Rapid identification of Longjing tea from different scale origins by a colorimetric sensor based on the oxidase-like activity of Cu-CDs

s As a typical national product of geographical indication in China, the provenance of Longjing tea exerts a significant influence on its quality and market value. This study presents a smart and fast colorimetric sensor based on the oxidase-like activity of copper-doped carbon dots (Cu-CDs) for the discrimination of Longjing tea origin and grade at different scales. Based on the differences in catechin content among Longjing teas from different origins and grades, the sensor utilizes the differential restoring capacities of catechins to amplify the characteristic differences between tea samples. Upon introduction of the Cu-CDs sensing system, its oxidase-like activity catalyzes redox reactions between tea catechins and TMB, inducing observable color changes through modulation of particle surface charge distribution and aggregation states. By extracting RGB values from color images and integrating PLS-DA and RF chemometric models, this study can not only quickly and accurately identify the types and contents of eight catechins, but also visually distinguish the origin and grade of Longjing tea. The discrimination accuracy rate for both the training set and the prediction set reached 100.00%. This method has been shown to facilitate rapid on-site testing, thereby providing an effective means of swiftly identifying the origin of Longjing tea.