Polymer Modified Carbon Fiber Microelectrodes for Precision Neurotransmitter Metabolite Measurements

Abstract

Carbon fiber-microelectrodes (CFMEs) are considered to be one of the standard electrodes for neurotransmitter detection such as dopamine (DA). DA is physiologically important for many pharmacological and behavioral states, but is readily metabolized on a fast, subsecond timescale. Recently, DA metabolites such as 3-methoxytyramine (3-MT) and 3,4-dihydroxyphenylacetaldehyde (DOPAL) were found to be involved in physiological functions, such as movement control and progressive neuro degeneration. However, there is no current assay to detect and differentiate them from DA. In this study, we demonstrate the co-detection of similarly structured neurochemicals such as DA, 3-MT, and DOPAL. We accomplished this through electrodepositing CFMEs with polyethyleneimine (PEI) and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) polymers. This endowed the bare unmodified CFMEs with surface charge, physical, and chemical differences, which resulted in the improved sensitivity and selectivity of neurotransmitter detection. The differentiation and detection of 3-MT, DOPAL, and DA will potentially help further understand the important physiological roles that these dopaminergic metabolites play in vivo .

Echem methods and electrode types of the current in vivo electrochemical sensing

“…Carbon fiber microelectrodes (CFMEs) have good biocompatibility, easy insertion, and electrode diameters as small as 10 μm, making in vivo electrochemical detection more reliable. 128 …”

Review—Recent Advances in FSCV Detection of Neurochemicals via Waveform and Carbon Microelectrode Modification

“… 61 However, the two-fold selectivity came at a cost where temporal resolution suffered by 400 ms. 58 Polyethyleneimine (PEI) coatings were also applied to enhance the detection of anionic neurotransmitters such as DOPAC, 62 while PEDOT:PEI coatings helped detect and differentiate other dopaminergic metabolites such as DOPAL and 3-methoxytyramine (3-MT). 19 , 63 The sensitivity of these different analytes can be characterized by calculating the limit of detection (LOD) measurements. Having a lower LOD indicates the analyte can be detected even when present at nanomolar concentrations.…”

“…Using unmodified CFMEs with the triangle waveform, DOAPL’s oxidation peak was observed at 0.7 V. 17 When DA and DOPAL were measured together, only a single peak was observed. 63 To differentiate DOPAL’s peak from dopamine, the electrode surface was modified by the electrodeposition of the polymers polyethyleneimine (PEI) and Poly(3,4-ethyle-nedioxythiophene) polystyrene sulfonate (PEDOT:PSS). 17 The PEI coated CMFEs had higher sensitivity for DOPAL detection due to the electrodeposited polymer forming a thin, positively charged layer on the electrode’s surface, which attracted the negatively charged DOPAL.…”

“… 17 The PEI coated CMFEs had higher sensitivity for DOPAL detection due to the electrodeposited polymer forming a thin, positively charged layer on the electrode’s surface, which attracted the negatively charged DOPAL. 62 , 63 Although this enhanced DOPAL detection by repelling the DA molecules, it was not sufficient in detecting two separate peaks for co-detection.…”

Multiplexing neurochemical detection with carbon fiber multielectrode arrays using fast-scan cyclic voltammetry

“…To counter some of these drawbacks and enhance functionality as biosensors, metal electrodes have also been electrodeposited with conductive carbon-based polymer coatings to increase biocompatibility and longevity of recording capabilities [14]. Polymers, such as PEDOT, carbon nanotubes (CNTs) [15], and Nafion [16], an anionic, cation exchange polymer, have been electrodeposited onto metal surfaces for increased selectivity [17][18][19]. More recently, metal microelectrodes modified with CNTs [20] and carbon nanospikes [21] have also been used as neurotransmitter sensors with FSCV in addition to using gold-based multielectrodes arrays [22].…”