WO nanosheets with peroxidase-like activity and carbon dots based ratiometric fluorescent strategy for xanthine oxidase activity sensing and inhibitor screening.

The abnormal level of xanthine oxidase (XOD) often causes pathological changes, which are related to a series of diseases. Herein, a novel and sensitive ratiometric fluorescent sensing platform based on WO nanosheets and carbon dots (CDs) was constructed to detect XOD activity for the first time. Under the catalytic oxidation of xanthine by XOD, hydrogen peroxide (HO) was generated. In the presence of HO, WO nanosheets were able to catalyze the oxidation of o-phenylenediamine to generate 2,3-diaminophenazine (DAP) with a yellow fluorescence signal at 570 nm due to its great peroxidase-like activity. The oxidation product DAP was capable of quenching the fluorescence of CDs at 430 nm through the inner filter effect. Therefore, the fluorescence intensity ratio F/F can be used for quantitative analysis of XOD activity. This assay displayed good linear relationships in the range of 0.005-0.05 U/L and 0.5-40 U/L with a detection limit of 0.002 U/L. In addition, this ratiometric fluorescent sensing platform was successfully applied to the determination of XOD in human serum samples and XOD inhibitor screening, demonstrating significant potential in disease diagnosis and drug-screening applications.