Carbon nanotube (CNT) yarn and fiber-microelectrodes were developed for neurotransmitter detection using fast scan cyclic voltammetry (FSCV). Fibers were made by suspending CNTs in acid/surfactant and extruding into acetone/polyethyleneimine (PEI) and compared to a CNT yarn. They were FSCV frequency independent for dopamine up to 100 Hz. With faster frequencies, up to 500 Hz, high currents are maintained, which allows a 2 ms sampling rate for FSCV, compared to 100 ms. CNT fibers have rough surfaces which trap dopamine and dopamine-o-quinone (DOQ), creating more reversible CVs. CNT yarns and fibers are beneficial for high sensitivity, rapid measurements of neurotransmitters.