Beyond single-mechanism: A three-channel MnO2 nanozyme array for point-of-care flavonoid isomers discrimination and proof-of-concept Citrus differentiation.

The rapid differentiation of closely related Citrus plants remains a challenge due to their highly similar physicochemical profiles. This study developed a three-channel colorimetric sensor array based on morphologically distinct MnO2-I/II/III nanozymes with diverse oxidase-like activity. Synergistic free radical scavenging and electron transfer during catalysis induce specific absorbance changes of TMB/oxTMB (green, yellow, and blue) at 370, 450, and 652 nm, which may be synergistically mediated by flavonoid structures and coordination interactions. The multi-mechanism three-channel design provides a highly cross-reactive dataset on a paper-based platform, enabling HCA, PCA, and 3D LDA to: (i) discriminate flavonoid isomers (1-500 μg/mL), (ii) identify adulterated samples (0-100%), and (iii) achieve 100% accuracy on an independent test set for multi-batch Citrus samples. This work presents a mechanism-distinctive MnO2 nanozyme array, which, coupled with chemometric analysis, serves as a promising proof-of-concept platform for point-of-care screening of structurally similar flavonoids and closely related plant samples.