Ratiometric Electrochemical Sensor for Effective and
Reliable Detection of Ascorbic Acid in Living Brains
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Abstract
The <i>in vivo</i> detection of ascorbic acid (AA), one
of the physiologically important cerebral neurochemicals, is critical
to probe and understand brain functions. Electrochemical sensors are
convenient for AA detection. However, conventional electrochemical
sensors usually suffer from several challenges, such as sluggish electron
transfer kinetics for AA oxidation and poor reproducibility. To address
these challenges, here we report ratiometric electrochemical sensors
for effective and reliable detection of AA in living brains. The sensors
were constructed by immobilizing preassembled thionine/Ketjen black
(KB) nanocomposites onto glassy carbon (GC) electrodes or carbon fiber
microelectrodes (CFMEs). The KB in the rationally functionalized nanocomposites
efficiently facilitated AA oxidation at a relatively negative potential
(∼−0.14 V) without particular physical or chemical pretreatment,
forming the basis of selective measurement of AA. With a well-defined
and reversible pair of redox wave at −0.22 V, the assembled
thionine acted as an internal reference to substantially alleviate
the lab-to-lab, person-to-person, and electrode-to-electrode variations.
The <i>in vitro</i> experiments demonstrated that the sensors
exhibited extremely high reproducibility and stability toward selective
measurement of AA. More, with operational simplicity and robustness
in analytical performance, the designed sensors were successfully
applied to <i>in vivo</i> effectively, selectively, and
reliably monitor the dynamic change of cerebral AA associated with
pathological processes (i.e., salicylate-induced tinnitus as the model)
in living rats’ brains. This study not only offers a new strategy
for construction of ratiometric electrochemical sensors but also opens
a new way for selective and reliable detection of neurochemicals for
probing brain functions