Fluorescence sensing strategy for xanthine assay based on gold nanoclusters and nanozyme

Making the gold-thiolate shell rigid is an appealing and efficient strategy for improving the fluorescence of gold nanoclusters (GNCs). In this study, ultrabright lysozyme-functionalized 5-methyl-2-thiouracil gold nanoclusters ([email protected]) with yellow emission were rationally designed and synthesized based on [email protected] by making the NC shell modified with the lysozyme. The resultant [email protected] exhibited a remarkable luminescence efficiency, high stability, and water-solubility. By combining [email protected] with iron-doped carbon-nanosheet (Fe/C NS) that mimicked peroxidase-like activity, a novel fluorescent nanoprobe was developed for the determination of xanthine. Under the catalysis of xanthine oxidase (XOD), hydrogen peroxide (H2O2) was produced during the oxidation of xanthine. In the presence of H2O2, Fe/C NS can effectively catalyze H2O2 to generate reactive oxygen species (ROS) and subsequently catalyze p-phenylenediamine (PPD) to form its oxidized product (PPDox), thereby quenching the fluorescence of [email protected] at 550 nm via fluorescence resonance energy transfer (FRET). Coupling the peroxidase-like activity of Fe/C NS and XOD cascade reactions, the proposed sensing platform based on [email protected] and Fe/C NS can realize the quantitative analysis of xanthine in the range from 0.5 to 400 µmol L−1, affording a low detection limit of 0.23 µmol L−1. In addition, this study provided satisfactory results for monitoring the xanthine content of real samples.