Multiplexing Neurochemical Detection Using Carbon Electrodes and Fast Scan Cyclic Voltammetry
Authors: Zestos Alexander George , Wonnenberg Pauline M , Liu Favian Alberto , Asrat Thomas Michael 
Published: May 2020

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. PEDOT, Nafion, and Polyethyleneimine 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 retina showing the application of this technique in biological tissue. The co-detection and differentiation of dopamine metabolites and dopamine will have many implications in better understanding complex disease, behavioral, and pharmacological states.
Moreover, within the greater neuroscience community, there has long been a critical need for the development of versatile and affordable multichannel sensors for the detection of neurotransmitters. Little success has been achieved in developing and commercializing these multielectrode arrays used specifically for the detection of neurotransmitters with voltammetry in multiple brain regions.
The brain is by far the most heterogeneous organ, and it is critically important to monitor various brain regions simultaneously in order to understand complex pharmacological, drug, and behavioral states. For example, several studies have shown significant differences in electrical activity and neurotransmitter concentrations in disparate brain regions such as the striatum, hippocampus, and prefrontal cortex among others. Therefore, it is critically important to make high temporal resolution neurochemical measurements to study the phasic firing of neurons in several brain regions concurrently. FSCV allows for high temporal measurements (< 100 msec) of neurotransmitter levels. Some of the many applications of this technique could be measuring neurochemical changes during epileptic seizures with simultaneous EEG measurements in rodents, drug abuse studies, measuring robust dopamine increases during deep brain stimulation in Parkinsonian models, and possibly many others.
This work will also discuss the development of multielectrode arrays (MEAs) for neurotransmitter detection with fast scan cyclic voltammetry in multiple brain regions simultaneously. Parylene and silicon insulated carbon fiber microelectrode arrays were shown to be able to measure neurochemicals in multiple brain regions simultaneously when coupled with multichannel potentiostats. Moreover, we have utilized techniques such as plasma enhanced chemical vapor deposition (PECVD) to deposit conductive carbon nanospikes onto the surface of existing metal multielectrode arrays to give them dual functionality as neurotransmitter sensors with FSCV in addition to being used primarily for electrical stimulation and recording. Other assays have shown the utility of electrodepositing carbon nanotubes and polymers such as PEDOT to coat metal arrays with carbon to give them dual sensing capabilities. This BRAIN Initiative funded work will allow us to further understand complex brain heterogeneity by making measurements in multiple brain regions simultaneously.