(Invited) Carbon Nanotube-Based Microelectrodes for Enhanced Neurochemical Detection

Abstract

Carbon-fiber microelectrodes (CFMEs) have been traditionally used with fast scan cyclic voltammetry (FSCV) to detect neurochemicals in vivo. However, there are several challenges in detecting neurochemical changes using bare CFMEs. First and foremost, fouling has been shown to significantly decrease sensitivity through the formation of biopolymers from serotonin and other analytes that block sites for analyte absorption. The loose sheets of graphene that make up the carbon fiber also have relatively low conductivities, which result in slow electron transfer for electrode materials and low temporal resolution. Carbon Nanotubes (CNTs) have shown to be promising for use as electrode materials. Carbon nanotubes (CNTs) are highly sp2 hybridized, which is very advantageous for measuring fast neurochemical changes in vivo. The CNTs also contain a high percentage of edge-plane carbon that is the catalytic site for neurotransmitter oxidation, which is fouling resistant. Furthermore, the cylindrical structure of CNTs provide a high aspect ratio, which allows for more sites for analyte adsorption and high sensitivity to detect low basal levels of neurochemicals. Several methods have been developed to incorporate CNTs onto CFMEs such as dipcoating; however, the method is highly variable and produces noise. Wetspinning CNTs with polymers or acids to form CNT fiber has been shown to be highly efficacious in developing novel electrode materials. For example, poly(ethyleneimine) CNT fiber microelectrodes were fouling resistant to both serotonin and 5-hydroxyindoleacetic acid (5-HIAA). They were also able to detect exogenously applied serotonin onto brain slices. Acid spun CNT fiber microelectrodes were formed with either sulfuric acid or chlorosulfonic acid that preclude the use of sonication, polymers, or surfactants, which act as impurities that reduce sensitivity.