Comparison of Nafion- and overoxidized polypyrrole-carbon nanotube electrodes for neurotransmitter detection

Permselective polymer coatings improve selectivity and sensitivity of microelectrodes for cationic neurotransmitters. Immobilizing carbon nanotubes (CNTs) into these polymers should further improve sensitivity by increasing the electroactive surface area. The goal of this study was to compare the electrochemical properties of overoxidized polypyrrole (oPPY)-CNT and Nafion-CNT coated microelectrodes. Fast-scan cyclic voltammetry was used to test their response to neurochemicals. For dopamine, the average increase in oxidation current compared to bare electrodes was 3.7 +/- 0.5 for oPPY-CNT electrodes (limit of detection (LOD) 3.3 +/- 0.6 nM) and 3.3 +/- 0.8 for Nafion-CNT electrodes (LOD 4 +/- 1 nM). The selectivity for dopamine over ascorbic acid was better with oPPY-CNT electrodes. oPPY-CNT electrodes also displayed increased electron transfer kinetics for anions while Nafion-CNT electrodes did not, which proves that polymer deposition can affect the electrocatalytic properties of the CNTs. Both oPPY-CNT and Nafion-CNT electrodes were used to detect stimulated dopamine release in the caudate-putamen of anesthetized rats after 2, 4 and 12 pulse stimulation trains. oPPY-CNT electrodes could also detect small amounts of dopamine after 4 and 12 pulse stimulations in the basolateral amygdala (BLA). Although Nafion-CNT electrodes were easier to make, oPPY-CNT electrodes were more advantageous for dopamine detection because they were reproducibly fabricated, measured higher currents in vivo, and maintained selectivity over anions. The addition of CNTs to polymer coatings facilitates measurements of small concentrations of neurotransmitters in vivo.