A colorimetric nanozyme sensor array for authentic discrimination of geographical origin and storage age of Citri...

Tangerine peel, known as Citri reticulatae pericarpium (CRP), is a well-documented medicinal and food-homologous material. CRP has garnered significant global attention due to its versatile properties and proven bioactivities. However, the price and pharmacological activity of CRP vary significantly depending on its geographical origin and storage age. Therefore, it is essential to develop a fast and simple discrimination method for CRP authentication. In this study, a Cu@ZIF-67 nanozyme featuring excellent laccase-like (LAC) and peroxidase-like (POD) activities was successfully fabricated via a mild etching strategy. Enzymatic activity assays revealed that the optimal dual enzymatic activities were achieved at a Cu²⁺ concentration of 175 mM. By leveraging the distinct multi-wavelength signal responses (370 nm, 652 nm, and 504 nm) generated from the catalytic oxidation of TMB, 4-AP, and 2,4-DP, respectively, a multi-wavelength three-channel sensing array was constructed. Mechanistic investigations indicated that the five flavonoids present in CRP exhibit competitive inhibition toward TMB oxidation, whereas they display non-competitive inhibition toward the oxidation of 4-AP and 2,4-DP. This divergence resulted in significant differences in inhibitory effects between the peroxidase-like and laccase-like channels. By integrating Linear Discriminant Analysis (LDA), precise qualitative discrimination of the five flavonoids was realized. Furthermore, a concentration-independent model based on the K-Nearest Neighbors (KNN) algorithm was established, enabling the accurate geographical authentication of CRP samples from 21 cities in 8 provinces and the reliable discrimination of samples with six different storage ages. Thus, this colorimetric sensor array-based strategy offers a rapid and low-cost tool for authenticating CRP, ensuring its quality control.