We present a method to modify carbon fiber microelectrodes (CFME) with porous carbon nanofibers (PCFs) to improve detection and to investigate the impact of porous geometry for dopamine detection with fast-scan cyclic voltammetry (FSCV). PCFs were fabricated by electrospinning, carbonizing, and pyrolyzing poly­(acrylonitrile)-b-poly­(methyl methacrylate) (PAN-b-PMMA) block copolymer nanofiber frameworks. Commonly, porous nanofibers are used for energy storage applications, but we present an application of these materials for biosensing, which has not been previously studied. This modification impacted the topology and enhanced redox cycling at the surface. PCF modifications increased the oxidative current for dopamine (2.0 ± 0.1)-fold (n = 33) with significant increases in detection sensitivity. PCFs are known to have more edge plane sites which we speculate lead to the 2-fold increase in electroactive surface area. Capacitive current changes were negligible, providing evidence that improvements in detection are due to faradaic processes at the electrode. The ΔE p for dopamine decreased significantly at modified CFMEs. Only a 2.2 ± 2.2% change in dopamine current was observed after repeated measurements and only 10.5 ± 2.8% after 4 h, demonstrating the stability of the modification over time. We show significant improvements in norepinephrine, ascorbic acid, adenosine, serotonin, and hydrogen peroxide detection. Lastly, we demonstrate that the modified electrodes can detect endogenous, unstimulated release of dopamine in living slices of rat striatum. Overall, we provide evidence that porous nanostructures significantly improve neurochemical detection with FSCV and echo the necessity for investigating the extent to which geometry impacts electrochemical detection.

Fundamental insight into the extent to which the nanostructured surface and geometry impacts neurochemical interactions at electrode surfaces could provide significant advances in our ability to design and fabricate ultrasensitive...

We present a novel copolymer-based, uniform porous carbon microfiber (PCMF) formed via wet-spinning for significantly improved electrochemical detection. Carbon fiber (CF), fabricated from a polyacrylonitrile (PAN) precursor, is commonly used in batteries or for electrochemical detection of neurochemicals due to its biplanar geometry and desirable edge plane sites with high surface free energy and defects for enhanced analyte interactions. Recently, the presence of pores within carbon materials has presented interesting electrochemistry leading to detection improvements; however, there is currently no method to uniformly create pores on a carbon microfiber surface impacting a broad range of electrochemical applications. Here, we synthesized controllable porous carbon fibers from a spinning dope of the copolymers PAN and poly(methyl methacrylate) (PMMA) in dimethylformamide via wet spinning for the first time. PMMA serves as a sacrificial block introducing macropores of increased edge-plane character on the fiber. Methods were optimized to produce porous CFs at similar dimensions to traditional CF. We prove that an increase in porosity enhances the degree of disorder on the surface, resulting in significantly improved detection capabilities with fast-scan cyclic voltammetry. Local trapping of analytes at porous geometries enables electrochemical reversibility with improved sensitivity, linear range of detection, and measurement temporal resolution. Overall, we demonstrate the utility of a copolymer synthetic method for PCMF fabrication, providing a stable, controlled macroporous fiber framework with enhanced edge plane character. This work will significantly advance fundamental investigations of how pores and edge plane sites influence electrochemical detection.

Understanding how the brain functions in both spatial and temporal domains is still unknown but vital for advancing knowledge of fundamental brain processes. One important class of brain biomolecules, purines, are involved in signal transduction, development, neuroinflammation, and neuromodulation. Despite their importance, purines remain difficult to detect with high specificity, sensitivity, and with adequate temporal resolution to capture signaling dynamics. Fast-scan cyclic voltammetry (FSCV) at carbon-fiber microelectrodes is a popular electrochemical technique most often used to study dopamine signaling in the brain due to its subsecond temporal resolution and excellent spatial resolution. Recent advances from our lab and others have demonstrated utility of using FSCV at carbon-based electrodes for adenosine and guanosine detection: two important purine signaling molecules in the brain. Despite these advances, a fundamental understanding of purine electrochemical detection at carbon-based electrodes is poorly understood, especially for anionic purinergic compounds like adenosine triphosphate (ATP) and guanosine triphosphate (GTP). Here, we will discuss our recent work which helps describe the extent to which the electrode surface chemistry, topographical structure, and geometry impact purine detection with FSCV. This work will ultimately lead to more sensitive and selective detection of purinergic signaling in the brain. Carbon-fibers have been a prominent electrode material for neurochemical detection with fast-scan cyclic voltammetry (FSCV) for the last several decades. Recently, the field has expanded to novel carbon nanomaterials due to their improved detection sensitivities and electron transfer kinetics. Despite, exploration to novel carbon materials, the majority of FSCV labs still use carbon-fiber microelectrodes on a routine basis for neurochemical analysis. Because of this, our lab has focused on tuning analyte-electrode interactions at carbon-fiber microelectrodes using a combination of surface modification strategies and novel carbon-fiber materials. We will discuss our latest efforts to improve purine detection with novel carbon surfaces. Plasma-treated carbon surfaces can dramatically change the functionality and topology of the surface. We have used O2, N2, and Ar gas to change the surface topology and functionality of carbon-fiber microelectrodes for improved purine detection. Overall, we show that the effects induced by plasma-treatment improve purine detection significantly more than catecholamine detection due to significantly roughened electrode surfaces with increased oxide and amine functionalization. In addition to plasma-treated surfaces, the chemical composition of the carbon-fiber surface can be modified by chemically reacting specific functionalities onto the surface. Traditionally, anionic detection with FSCV is limited due to minimal interactions of anions on the anionic carbon-fiber surface. We have used a chemical modification strategy involving both ethylenediamine (EDA) and N-ethyl-N’-(3-dimethylaminopropyl) carbodiimide (EDC) to functionalize the carbon-fiber surface with positively charged amines. In addition to chemical functionalization strategies for improved anionic purine detection, we have also investigated Au and Pt nanoparticle modified carbon-fibers for improved electrocatalysis of purines at the surface. Lastly, we have synthesized and developed new carbon-fiber geometries with improved edge-plane character on the surface which facilitate enhanced purine-electrode interactions. Overall, we provide new insights into the electrode-analyte interface for purine detection which has significantly improved our understanding of purine electrochemistry.