Atomically precise water-soluble gold nanoclusters (Au NCs) protected by organic ligands have attracted growing attention in serving as unique nanomaterials with the potential to generate theranostic tools (bioimaging, biosensing, and biotherapy), due to their ultrasmall size, superior photoluminescence, good biocompatibility, and nontoxicity. More importantly, Au NCs afford a well-defined atomic packing structure and molecular purity, providing a superior platform to unravel the structure–performance correlations for biodistribution, biological pharmacokinetics, and excretion of Au NCs. In this Review, we mainly survey the synthesis of water-soluble Au NCs and the recent progress in biomedicine of Au NCs, including bioimaging, biosensing, and biotherapy. The effects of ligand and size on the biomedical properties are discussed in detail. We hope that the advances in this research area can expand the applications of Au NCs in biomedicine.

5-Hydroxymethylfurfural (HMF) serves as an important bridge connecting biomass resources with fossil fuels. Its downstream product, 2,5-furandicarboxylic acid (FDCA), is a renewable alternative to terephthalic acid (TPA) in the synthesis of various polymer materials. In this study, we successfully synthesized four ruthenium-based catalysts with varying valence states supported on carbon nanotubes (CNTs) and compared the performance of HMF electrooxidation. Among these, the Ru^+2.9 catalyst demonstrated the highest activity for the electrochemical oxidation of HMF to FDCA in the neutral medium (0.1 M K₂SO₄). Notably, the FDCA yield reached 90.2% under an applied potential of 0.95 V (vs. Ag/AgCl) after 24 h. Mechanistic analysis revealed that the superior specific capacitance of the Ru^+2.9 catalyst significantly facilitated the reaction process. This work represents a more cost-effective approach to avoid the need for excessive alkaline additives during catalyst preparation and the HMF oxidation process, and FDCA separated easily after cooling the reaction solution down.