High Antifouling Property of Ion-Selective Membrane: toward In Vivo Monitoring of pH Change in Live Brain of Rats with Membrane-Coated Carbon Fiber Electrodes

In vivo monitoring of pH in live brain remains very essential to understanding acid–base chemistry in various physiological processes. This study demonstrates a potentiometric method for in vivo monitoring of pH in the central nervous system with carbon fiber-based proton-selective electrodes (CF-H+ISEs) with high antifouling property. The CF-H+ISEs are prepared by formation of a H+-selective membrane (H+ISM) with polyvinyl chloride polymeric matrixes containing plasticizer bis(2-ethylhexyl)sebacate, H+ ionophore tridodecylamine, and ion exchanger potassium tetrakis(4-chlorophenyl)borate onto carbon fiber electrodes (CFEs). Both in vitro and in vivo studies demonstrate that the H+ISM exhibits strong antifouling property against proteins, which enables the CF-H+ISEs to well maintain the sensitivity and reversibility for pH sensing after in vivo measurements. Moreover, the CF-H+ISEs exhibit a good response to pH changes within a narrow physiological pH range from 6.0 to 8.0 in quick response time with high reversibility and selectivity against species endogenously existing in the central nervous system. The applicability of the CF-H+ISEs is illustrated by real-time monitoring of pH changes during acid–base disturbances, in which the brain acidosis is induced by CO2 inhalation and brain alkalosis is induced by bicarbonate injections. The results demonstrate that brain pH value rapidly decreases in the amygdaloid nucleus by ca. 0.14 ± 0.01 (n = 5) when the rats breath in pure CO2 gas, while increases in the cortex by about 0.77 ± 0.12 (n = 3) following intraperitoneal injection of 5 mmol/kg NaHCO3. This study demonstrates a new potentiometric method for in vivo measurement of pH change in the live brain of rats with high reliability.