We present the first electrochemical characterization of guanosine, a purinergic neuromodulator and neuroprotector, using fast-scan cyclic voltammetry at carbon-fiber microelectrodes.

Guanosine and adenosine are important neuromodulators in the brain and work in cooperation to mitigate the effects of stroke, traumatic injury, and other neurological events. Both purines can act on slow (minutes to hours) and rapid (milliseconds to seconds) time scales. A guanosine–adenosine interaction has been proposed in which guanosine modulates adenosine levels, and the two work together to control glutamate neurotransmission. Traditional methods to codetect purines, such as HPLC with microdialysis, are robust but lack the temporal resolution necessary to quantify release in real time. Fast-scan cyclic voltammetry (FSCV) has been used to detect guanosine and adenosine independently, but codetection has not been possible. Here, we developed a novel “scalene waveform” to codetect guanosine and adenosine with nanomolar limits of detection in real time with FSCV. The scalene waveform uses a slow rate (100 V/s) on the forward scan and the conventional rate (400 V/s) on the back scan; potentials go from −0.4 to 1.45 V and back to −0.4 V. The scan rates were optimized to increase the separation of the oxidative peaks for guanosine and adenosine. The temporal separation of the primary peaks was increased (4.6 ± 0.1)-fold at the scalene waveform compared to the traditional waveform. Both exogenously applied guanosine and adenosine and endogenous transient release were detected at the scalene waveform in rat-brain slices. We show the first method for codetecting guanosine and adenosine using FSCV, which can be used to study the guanosine–adenosine interaction and better understand their cooperative therapeutic effects.

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.