Light-responsive cobalt-doped graphitic carbon nitride nanozyme for the colorimetric detection of acetylcholinesterase and its inhibitor.

The rational design of nanozymes with remarkable catalytic activity remains pivotal for advancing colorimetric biosensing platforms. Graphitic carbon nitride (g-CN) has emerged as a captivating photocatalytic material given its cost-effectiveness, ease of fabrication and outstanding stability. However, its practical implementation as a light-responsive nanozyme is fundamentally constrained by suboptimal catalytic activity. Herein, cobalt was incorporated into g-CN nanosheets, giving rise to the formation of cobalt-doped graphitic carbon nitride nanosheets (Co/g-CN), which significantly enhanced its light-responsive oxidase-mimicking activity primarily attributed to its notably enhanced visible light absorption capacity and optimized photo-generated charge carrier separation/transfer efficiency. When exposed to visible light illumination, Co/g-CN triggered the chromogenic reaction by facilitating the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) owing to the generation of hydrogen oxide, singlet oxygen and photogenerated holes. Furthermore, capitalizing on the inhibitory effect of thiocholine on the TMB oxidation, a new colorimetric method was established to determine acetylcholinesterase (AChE) activity. This colorimetric method enabled determination of AChE activity ranging from 0.1-15 mU/mL, achieving a remarkably low detection limit of 0.04 mU/mL. Moreover, it was effectively utilized to ascertain AChE activity in serum samples with desirable results. Additionally, it was successfully applied to detect AChE inhibitor. This work not only advances the modulation of catalytic activities in light-responsive nanozymes, but also presents an innovative perspective for AChE activity determination.