Optimization of graphene oxide-modified carbon-fiber microelectrode for dopamine detection

Graphene oxide (GO) is a carbon-based material that is easily obtained from graphite or graphite oxide. GO has been used broadly for electrochemistry applications and our hypothesis is that GO coating a carbon-fiber microelectrode (CFME) will increase the sensitivity for dopamine by providing more adsorption sites due to the enhancement of oxygen functional groups. Here, we compared drop casting, dip coating, and electrodeposition methods to directly coat commercial GO on CFME surfaces. Dip coating did not result in much GO coating and drop casting resulted in large agglomerations that produced noisy signals and slow rise times. Electrodeposition method with cyclic voltammetry increase the current for dopamine and this method was the most reproducible and had the least noise compared to the other two coating methods. The optimized method used a triangular waveform scanned from -1.2 V to 1.5 V at 100 mV/s for 5 cycles in 0.2 mg/mL GO in water. With fast-scan cyclic voltammetry (FSCV), the optimized GO/CFME enhanced the dopamine oxidation peak two-fold. The sensitivity of the modified electrode is 41±2 nA/μM with a linear range from 25 nM to 1 μM, and a limit of detection of 11 nM. The optimized electrodes were used to detect electrically-stimulated dopamine in brain slices to demonstrate their performance in tissue. Thus, GO can be used to enhance the sensitivity of electrodes for dopamine and improve biological measurements.