An innovative paper-based dual-mode sensor integrating fluorescence and colorimetry for sensitive detection of quercetin via CeO2@UiO-66-NH2 nanozyme.

Quercetin, a potent natural antioxidant, is gaining widespread attention for its remarkable health benefits, including the prevention of cardiovascular diseases, allergies, diabetes, and cancer. As a promising functional food ingredient, there is an urgent need for fast, sensitive, and portable methods to monitor quercetin levels in various products. In this study, we present a portable dual-mode nanozyme-driven sensor based on cerium dioxide nanoparticle-anchored metal-organic framework (CeO2@UiO-66-NH2) nanocomposite. This nanocomposite exhibits impressive oxidase-like activity and intrinsic fluorescence properties, enabling it to catalyze the oxidation of colorless N, N-diethyl-p-phenylenediamine to a pink product, which in turn quenches the fluorescence of CeO2@UiO-66-NH2 at 458 nm via an inner filter effect (IFE). The presence of quercetin inhibits reactive oxygen species generation, thus attenuating the oxidation and restoring fluorescence. A paper-based fluorescent-colorimetric dual-mode sensing platform was established for quercetin detection, enabling rapid and visual evaluation without complex instruments. The proposed method exhibited a broad linear response range of 1-60 μM. The limits of detection for the colorimetric/fluorescent and paper-based colorimetric/fluorescent were 0.35, 0.27, 0.37, and 0.29 μM, respectively. This dual-mode sensor demonstrates excellent analytical sensitivity and selectivity, with successful application in real vegetable and juice samples, offering a reliable, efficient tool for quercetin monitoring in food and functional food ingredients.