Boosting manganese dioxide nanozyme activity with sulfur quantum dots for colorimetric and smartphone-based detection of tannic acid.

Excessive tannic acid (TA) is harmful to human health and the environment, underscoring the need for efficient monitoring platforms. This work developed a sulfur quantum dots (SQDs)/MnO nanocomposite as a high-activity nanozyme for TA detection. The SQDs/MnO hybrid exhibits enhanced specific surface area and nanozyme activity, showing a low Michaelis-Menten constant (0.117 mM) toward 3,3',5,5'-tetramethylbenzidine (TMB) and high catalytic affinity. The research findings indicate that SQDs/MnO catalyzes the generation of hydroxyl radicals (•OH) from oxygen. The resulting •OH further oxidizes colorless TMB into blue oxidized TMB (oxTMB). However, in the presence of TA, the generated •OH radicals are captured, thereby reducing the concentration of •OH available for catalyzing TMB. This result prevents the solution from turning blue. Based on this mechanism, a dual-mode analytical platform was established using colorimetric and smartphone-assisted methods, enabling accurate TA detection in complex food and environmental samples. A reliable sensing platform is established through this strategy, enabling food safety surveillance and environmental monitoring.