Os–Ru nanozyme with peroxidase-mimicking activity for rapid dual-readout colorimetric analysis of catechins in green tea beverages

Catechin, a phenolic-active substance extracted from natural plants, exhibits a wide range of biological activities. However, exceeding safe levels can harm human health, making accurate quantification essential. Current assay methods, however, do not provide efficient or precise catechin measurements. In this study, an Os-Ru nanozyme with outstanding peroxidase-mimicking activity was first developed, showing <i>K</i> _m values of 0.36 mM for 3,3',5,5'-tetramethylbenzidine (TMB) and 2.67 mM for H₂O₂. Additionally, catechin was found to effectively scavenge hydroxyl radicals (HO˙) generated from H₂O₂ decomposition by the Os-Ru nanozyme. Based on this, a rapid dual-readout colorimetric method for catechin detection was established, featuring an absorbance measurement in solution and grayscale (G) analysis on a paper platform, both based on the Os-Ru nanozyme. This dual-readout colorimetric method achieved highly sensitive catechin detection across a broad linear concentration range (0 to 450 μmol L^-1), with detection limits of 2.84 μmol L^-1 for absorbance measurement and 9.68 μmol L^-1 for the <i>G</i> value analysis. Moreover, the method demonstrated excellent reliability and accuracy in practical applications, yielding spiked recoveries between 91.78 and 103.01% and relative standard deviations (RSD) ranging from 1.62 to 6.74% in the analysis of green tea beverages. Overall, this Os-Ru nanozyme-based dual-readout colorimetric method has considerable potential for practical catechin detection and could provide additional inspiration and ideas for the rational design and development of colorimetric sensing methods for rapid detection of nanozyme-based antioxidants.