Carbon Nanoelectrodes for the Electrochemical Detection of Neurotransmitters

Abstract

Carbon-based electrodes have been developed for the detection of neurotransmitters over the past 30 years using voltammetry and amperometry. The traditional electrode for neurotransmitter detection is the carbon fiber microelectrode (CFME). The carbon-based electrode is suitable for in vivo neurotransmitter detection due to the fact that it is biocompatible and relatively small in surface area. The advent of nanoscale electrodes is in high demand due to smaller surface areas required to target specific brain regions that are also minimally invasive and cause relatively low tissue damage when implanted into living organisms. Carbon nanotubes (CNTs), carbon nanofibers, carbon nanospikes, and carbon nanopetals among others have all been utilized for this purpose. Novel electrode materials have also required novel insulations such as glass, epoxy, and polyimide coated fused silica capillaries for their construction and usage. Recent research developments have yielded a wide array of carbon nanoelectrodes with superior properties and performances in comparison to traditional electrode materials. These electrodes have thoroughly enhanced neurotransmitter detection allowing for the sensing of biological compounds at lower limits of detection, fast temporal resolution, and without surface fouling. This will allow for greater understanding of several neurological disease states based on the detection of neurotransmitters.

Figure 1:

Figures provided from Venton Lab.

Figure 2:

Scanning electron micrograph (SEM) image of a glass capillary insulated CFME (figures provided from Venton Lab). Figure comes from [27].

Figure 3:

Structure of single wall carbon nanotube (SWCNT).

Figure 4:

Comparison between bare (solid line) and CNT coated (dashed line) disk electrodes. (c) Background subtracted CVs for 2 μM serotonin. (d) Background subtracted CVs for 2 μM serotonin and 5 μM dopamine [17]. Reprinted from [17].

Figure 5:

Current versus time trace depicting 40-fold increase in sensitivity after dipping in CNT suspension to form CNT forest electrode [28]. Reprinted from [28].

Figure 6:

Schematic of wet spinning apparatus setup [29]. Reprinted from [29].

Figure 7:

SEM of PANi-CNT fiber [30]. Reprinted from [30].

Figure 8:

CNT fiber completely sealed by epoxy resin to form CNT-microelectrode [31]. Reprinted with permission from [31].

Figure 9:

Mechanism of CNT fiber formation. (a) SWNTs in van der Waals contact. (b) SWNT ropes after exposure to sulfuric acid [32]. Reprinted from [32].

Figure 10:

SEM of vertically aligned CNT fiber spun with chlorosulfonic acid [33]. Reprinted from [33].

Figure 11:

Representative cyclic voltammograms from electrodes before (dashed lines) and after modification with carbon nanotubes (solid line). Vertical columns compare types of functionalized nanotubes: amide-CNTs (panels (A)–(C)), carboxylic acid-CNTs. Figure reproduced with permission from [16].