Synthesis of ZIF-8/g-C₃N₄/SiO₂ photoresponsive nanozyme and its application for colorimetric detection of ascorbic acid.

Given the vital nutritional and metabolic role of ascorbic acid (AA) and the need for rapid detection, a photoresponsive nanozyme-based composite was developed for sensitive, accurate, and convenient AA analysis. In this report, a ternary ZIF-8/g-C3N4/SiO2 photoresponsive oxidase-mimicking system was developed and applied to AA detection. By regulating the loading ratio of ZIF-8 on the g-C3N4/SiO2 substrate, the composite with excellent photoresponsive oxidase-like activity was successfully prepared. Owing to its enhanced visible-light absorption and efficient charge separation and transfer, the system exhibited significantly improved photoresponsive performance. Experimental results demonstrated that ZIF-8/g-C3N4/SiO2 could catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB), generating oxidized TMB (oxTMB) through the formation of reactive species, thereby producing a distinct color change. In an acidic environment, AA inhibited the oxidase-like activity of the catalyst due to its strong reducing capability, thus suppressing the colorimetric reaction. Based on this principle, the as-synthesized ZIF-8/g-C3N4/SiO2 photoresponsive oxidase mimic was applied to the detection of AA in three beverages. The method revealed a good linear response within the concentration range of 1-40 μM, and the detection limit (LOD) was 0.14 μM. The recoveries of the spiked samples ranged from 95.00% to 103.85%, suggesting that the present method could be successfully applied to sense AA in practical samples. Furthermore, we integrated ZIF-8/g-C3N4/SiO2 with the RGB strategy into a novel sensing platform for the visual/onsite semi-quantitative detection of AA in real samples, demonstrating the great potential prospects for the development of rapid food assay.