A fundamental understanding of the luminescence of Au-thiolate nanoclusters (NCs), such as the origin of emission and the size effect in luminescence, is pivotal to the development of efficient synthesis routes for highly luminescent Au NCs. This paper reports an interesting finding of Au(I)-thiolate complexes: strong luminescence emission by the mechanism of aggregation-induced emission (AIE). The AIE property of the complexes was then used to develop a simple one-pot synthesis of highly luminescent Au-thiolate NCs with a quantum yield of ~15%. Our key strategy was to induce the controlled aggregation of Au(I)-thiolate complexes on in situ generated Au(0) cores to form Au(0)@Au(I)-thiolate core-shell NCs where strong luminescence was generated by the AIE of Au(I)-thiolate complexes on the NC surface. We were able to extend the synthetic strategy to other thiolate ligands with added functionalities (in the form of custom-designed peptides). The discovery (e.g., identifying the source of emission and the size effect in luminescence) and the synthesis protocols in this study can contribute significantly to better understanding of these new luminescence probes and the development of new synthetic routes.

For nearly a decade, researchers have debated the mechanisms by which AgNPs exert toxicity to bacteria and other organisms. The most elusive question has been whether the AgNPs exert direct "particle-specific" effects beyond the known antimicrobial activity of released silver ions (Ag(+)). Here, we infer that Ag(+) is the definitive molecular toxicant. We rule out direct particle-specific biological effects by showing the lack of toxicity of AgNPs when synthesized and tested under strictly anaerobic conditions that preclude Ag(0) oxidation and Ag(+) release. Furthermore, we demonstrate that the toxicity of various AgNPs (PEG- or PVP- coated, of three different sizes each) accurately follows the dose-response pattern of E. coli exposed to Ag(+) (added as AgNO(3)). Surprisingly, E. coli survival was stimulated by relatively low (sublethal) concentration of all tested AgNPs and AgNO(3) (at 3-8 μg/L Ag(+), or 12-31% of the minimum lethal concentration (MLC)), suggesting a hormetic response that would be counterproductive to antimicrobial applications. Overall, this work suggests that AgNP morphological properties known to affect antimicrobial activity are indirect effectors that primarily influence Ag(+) release. Accordingly, antibacterial activity could be controlled (and environmental impacts could be mitigated) by modulating Ag(+) release, possibly through manipulation of oxygen availability, particle size, shape, and/or type of coating.

This paper reports a simple, one-pot, template-free synthesis of flower-like Au nanoparticles (three-dimensional branched nanoparticles with more than 10 tips) with high yield and good size monodispersity at room temperature. The size of the Au nanoflowers could be tuned by controlling the composition of the starting reaction mixture. The key synthesis strategy was to use a common Good's buffer, HEPES, as a weak reducing and particle stabilizing agent to confine the growth of the Au nanocrystals in the special reaction region of limited ligand protection (LLP). Time-course measurements by UV-vis spectroscopy and TEM were used to follow the reaction progress and the evolution of the flower-like shape. The Au nanoflowers exhibited strong surface-enhanced effects which were utilized in the design of an efficient, stable, and nontoxic Raman-active tag for in vivo applications.

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This paper reports a simple and scalable method for the synthesis of highly fluorescent Ag, Au, Pt, and Cu nanoclusters (NCs) based on a mild etching environment made possible by phase transfer via electrostatic interactions. Using Ag as a model metal, a simple and fast (total synthesis time < 3 h) phase transfer cycle (aqueous → organic (2 h incubation) → aqueous) has been developed to process originally polydisperse, nonfluorescent, and unstable Ag NCs into monodisperse, highly fluorescent, and extremely stable Ag NCs in the same phase (aqueous) and protected by the same thiol ligand. The synthetic protocol was successfully extended to fabricate highly fluorescent Ag NCs protected by custom-designed peptides with desired functionalities (e.g., carboxyl, hydroxyl, and amine). The facile synthetic method developed in this study should largely contribute to the practical applications of this new class of fluorescence probes.