoxy insulation. These electrodes were found to be more sensitive than other carbon nanotube fiber microelectrodes due to their larger surface areas, lack of polymer/surfactant impurities, and the lack of the use of sonication which reduces CNT length and lowers conductivity. The sensitivity towards dopamnine found to be independent of the wave application frequency, similar to PEI-CNT and CNT-Yarn fiber electrodes. This could allow us to measure neurotransmission closer to the rate at which actually occurs. Lastly, plasma enhanced chemical vapor deposition (PECVD) was used to grown carbon nanopetals (edge-plane graphene) onto metal wires. The high conductivity of the metal substrate is appealing because it would not hinder electron transfer. PECVD is used because it covers the entire wire in carbon for a complete surface coverage without the use of metal catalysts that can be difficult to deposit onto metal surfaces.