Colorimetric detection of total antioxidants in green tea with oxidase-mimetic CoOOH nanorings

Green tea is a popular beverage and is widely consumed due to its taste and antioxidative polyphenols. Herein, a smartphone-based colorimetric reader using cobalt oxyhydroxide (CoOOH) nanorings has been successfully applied to detect antioxidants in green tea with high reliability and robustness. By exploiting the oxidase-mimicking activity, the as-synthesized CoOOH nanorings replaces natural enzymes to directly catalyze oxidate colorless 3,3 ´ ,5,5 ´ -tetramethylbenzidine (TMB), while antioxidants can disintegrate CoOOH, leading to an antioxidant concentration-dependent color change. Benefiting from the CoOOH nanorings-based colorimetric strategy, a smartphone-assistant nanosensor was devised for portable and visual detection of antioxidants in green tea. The proposed method can be extended to visual detection of a diverse range of diseases by responding to their specific antioxidant, and thus provide a pivotal disease toolbox that is compatible for development at the point-of-care.