In Vivo and Online Optical Ascorbic Acid Monitoring in Living Rat Brains Using a Brightfield Microscope-Based Online Detection Platform

Online electrochemical systems (OECSs) possess a distinct continuously monitoring ability toward electro-active species and have been intensively used for single/multiple neurochemical measurements. However, detecting electro-inactive species or some substances being oxidized/reduced at close potentials is difficult in OECS, and it is highly demanded to broaden such useful online methodology to more new principles, which, however, is still lacking. The system reported in this Letter demonstrates a solution to the aforementioned problem. We report an online optical detection platform (OODP) based on visible light absorption for the continuous monitoring of neurochemicals in rat brains with ascorbic acid (AA) as an example. The OODP is constructed with a homemade online capillary-based microfluidic line as the optical detector built under a brightfield microscope. Cobalt oxyhydroxide (CoOOH) nanoflakes directly oxidizing 3,3′,5,5′-tetramethylbenzidine (TMB) into a blue-colored product (oxTMB) which can be faded by AA paves a principle for selective AA recognition. Combined with in vivo microdialysis sampling, an in vivo AA monitoring assay was established by directly integrating this visible light absorption-based probe and the brightfield microscope-based OODP. The OODP for AA measurement possesses excellent stability, reproducibility, a wide linear detection range from 0.5 to 100 μM, and can successfully record the cerebral AA alterations in the clam/ischemia model.