Tea in color: Single-probe nanozyme array for multichannel visual fingerprinting and portable quality evaluation

Green tea is valued both for its distinctive flavor and its high levels of bioactive polyphenols. As consumer interest in product authenticity and quality continues to grow, there is a pressing need for simple and reliable methods to evaluate tea quality in a practical setting. In this work, we developed a colorimetric sensor array based on a single chromogenic probe, 3,3',5,5'-Tetramethylbenzidine (TMB), for discriminating tea polyphenols and assessing green tea quality, including type, freshness, and adulteration. The system employs bimetallic platinum-palladium nanoparticles (B-PtPd_NPs) with high oxidase-mimicking catalytic activity, which enables efficient oxidation of TMB under ambient conditions without additional oxidants. The strong catalytic performance facilitates the generation of distinct absorption peaks at 370, 450, and 650 nm, allowing multi-channel spectral responses that reflect the redox behavior of different tea polyphenols. To enhance portability and practical application, the colorimetric changes were captured via smartphone imaging, and RGB values were extracted for data analysis. Combined with linear discriminant analysis, this approach enabled accurate classification of five major polyphenols, their mixtures, and several green tea samples varying in type and storage history. The system also effectively identified adulterated Biluochun tea. This work demonstrates a robust and user-friendly strategy that integrates nanozyme catalysis and smartphone-based RGB analysis, offering a promising platform for on-site evaluation of tea quality and authenticity.