Waste Coffee Ground-Derived Porous Carbon for Neurochemical Detection.

We present an optimized synthetic method for repurposing coffee waste to create controllable, uniform porous carbon frameworks for biosensor applications to enhance neurotransmitter detection with fast-scan cyclic voltammetry. Harnessing porous carbon structures from biowastes is a common practice for low-cost energy storage applications; however, repurposing biowastes for biosensing applications has not been explored. Waste coffee ground-derived porous carbon was synthesized by chemical activation to form multivoid, hierarchical porous carbon, and this synthesis was specifically optimized for porous uniformity and electrochemical detection. These materials, when modified on carbon-fiber microelectrodes, exhibited high surface roughness and pore distribution, which contributed to significant improvements in electrochemical reversibility and oxidative current for dopamine (3.5 ± 0.4-fold) and other neurochemicals. Capacitive current increases were small, showing evidence of small increases in electroactive surface area. Local trapping of dopamine within the pores led to improved electrochemical reversibility and frequency-independent behavior. Overall, we demonstrate an optimized biowaste-derived porous carbon synthesis for neurotransmitter detection for the first time and show material utility for viable neurotransmitter detection within a tissue matrix. This work supports the notion that controlled surface nanogeometries play a key role in electrochemical detection.

Nanostructured carbon-fiber surfaces for improved neurochemical 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 neurochemical detection probes. Here, we investigate the extent to which the nanostructure of the carbon-fiber surface impacts detection of catecholamines and purines with fast-scan cyclic voltammetry (FSCV). Carbon-fibers were treated with argon (Ar) plasma to induce variations in the nano- and micro-structure without changing the functionalization of the surface. We tested variations in topology by measuring the extent to which the flow rate, RF power, and treatment time affect the surface roughness. Flow rates from 50-100 sccm, plasma power from 20-100 W, and treatment times from 30 s to 5 min were compared. Two Ar-treatments were chosen from the optimization studies for comparison, and the surface roughness was evaluated using atomic force microscopy (AFM). To ensure no changes in chemical composition, fibers were analyzed with X-ray photoelectron spectroscopy (XPS). On average, at the optimized Ar-plasma treatment procedure, oxidative current for adenosine and ATP increased by 3.5 ± 1.4-fold and 3.2 ± 0.6-fold, and guanosine and GTP by 1.7 ± 0.3-fold and 1.8 ± 0.3-fold, respectively (n = 9). Dopamine increased by 1.7 ± 0.3-fold. The extent to which changes in the electrode structure impact adsorption, sensitivity, and electron transfer rates were measured. A COMSOL Multiphysics simulation was developed to enable the modeling of mass transport of electroactive species at varying electrode geometries. Overall, this study provides critical insight into the extent to which the nanostructure of the surface impacts the electrochemical detection of neurochemicals.