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Polymer modified carbon fiber-microelectrodes and waveform modifications enhance neurotransmitter metabolite detection

Raju, Dilpreet, Mendoza, Alexander, Wonnenberg, Pauline, Mohanaraj, Sanuja, Sarbanes, Mulugeta, Truong, Carly, Zestos, Alexander G.
Analytical methods 2019 v.11 no.12 pp. 1620-1630
5-hydroxyindoleacetic acid, adsorption, anions, carbon, carbon fibers, coatings, detection limit, dopamine, electrochemistry, electrostatic interactions, homovanillic acid, liquid chromatography, metabolites, microdialysis, microelectrodes, neurotransmitters, polyethyleneimine
Carbon-fiber microelectrodes (CFMEs) have been used for several years for the detection of neurotransmitters such as dopamine. Dopamine is a fundamentally important neurotransmitter and is also metabolized at a subsecond timescale. Recently, several metabolites of dopamine have been shown to be physiologically important such as 3-methoxytyramine (3-MT), 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA). Many of these neurotransmitter metabolites are currently only detected with microdialysis coupled with liquid chromatography with relatively low temporal and spatial resolution. Current electrochemical methods such as the dopamine waveform (scanning from −0.4 to 1.3 V at 400 V s⁻¹) are utilized to electrostatically repel anions such as DOPAC and promote dopamine adsorption to the surface of the electrode. Moreover, polymer coatings such as Nafion have been shown to electrostatically repel anions such as 5-hydroxyindoleacetic acid (5-HIAA). In this study, we develop novel polymer and waveform modifications for enhanced DOPAC detection. Applying the DOPAC waveform (scanning from 0 to 1.3 V at 400 V s⁻¹) enhances DOPAC detection significantly because it does not include the negative holding potential of the dopamine waveform. Moreover, positively charged cationic polymers such as polyethyleneimine (PEI) allow for the preconcentration of DOPAC to the surface of the carbon fiber through an electrostatic attraction. The limit of detection for DOPAC for PEI coated CFMEs with the DOPAC waveform applied is 58.2 ± 2 nM as opposed to 291 ± 10 nM for unmodified electrodes applying the dopamine waveform (n = 4). This work offers promise for the development of novel electrode materials and waveforms for the specific detection of several important biomolecules such as dopamine metabolite neurotransmitters.