The development of novel strategies for the synthesis of water-soluble alloy nanoclusters (NCs) and investigations of their alloying mechanisms are highly desirable. Herein, we report the design of a metal ion-induced alloying strategy for the synthesis of atomically precise water-soluble alloy NCs. The transformation of Au₁₅(GSH)₁₃ NCs as model seeds (here GSH denotes water-soluble glutathione) into Au_18−xAg_x(GSH)₁₄ NCs was triggered using Ag(I) ions; subsequently, Au(III) ions were employed to convert the variable-composition Au_18−xAg_x(GSH)₁₄ NCs into fixed-composition alloy Au₂₆Ag(GSH)₁₇Cl₂ NCs. Monitoring of the alloying process showed that the formation of Au_18−xAg_x(GSH)₁₄ NCs proceeds through the two electron-hopping events (2e⁻ Au₁₅ → 2e⁻ (AuAg)_15–17 → 4e⁻ (AuAg)_18–19 → 4e⁻ (AuAg)₁₈), whereas the transformation of (AuAg)₁₈ into Au₂₆Ag mainly involved the formation of intermediate species Au₂₆(GSH)₁₇Cl_n (n = 0–2). Moreover, we determined that the single Ag atom in Au₂₆Ag NCs resides on the NC surface. This study not only provides a novel strategy for the synthesis of water-soluble alloy NCs but also contributes to the fundamental understanding of the alloying mechanism of metal NCs.

Cu(I)-catalyzed azide-alkyne cycloadditions (CuAAC) have gained increasing interest in the selective labeling of living cells and organisms with biomolecules. However, their application is constrained either by the high cytotoxicity of Cu(I) ions or the low activity of CuAAC in the internal space of living cells. This paper reports the design of a novel Cu-based nanocatalyst, water-soluble thiolated Cu₃₀ nanoclusters (NCs), for living cell labeling via CuAAC. The Cu₃₀ NCs offer good biocompatibility, excellent stability, and scalable synthesis (e.g., gram scale), which would facilitate potential commercial applications. By combining the highly localized Cu(I) active species on the NC surface and good structural stability, the Cu₃₀ NCs exhibit superior catalytic activities for a series of Huisgen cycloaddition reactions with good recyclability. More importantly, the biocompatibility of the Cu₃₀ NCs enables them to be a good catalyst for CuAAC, whereby the challenging labeling of living cells can be achieved via CuAAC on the cell membrane. This study sheds light on the facile synthesis of atomically precise Cu NCs, as well as the design of novel Cu NCs-based nanocatalysts for CuAAC in intracellular bioorthogonal applications.

Ultrasmall silver nanoclusters (Ag NCs) with rich surface chemistry and good biocompatibility are promising in antibacterial application, however, further development of Ag NCs for practical settings has been constrained by their relatively weak antibacterial activity. Using the nutritionally-rich medium for bacteria (e.g., Luria-Bertani (LB) medium) to coat active Ag NCs could further improve their antibacterial activity. Here, we provide a delicate design of a highly efficient Ag NCs@ELB antibacterial agent (ELB denotes the extract of LB medium) by anchoring Ag NCs inside the ELB species via light irradiation. The as-designed Ag NCs with bacterium-favored nutrients on the surface can be easily swallowed by the bacteria, boosting the production of the intracellular reactive oxygen species (ROS, about 2-fold of that in the pristine Ag NCs). Subsequently, a higher concentration of ROS generated in Ag NCs@ELB leads to enhanced antibacterial activity, and enables to reduce the colony forming units (CFU) of both gram-positive and gram-negative bacteria with 3-4 orders of magnitude less than that treated with the pristine Ag NCs. In addition, the Ag NCs@ELB also shows good biocompatibility. This study suggests that surface engineering of active species (e.g., Ag NCs) with nutritionally-rich medium of the bacteria is an efficient way to improve their antibacterial activity.