Novel “On–Off” Colorimetric Sensor for Glutathione Based on Peroxidase Activity of Montmorillonite-Loaded TiO2 Functionalized by Porphyrin Precisely Controlled by Visible Light

Well-dispersed nanocomposites based on Ca-montmorillonite decorated by porphyrin-functionalized titanium dioxide (H2TCPP–TiO2–MMT) were synthesized by a facile strategy. H2TCPP–TiO2–MMT was demonstrated to possess the intrinsic peroxidase-like activity and could catalyze 3′,3′,5′,5′-tetramethylbenzidine (TMB) oxidized by H2O2 accompanied with the color change from colorless to blue in a short time under visible light irradiation. The optimum experimental conditions, robustness, as well as Michaelis–Menten kinetics were investigated. The fluorescent probe assay indicated that the good performance of H2TCPP–TiO2–MMT was attributed to the •OH radicals from H2O2 decomposition, which was induced by the electron–hole pairs of H2TCPP–TiO2–MMT generated under visible light irradiation. Based on its peroxidase activity, a convenient colorimetric sensor for detecting glutathione (GSH) was proposed. The detection limit for GSH was 0.057 μM, with the linear detection range of 0.1–20 μM. Notably, besides the enhanced peroxidase-like activity, another merit for this sensor was that the reaction time can be controlled accurately by adjusting irradiation time compared to traditional colorimetric sensors, which would benefit the accuracy in detecting GSH. In addition, results of anti-interference and detecting GSH in human serum assays indicated that the H2TCPP–TiO2–MMT was predicted to be one of the promising materials for fast visual colorimetry.