Polyethylenimine Carbon Nanotube Fiber Electrodes for Enhanced Detection of Neurotransmitters

Abstract

Carbon nanotube (CNT)-based microelectrodes have been investigated as alternatives to carbon-fiber microelectrodes for the detection of neurotransmitters because they are sensitive, exhibit fast electron transfer kinetics, and are more resistant to surface fouling. Wet spinning CNTs into fibers using a coagulating polymer produces a thin, uniform fiber that can be fabricated into an electrode. CNT fibers formed in poly(vinyl alcohol) (PVA) have been used as microelectrodes to detect dopamine, serotonin, and hydrogen peroxide. In this study, we characterize microelectrodes with CNT fibers made in polyethylenimine (PEI), which have much higher conductivity than PVA-CNT fibers. PEI-CNT fibers have lower overpotentials and higher sensitivities than PVA-CNT fiber microelectrodes, with a limit of detection of 5 nM for dopamine. The currents for dopamine were adsorption controlled at PEI-CNT fiber microelectrodes, independent of scan repetition frequency, and stable for over 10 h. PEI-CNT fiber microelectrodes were resistant to surface fouling by serotonin and the metabolite interferant 5-hydroxyindoleacetic acid (5-HIAA). No change in sensitivity was observed for detection of serotonin after 30 flow injection experiments or after 2 h in 5-HIAA for PEI-CNT electrodes. The antifouling properties were maintained in brain slices when serotonin was exogenously applied multiple times or after bathing the slice in 5-HIAA. Thus, PEI-CNT fiber electrodes could be useful for the in vivo monitoring of neurochemicals.

Recent trends in carbon nanomaterial-based electrochemical sensors for biomolecules: A review

“…Our group has used polyethylenimine (PEI)-CNT fiber electrodes for enhanced detection of neurotransmitters. [68] Wet spinning CNTs into fibers was performed using PEI as a coagulating polymer. Compared with poly(vinyl alcohol) (PVA) CNT fiber-electrodes[69], the PEI-CNT fiber electrodes had lower overpotentials and better detection limits for dopamine, likely because they were more conductive.…”

“…[68] Figure 3 shows that the current did not decrease for repeated injections of 1 µM serotonin at PEI-CNT fiber microelectrodes, in contrast to carbon-fiber microelectrodes, which had a 50% decrease after 25 injections. The resistance to serotonin fouling at CNT based electrodes is often attributed to the higher density of edge plane sites, but the addition of oxygen groups, while maintaining a high sp 2 conjugation, may also help reduce fouling.…”

Development of Electrochemical Microsensors for in vivo Neurotransmitter Detection

“…89 In particular, fabricating CNT fibers directly into electrodes in a manner similar to CFMEs dramatically simplifies the electrode fabrication process and improves the reproducibility. 90 The first electrochemical application of a CNT fiber sensor was reported in 2003 91 and CNT fiber microelectrodes have been developed for dopamine detection using DPV 92 , chronoamperometry 89 , and FSCV. 93,94 Two distinct routes have been developed for manufacturing CNT fibers: wet-spinning a suspension of CNTs into a bath or direct spinning a fiber from a CNT forest.…”

“…Our group has successfully applied PEI/CNT fiber microelectrodes for in vivo monitoring of dopamine and serotonin in brain slice. 90 Thin, uniform fibers were fabricated by wet spinning CNTs into fibers using PEI as a coagulating polymer. In comparison to PVA/CNT fibers, PEI/CNT fibers have better LODs of dopamine (4.7 ± 0.2 nM) and lower overpotential.…”

“…106 And the best LOD for microelectrodes is 4.7 ± 0.2 nM, achieved by PEI/CNT fiber microelectrodes. 90 While most of the current experiments have concentrated on dopamine detection, future studies could expand the analytes detected and strive for better sensitivity and selectivity at smaller electrodes for a range of neurochemicals.…”