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 (MT-LZ@GNCs) with yellow emission were rationally designed and synthesized based on MT@GNCs by making the NC shell modified with the lysozyme. The resultant MT-LZ@GNCs exhibited a remarkable luminescence efficiency, high stability, and water-solubility. By combining MT-LZ@GNCs 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 MT-LZ@GNCs 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 MT-LZ@GNCs and Fe/C NS can realize the quantitative analysis of xanthine in the range from 0.5 to 400 mu mot L-1, affording a low detection limit of 0.23 mu mol L-1. In addition, this study provided satisfactory results for monitoring the xanthine content of real samples.

Automated summary

Rigidifying the gold-thiolate shell is an effective strategy to enhance the fluorescence of gold nanoclusters (GNCs). In this study, ultrabright lysozyme-functionalized 5-methyl-2-thiouracil gold nanoclusters (MT-LZ@GNCs) were synthesized and exhibited remarkable luminescent properties. By combining MT-LZ@GNCs with iron-doped carbon-nanosheet (Fe/C NS) mimicking peroxidase-like activity, a novel fluorescent nanoprobe was developed for the quantitative analysis of xanthine. The proposed sensing platform showed a wide detection range and a low detection limit, with potential applications in real sample monitoring.