Amine-functionalized carbon-fiber microelectrodes for enhanced ATP detection with fast-scan cyclic voltammetry.

Here, we provide evidence that functionalizing the carbon-fiber surface with amines significantly improves direct electrochemical adenosine triphosphate (ATP) detection with fast-scan cyclic voltammetry (FSCV). ATP is an important extracellular signaling molecule throughout the body and can function as a neurotransmitter in the brain. Several methods have been developed over the years to monitor and quantitate ATP signaling in cells and tissues; however, many of them are limited in temporal resolution or are not capable of measuring ATP directly. FSCV at carbon-fiber microelectrodes is a widely used technique to measure neurotransmitters in real-time. Many electrode treatments have been developed to study the interaction of cationic compounds like dopamine at the carbon surface yet studies investigating how to improve anionic compounds, like ATP, at the carbon fiber surface are lacking. In this work, carbon-fibers were treated with N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) which reacts with carboxylic acid groups on the carbon surface followed by reaction with ethylenediamine (EDA) to produce NH2-functionalized carbon surfaces. Overall, we a 5.2 ± 2.5-fold increase in ATP current with an approximately 9-fold increase in amine functionality, as analyzed by X-ray Photoelectron Spectroscopy, on the carbon surface was observed after modification with EDC-EDA. This provides evidence that amine-rich surfaces improve interactions with ATP on the surface. This study provides a detailed analysis of ATP interaction at carbon surfaces and ultimately a method to improve direct and rapid neurological ATP detection in the future.

Defect Sites Modulate Fouling Resistance on Carbon-Nanotube Fiber Electrodes.

Carbon nanotube (CNT) fiber electrodes have become increasingly popular electrode materials for neurotransmitter detection with fast-scan cyclic voltammetry (FSCV). The unique properties of CNT fiber electrodes like increased electron transfer, sensitivity, waveform application frequency independence, and resistance to fouling make them ideal biological sensors for FSCV. In particular, their resistance to fouling has been observed for several years, but the specific physical properties which aid in fouling resistance have been debated. Here, we investigate the extent to which the presence of defect sites on the surface attenuate both chemical and biological fouling with FSCV. We compared traditional carbon-fiber microelectrodes (CFMEs) to pristine CNTs and functionalized CNTs. CFMEs and functionalized CNTs are highly disordered with a great deal of defect sites on the surface. The pristine CNTs have fewer defects compared to the purposefully functionalized CNTs and CFMEs. All electrode surfaces were characterized by a combination of scanning electron microscopy (SEM), Raman spectroscopy, and energy dispersive spectroscopy (EDS). Chemical fouling was studied using serotonin, a popular neurotransmitter notoriously known for electrode fouling. To assess biological fouling, electrodes were implanted in brain tissue for 2 h. Defect sites on the carbon were shown to resist biofouling compared to pristine CNTs but were detrimental for serotonin detection. Overall, we provide insight into the extent to which the electrode surface dictates fouling resistance with FSCV. This work provides evidence that careful considerations of the surface of the CNT material are needed when designing sensors for fouling resistance.