Ratiometric Electrochemical Sensor for Effective and\nReliable Detection of Ascorbic Acid in Living Brains

Abstract

The <i>in vivo</i> detection of ascorbic acid (AA), one\nof the physiologically important cerebral neurochemicals, is critical\nto probe and understand brain functions. Electrochemical sensors are\nconvenient for AA detection. However, conventional electrochemical\nsensors usually suffer from several challenges, such as sluggish electron\ntransfer kinetics for AA oxidation and poor reproducibility. To address\nthese challenges, here we report ratiometric electrochemical sensors\nfor effective and reliable detection of AA in living brains. The sensors\nwere constructed by immobilizing preassembled thionine/Ketjen black\n(KB) nanocomposites onto glassy carbon (GC) electrodes or carbon fiber\nmicroelectrodes (CFMEs). The KB in the rationally functionalized nanocomposites\nefficiently facilitated AA oxidation at a relatively negative potential\n(∼−0.14 V) without particular physical or chemical pretreatment,\nforming the basis of selective measurement of AA. With a well-defined\nand reversible pair of redox wave at −0.22 V, the assembled\nthionine acted as an internal reference to substantially alleviate\nthe lab-to-lab, person-to-person, and electrode-to-electrode variations.\nThe <i>in vitro</i> experiments demonstrated that the sensors\nexhibited extremely high reproducibility and stability toward selective\nmeasurement of AA. More, with operational simplicity and robustness\nin analytical performance, the designed sensors were successfully\napplied to <i>in vivo</i> effectively, selectively, and\nreliably monitor the dynamic change of cerebral AA associated with\npathological processes (i.e., salicylate-induced tinnitus as the model)\nin living rats’ brains. This study not only offers a new strategy\nfor construction of ratiometric electrochemical sensors but also opens\na new way for selective and reliable detection of neurochemicals for\nprobing brain functions.