Galvanic Redox Potentiometry for Self-Driven in Vivo Measurement of Neurochemical Dynamics at Open-Circuit Potential

Understanding the real-time correlation between chemical patterns and neural processes is critical for deciphering brain function. Voltammetry has enabled this task but with a number of challenges for current-based electrolysis in vivo. Herein, we report galvanic redox potentiometry (GRP) potentially as a universal strategy for in vivo monitoring of neurochemicals, with ascorbic acid (AA) as a typical example. The GRP sensor is constructed on a self-driven galvanic cell configuration, where AA is spontaneously oxidized at the indicating single-walled carbon nanotube-modified carbon fiber electrode (SWNT-CFE), while oxygen reduced at the laccase-modified reference CFE (Lac-CFE). At thermodynamic equilibrium, open-circuit potential (OCP) can be a linear indicator of the concentration of AA. The resulting sensor shows a high selectivity to AA dynamics in the presence of coexisting electroactive neurochemicals, which is mainly determined by the driving force for the cell reaction, as suggested by principal investigation. Sensing sensitivity of this OCP-based GRP method is not affected by nonspecific protein adsorption and electrode fouling. Moreover, a micropipette compartment of the reference electrode is designed to suppress mass crossover and prevent disturbance to oxygen reduction through confinement effect. The in vivo application of the GRP sensor is illustrated by measuring the basal level of cortical AA in live rat brain (230 +/- 40 mu M) and its dynamics during ischemia/reperfusion. The GRP concept is demonstrated as a prominent method for in vivo, real-time, quantitative analysis of brain neurochemistry.