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

Abstract

Carbon fiber microelectrodes (CFMEs) have been extensively used to measure neurotransmitters with fast-scan cyclic voltammetry (FSCV) due to their ability to adsorb cationic monoamine neurotransmitters. Although FSCV, in tandem with CFMEs, provides high temporal and spatial resolution, only single-channel potentiostats and electrodes have been primarily utilized. More recently, the need and use of carbon fiber multielectrode arrays has risen to target multiple brain regions. Previous studies have shown the ability to detect dopamine using multielectrode arrays; however, they are not readily available to the scientific community. In this work, we interfaced a carbon fiber multielectrode array (MEA or multielectrode array), to a commercially available four-channel potentiostat for multiplexing neurochemical measurements. The MEA's relative performance was compared to single CFMEs where dopamine detection was found to be adsorption controlled to the electrode's surface. Multiple waveforms were applied to each fiber of the multielectrode array simultaneously to detect different analytes on each electrode of the array. A proof of concept ex vivo experiment showed that the multielectrode array could record redox activity in different areas within the mouse caudate putamen and detect dopamine in a 3-mm² area. To our knowledge, this is the first use of the multielectrode array paired with a commercially available multichannel potentiostat for multi-waveform application and neurotransmitter co-detection. This novel array may aid in future studies to better understand complex brain heterogeneity, the dynamic neurochemical environment, and how disease states or drugs affect separate brain areas concurrently. Graphical abstract.

Keywords: Carbon fiber; FSCV; Microelectrodes; Neurotransmitters.

Fig. 1

(a) The multielectrode array taken by a Samsung camera (Samsung Note 20 Ultra, 108-MP wide-angle camera). Approximate scale bar is shown. (b) The four carbon fibers of the multielectrode array viewed under a light microscope, at 20× magnification. (c) SEM image of a single fiber of the multielectrode array with a 10-μm scale bar. The carbon fiber (black) protrudes out, and the white insulating material is the Parylene C coating. (d) Connection schematic of multielectrode array showing the separate pieces of hardware that is required for adapting it to a commercial potentiostat. See ESM Fig. S1 for setup and parts photos

Fig. 2

Cyclic voltammograms (CVs) of the a CFME compared to the b 4 channels of the multielectrode array overlaid on one another. The CVs indicated no differences in the peak oxidative current of the electrodes for dopamine detection. c Bar graph showing no statistical significance (NS) between peak oxidative current. Standard error of the mean used for error bars. (N = 3 for each electrode type)

Fig. 3

Comparison of a CFME to c multielectrode array showing the linear relationship of normalized current versus increasing scan rate ranging from 50 to 1000 V/s. Peak oxidative current was found to be linearly dependent and proportional to scan rate. Stability experiments of b CFME and d multielectrode array over the course of 4 h showed no significant difference in peak oxidative current over time. Error bars are shown as standard error of the mean. (N = 3 for each electrode type)

Fig. 4

Dopamine concentration curve ranging from 1 to 100 μM for the a CFME and c multielectrode array, highlighting the lower concentration linear relationship of the CFME (b) and multielectrode array (d). Error bars are shown as standard error of the mean (N = 3 for each electrode type)

Fig. 5

Multiple waveform applications onto the multielectrode array. a Oscilloscope of waveforms applied onto each multielectrode array channel and b the waveform shapes: triangle, Jackson, extended, and hold. c Overlay of waveforms applied onto the multielectrode array and the oscilloscope of channels 1–4. Channel 1 corresponds to the DA triangle waveform. Channel 2 is applied with the 5-HT Jackson waveform. Channel 3 displays the 5-HT extended waveform, and channel 4 shows the 5-HT extended hold waveform, as seen in the legend on the right-hand side of c

Fig. 6

Multi-waveform detection of serotonin where each channel corresponds to the applied waveform for 5-HT detection as seen in the legend (triangle, Jackson, extended, and hold). The oscilloscope signals seen in Fig. 5 correspond to the shape of the electrode

Fig. 7

Co-detection of DA, 5-HT, and adenosine (Adn) using their respective waveforms and with varying concentration ratios. a DA was co-detected using the DA triangle waveform on channel 1 with increasing concentrations from 100 nM to 10 μM and in a mixture of 100 nM 5-HT and 10 μM adenosine. Asterisks in a and b indicate artifact signal from the adenosine analyte. b 100 nM to 1 μM 5-HT was co-detected using the EWF on channel 2 and the c EHWF on channel 3 with 1 μM DA and 10 μM adenosine. d Adenosine was co-detected from 1 to 10 μM in a mixture of 100 nM 5-HT and DA, each, on channel 4 using the triangle waveform

Fig. 8

a The cyclic voltammograms of neurotransmitter release stimulated by the application of KCl ex vivo of the MEA. CVs of channel 1 (b), channel 2 (c), channel 3 (d), and channel 4 (e) that were measured in the brain slice. f The multielectrode array targeted the caudate putamen or dorsal striatum, as indicated by the black circle [53]. The mouse brain atlas was adapted from Allen Mouse Brain Atlas (2004) and the Franklin and Paxinos Atlas [34, 35]. Neurotransmitter release was elicited by applying 1 μL of 0.1 M KCl and a full schematic of the apparatus can be seen in ESM Fig. S5