Carbon Nanotubes Grown on Metal Microelectrodes for Dopamine Detection

Directly growing of carbon nanotubes (CNTs) on microelectrodes using chemical vapor deposition (CVD) can provide a dense and vertically aligned CNT film. Vertically-aligned CNTs grown on carbon fibers microelectrodes can detect dopamine, but the low conductivity of the carbon fiber may lead to slow electron transfer kinetics and the intrinsic electrochemical activity of carbon fibers makes evaluating the effect of CNT enhancement difficult.  In this study, we compared vertically-aligned CNTs gown on metal wires and carbon fibers as microelectrodes. Scanning electron microscopy shows that aligned CNTs can be grown on metal wires, particularly Tantalum and Niobium wires.  Using fast-scan cyclic voltammetry, CNT-coated niobium (CNT-Nb) microelectrodes had higher sensitivity and lower DEp values compared to CNTs grown on carbon fibers or other metal wires.  The limit of detection for dopamine at CNT-Nb microelectrodes is 11±1 nM, which is approximately five times lower than CNT grown CFMEs. Using Langmuir isotherms to model adsorption/desorption processes revealed that dopamine oxidation is more reversible at CNT based microelectrodes than that for CFMEs.  CNT-Nb microelectrodes were useful for monitoring stimulated dopamine release in anesthetized rats. Other neurochemicals could also be detected, including ascorbic acid, DOPAC, serotonin, adenosine, and histamine and the enhancement for dopamine was greater than ascorbic acid at CNT-Nb electrodes.  This study demonstrates that CNT-grown metal microelectrodes, especially CNTs grown on Nb are useful for sensitive monitoring of neurotransmitters.