Carbon-fiber microelectrodes (CFMEs) have been used for several years for the detection of neurotransmitters such as dopamine.

Carbon fiber-microelectrodes (CFMEs) have been the standard for neurotransmitter detection for over forty years. However, in recent years, there have been many advances of utilizing alternative nanomaterials for neurotransmitter detection with fast scan cyclic voltammetry (FSCV). Recently, carbon nanotube (CNT) yarns have been developed as the working electrode materials for neurotransmitter sensing capabilities with fast scan cyclic voltammetry. Carbon nanotubes are ideal for neurotransmitter detection because they have higher aspect ratios enabling monoamine adsorption and lower limits of detection, faster electron transfer kinetics, and a resistance to surface fouling. Several methods to modify CFMEs with CNTs have resulted in increases in sensitivity, but have also increased noise and led to irreproducible results. In this study, we utilize commercially available CNT-yarns to make microelectrodes as enhanced neurotransmitter sensors for neurotransmitters such as serotonin. CNT-yarn microelectrodes have significantly higher sensitivities (peak oxidative currents of the cyclic voltammograms) than CFMEs and faster electron transfer kinetics as measured by peak separation (ΔEP) values. Moreover, both serotonin and dopamine are adsorption controlled to the surface of the electrode as measured by scan rate and concentration experiments. CNT yarn microelectrodes also resisted surface fouling of serotonin onto the surface of the electrode over thirty minutes and had a wave application frequency independent response to sensitivity at the surface of the electrode.

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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 .

Carbon-fiber microelectrodes (CFMEs) are considered to be the standard electrodes for neurotransmitter detection. Fast-scan cyclic voltammetry (FSCV), an electroanalytical method, has the ability to follow neurochemical dynamics in real time using CFMEs. Improvements in neurochemical detection with CFMEs were previously made through the coating of polymers onto the surface of the carbon-fiber. Polymers such as PEI, PEDOT, and Nafion were electrodeposited onto the surface of the electrodes to enhance neurochemical detection. This work demonstrates applications for enhancements in co-detection of similarly structured neurochemicals such as dopamine, DOPAL, 3-methoxytyramine, DOPAC, and other neurotransmitters. Manipulating the charge and surface structure of the carbon electrode allows for the improvement of sensitivity and selectivity of neurotransmitter detection. The analytes are detected and differentiated by the shape and the peak positions of their respective cyclic voltammograms.

Dopamine is a crucial neurotransmitter important for several behavioral, pharmacological, and disease states. Cocaine, amphetamine, and other psychostimulants elicit their effects by increasing dopamine in the extracellular space, while Parkinson’s disease is caused by the lack of extracellular dopamine due to the death of dopaminergic neurons. Techniques such as fast scan cyclic voltammetry (FSCV) have been utilized to measure extracellular dopamine and other neurotransmitters through the application of a triangle waveform, which can oxidize and, subsequently, reduce neurotransmitters at the surface of the electrode, producing a cyclic voltammogram where peak oxidative current is proportional to concentration. Utilizing FSCV with carbon fiber microelectrodes (CFMEs) is useful because the carbon electrodes are biocompatible and have both high temporal and spatial resolution. This makes the electrode amenable for the detection of neurotransmitters on a fast subsecond timescale comparable to the fast, phasic firing of dopaminergic neurons. Preliminary studies have illustrated the utility of CFMEs with FSCV for neurochemical detection in zebrafish (Danio rerio). CFMEs were implanted into zebrafish brain preserved in oxygenated buffer ex vivo with a micromanipulator. The electrodes were also inserted into zebrafish retina for the measurement of neurotransmitter release. The release of neurotransmitters was stimulated by the application of potassium chloride (KCl), amphetamine and cocaine, or electrical stimulation. Significant differences in dopamine levels were observed between wildtype control animals and hyperglycemic (diabetic) zebrafish. Moreover, behavioral assays such locomotor measurement displayed cognitive defects in hyperglycemic animals in addition to the thinning of the retina, which correlated to significant increases in extracellular dopamine in comparison to wildtype animals. Further work includes the examination of raclopride to increase extracellular dopamine, selective serotonin reuptake inhibitors to monitor serotonin, and desipramine to measure norepinephrine dynamics. This study allows for the further investigation of the neurochemical and behavioral effects of hyperglycemia in zebrafish. Future work will extend to the analysis of other monoamines such as serotonin and other dopamine metabolites. Support or Funding Information NIH STTR: 1R41NS113702‐01 Raw for the detection of dopamine in zebrafish retina after potassium chloride stimulation.

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Fast scan cyclic voltammetry (FSCV) and carbon-fiber microelectrodes (CFMEs) have been utilized used to detect several important neurochemicals in vivo. However, this method is limited due to the ability to discriminate dopamine from several of its metabolites. Carbon nanotube and polymer modified microelectrodes will be utilized to detect physiologically low levels of neurotransmitters that also resist surface fouling and have high temporal resolution to detect fast changes of neurotransmitters. Furthermore, novel electrode coatings and waveforms will also be utilized to detect several neurotransmitter metabolites such as dopamine, norepinephrine, normetanephrine, 3-methoxytyramine (3-MT), homovanillic acid (HVA), 3,4 dihydroxyphenylacetic acid (DOPAC), and other metabolites. Currently, dopamine is thought to be an important neurotransmitter concerning several disease states such Parkinson’s disease, drug abuse (amphetamine, cocaine, etc.), and even for gambling and sex-disorders. However, dopamine is metabolized on a subsecond timescale, and studies have pointed to the importance of neurotransmitter metabolites in these disease states apart from dopamine. Presently, there is no method to selectively co-detect these neurotransmitter metabolites of dopamine utilizing FSCV. Through several waveform modifications and polymer electrode coatings, we develop a novel method to tune the detection of dopamine and said metabolites, which will help differentiate dopamine and respective metabolites through the shapes and positions of their respective cyclic voltammograms. Preliminary measurements have also been made in zebrafish whole brain ex vivo showing the application of this technique in biological tissue. Discriminating the detection of dopamine from its metabolites will have many implications in better understanding complex disease, behavioral, and pharmacological states.