Thiolate-protected atomically precise nanoclusters (NCs) demonstrate a series of unique luminescent characteristics attributed to their various peculiar electronic structures. Therefore, fluorescent NCs present extraordinary practical values in biosensing and bioimaging research fields. Nevertheless, restricted by the types of fluorescent NCs, there are great difficulties in promoting the development of NCs in fluorescent research areas. As a result, it is of significant necessity for researchers to develop new synthetic pathways to produce high-quality fluorescent NCs. According to the analysis about the structural characteristics of fluorescent NCs, some general features like longer motif and higher ligand-to-metal ratio can be found, consistent to some presented regularities in etching reaction. Consequently, in this work, we used Au₂₅(MHA)₁₈ (MHA = 6-mercaptohexanoic acid) as a model nanocluster and utilized the etching reaction to systematically explore etching products and their corresponding luminescent properties. Moreover, we also identified three main reaction processes in the entire etching reaction process, which can generate new metal nanocluster species with various fluorescent properties. Hence, the etching reaction will provide a good platform to produce new luminescent metal NC species.

Rapid and accurate chemical composition identification is critically important in chemistry. While it can be achieved with optical absorption spectrometry by comparing the experimental spectra with the reference data when the chemical compositions are simple, such application is limited in more complicated scenarios especially in nano-scale research. This is due to the difficulties in identifying optical absorption peaks (i.e., from “featureless” spectra) arose from the complexity. In this work, using the ultraviolet–visible (UV–Vis) absorption spectra of metal nanoclusters (NCs) as a demonstration, we develop a machine-learning-based method to unravel the compositions of metal NCs behind the “featureless” spectra. By implementing a one-dimensional convolutional neural network, good matches between prediction results and experimental results and low mean absolute error values are achieved on these optical absorption spectra that human cannot interpret. This work opens a door for the identification of nanomaterials at molecular precision from their optical properties, paving the way to rapid and high-throughput characterizations.

Understanding the interaction of nanomaterials with biological systems has always been of high concern and interest. An emerging type of nanomaterials, ultrasmall metal nanoclusters (NCs, < 2 nm in size), are promising in this aspect due to their well-defined molecular formulae and structures, as well as unique physical and chemical properties that are distinctly different from their larger counterparts (metal nanoparticles). For example, metal NCs possess intrinsic strong luminescence, which can be used for real-time tracking of their interactions with biological systems. Herein, luminescent gold (Au) NCs were used as traceable antimicrobial agents to study their interactions with the bacteria and to further understand their underlining antimicrobial mechanism. It is shown for the first time that the Au NCs would first attach on the bacterial membrane, penetrate, and subsequently accumulate inside the bacteria. Thereafter, the internalized Au NCs would induce reactive oxygen species (ROS) generation and damage the bacterial membrane, resulting in the leakage of bacterial contents, which can finally kill the bacteria. Traceable Au NCs (or other metal NCs) provide a promising platform to study the antimicrobial mechanisms as well as other fundamentals on the interfacing of functional nanomaterials with the biological systems, further increasing their acceptance in various biomedical 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.

Oxidation of organic pollutants by sulfate radicals produced via activation of persulfate has emerged as a promising advanced oxidation technology to address various challenging environmental issues. The development of an effective, environmentally-friendly, metal-free catalyst is the key to this technology. Additionally, a supported catalyst design is more advantageous than conventional suspended powder catalysts from the point of view of mass transfer and practical engineering applications (e.g. post-use separation). In this study, a metal-free N-doped reduced graphene oxide (N-rGO) catalyst was prepared via a facile hydrothermal method. N-rGO filters were then synthesized by facile vacuum filtration, such that water can flow through nanochannels within the filters. Various advanced characterization techniques were employed to obtain structural and compositional information of the as-synthesized N-rGO filters. An optimized phenol oxidative flux of 0.036 ± 0.002 mmol·h^–1 was obtained by metal-free catalytic activation of persulfate at an influent persulfate concentration of 1.0 mmol·L^–1 and filter weight of 15 mg, while a N-free rGO filter demonstrated negligible phenol oxidation capability under similar conditions. Compared to a conventional batch system, the flow-through design demonstrates obviously enhanced oxidation kinetics (0.036 vs. 0.010 mmol·h^–1), mainly due to the liquid flow through the filter leading to convection-enhanced transfer of the target molecule to the filter active sites. Overall, the results exemplified the advantages of organic compound removal by catalytic activation of persulfate using a metal-free catalyst in flowthrough mode, and demonstrated the potential of N-rGO filters for practical environmental applications.

To achieve better control of the formation of silver sulfide (Ag₂S) nanoparticles, ultrasmall Ag nanoclusters protected by thiolate ligands (Ag₄₄(SR)₃₀ and Ag₁₆(GSH)₉) are used as precursors, which, via delicate chemistry, can be readily converted to monodisperse Ag₂S nanoparticles with controllable sizes (4–16 nm) and switchable solvent affinity (between aqueous and organic solvents). This new synthetic protocol makes use of the atomic monodispersity and rich surface chemistry of Ag nanoclusters and a novel two-phase protocol design, which results in a well-controlled reaction environment for the formation of Ag₂S nanoparticles.

While thiolate-protected Au nanoclusters (NCs) have drawn considerable interest in various fields, their poor stability in aqueous solution remains a major hurdle for practical applications. Here, we report a unique strategy based on ligand-shell engineering to improve the stability of thiolated Au NCs in solution. By employing two thiol-terminated ligands having oppositely charged functional groups on the surface of the NCs, we demonstrate that the electrostatic attraction between the oppositely charged functional groups of neighboring ligands could amplify the coordination among surface ligands, leading to the formation of pseudo-cage-like structures on the NC surface that could offer higher protection to the Au core in aqueous solution. The strategy developed in this study could be extended to other metal NCs, further paving the way toward practical applications.

This paper reports a simple yet efficient method for the synthesis of hierarchical TiO₂-B nanowire@α-Fe₂O₃ nanothorn core-branch arrays based on a stepwise hydrothermal approach. The as-fabricated hybrid arrays show impressive performance as a high-capacity anode for lithium-ion batteries. The key design in this study is a core-branch hybrid architecture, which not only provides large surface active sites for lithium ion insertion/extraction, but also enables fast charge transport owing to the reduced diffusion paths for both electrons and lithium ions. The peculiar combination of attributes of TiO₂ (good structural stability) and Fe₂O₃ (large specific capacity) provides the hybrid array electrodes with several desirable electrochemical features: large reversible capacity (~800 mA·h·g^–1 for specific mass capacity and ~750 μA·h·cm^–2 for specific areal capacity), good cycling stability, and high rate capability. The impressive electrochemical performance, together with the facile synthesis procedure, may provide an efficient platform to integrate the TiO₂ nanowire@Fe₂O₃ nanothorn core-branch arrays as a three-dimensional thin film electrode for lithium-ion microbatteries.

Metallic silver (Ag) and its ability to combat infection have been known since ancient history. In the wake of nanotechnology advancement, silver's efficacy to fight broad spectrum bacterial infections is further improved in the form of Ag nanoparticles (NPs). Recent studies have ascribed the broad spectrum antimicrobial properties of Ag NPs to dissociation of Ag⁺ ions from the NPs, which may not be entirely applicable when the size of Ag NPs decreases to the sub-2 nm range [denoted Ag nanoclusters (NCs)]. In this paper we report that ultrasmall glutathione (GSH)-protected Ag⁺-rich NCs (Ag⁺-R NCs for short, with a predominance of Ag⁺ species in the NCs) have much higher antimicrobial activities towards both gram-negative and gram-positive bacteria than the reference NC, GSH–Ag⁰-R NCs. They have the same size and surface ligand, but with different oxidation states of the core silver. This interesting finding suggests that the undissociated Ag⁺-R NCs armed with abundant Ag⁺ ions on the surface are highly active in bacterial killing, which was not observed in the system of their larger counterpart, Ag NPs.