Direct generation of Ag nanoclusters on reduced graphene oxide nanosheets for efficient catalysis, antibacteria and photothermal anticancer applications

FeS2-modified MXene nanocomposite platform for efficient PTT/CDT/TDT integration through enhanced GSH consumption

Hypoxic microenvironment and glutathione (GSH) accumulation in tumours limit the efficacy of cytotoxic reactive oxygen species (ROS) anti-tumour therapy. To address this challenge, we increased the consumption of GSH and the production of ROS through a novel nanoplatform with the action of inorganic nanoenzymes. In this study, we prepared mesoporous FeS2 using a simple template method, efficiently loaded AIPH, and assembled Ti3C2/FeS2-AIPH@BSA (TFAB) nanocomposites through self-assembly with BSA and 2D Ti3C2. The constructed TFAB nanotherapeutic platform enhanced chemodynamic therapy (CDT) by generating toxic hydroxyl radicals (˙OH) via FeS2, while consuming GSH to reduce the loss of generated ˙OH via glutathione oxidase-like (GSH-OXD). In addition, TFAB is able to stimulate the decomposition of AIPH under 808 nm laser irradiation to produce oxygen-independent biotoxic alkyl radicals (˙R) for thermodynamic therapy (TDT). In conclusion, TFAB represents an innovative nanoplatform that effectively addresses the limitations of free radical-based treatment strategies. Through the synergistic therapeutic strategy of photothermal therapy (PTT), CDT, and TDT within the tumor microenvironment, TFAB nanoplatforms achieve controlled AIPH release, ROS generation, intracellular GSH consumption, and precise temperature elevation, resulting in enhanced intracellular oxidative stress, significant apoptotic cell death, and notable tumor growth inhibition. This comprehensive treatment strategy shows great promise in the field of tumor therapy.

Multifunctional Antimonene-Silver Nanocomposites for Ultra-Multi-Mode and Multi-Analyte Sensing, Parallel and Batch Logic Computing, Long-Text Information Protection

To simulate life's emergent functions, mining the multiple sensing capabilities of nanosystems, and digitizing networks of transduction signals and molecular interactions, is an ongoing endeavor. Here, multifunctional antimonene-silver nanocomposites (AM-Ag NCs) are synthesized facilely and fused for molecular sensing and digitization applications (including ultra-multi-mode and multi-analyte sensing, parallel and batch logic computing, long-text information protection). By mixing surfactant, AM, Ag+ and Sodium borohydride (NaBH4) at room temperature for 5 min, the resulting NCs are comprised of Ag nanoparticles scattered within AM nanosheets and protected by the surfactant. Interestingly, AM-Ag NCs exhibit ultra-multi-mode sensing ability for multiplex metal ions (Hg2+, Fe3+, or Al3+), which significantly improved selectivity (≈2 times) and sensitivity (≈400 times) when analyzing the combined channels. Moreover, multiple sensing capabilities of AM-Ag NCs enable diverse batch and parallel molecular logic computations (including advanced cascaded logic circuits). Ultra-multi-mode selective patterns of AM-Ag NCs to 18 kinds of metal ions can be converted into a series of binary strings by setting the thresholds, and realized high-density, long-text information protection for the first time. This study provides new ideas and paradigms for the preparation and multi-purpose application of 2D nanocomposites, but also offers new directions for the fusion of molecular sensing and informatization.

Advanced Functionalized Nanoclusters (Cu, Ag, and Au) as Effective Catalyst for Organic Transformation Reactions

A considerable amount of research has been carried out in recent years on synthesizing metal nanoclusters (NCs), which have wide applications in the field of optical materials with non-linear properties, bio-sensing, and catalysis. Aside from being structurally accurate, the atomically precise NCs possess well-defined compositions due to significant tailoring, both at the surface and the core, for certain functionalities. To illustrate the importance of atomically precise metal NCs for catalytic processes, this review emphasizes 1) the recent work on Cu, Ag, and Au NCs with their synthesis, 2) the parameters affecting the activity and selectivity of NCs catalysis, and 3) the discussion on the catalytic potential of these metal NCs. Additionally, metal NCs will facilitate the design of extremely active and selective catalysts for significant reactions by elucidating catalytic mechanisms at the atomic and molecular levels. Future advancements in the science of catalysis are expected to come from the potential to design NCs catalysts at the atomic level.

Photothermal/Photoacoustic Therapy Combined with Metal-Based Nanomaterials for the Treatment of Microbial Infections

The increased spread and persistence of bacterial drug-resistant phenotypes remains a public health concern and has contributed significantly to the challenge of combating antibiotic resistance. Nanotechnology is considered an encouraging strategy in the fight against antibiotic-resistant bacterial infections; this new strategy should improve therapeutic efficacy and minimize side effects. Evidence has shown that various nanomaterials with antibacterial performance, such as metal-based nanoparticles (i.e., silver, gold, copper, and zinc oxide) have intrinsic antibacterial properties. These antibacterial agents, such as those made of metal oxides, carbon nanomaterials, and polymers, have been used not only to improve antibacterial efficacy but also to reduce bacterial drug resistance due to their interaction with bacteria and their photophysical properties. These nanostructures have been used as effective agents for photothermal therapy (PTT) and photodynamic therapy (PDT) to kill bacteria locally by heating or the controlled production of reactive oxygen species. Additionally, PTT or PDT therapies have also been combined with photoacoustic (PA) imaging to simultaneously improve treatment efficacy, safety, and accuracy. In this present review, we present, on the one hand, a summary of research highlighting the use of PTT-sensitive metallic nanomaterials for the treatment of bacterial and fungal infections, and, on the other hand, an overview of studies showing the PA-mediated theranostic functionality of metal-based nanomaterials.

BNN/TiO2 nanocomposite system-modified dental flow resins and the mechanism of the enhancement of mechanical and antibacterial properties

Robust and antibacterial dental resins are essential for repairing the shape and function of the teeth. However, an ingenious way to achieve a synergistic enhancement of these two properties is still lacking. In this work, guided by molecular dynamics (MD) calculations, a boron nitride nanosheet (BNN)/titanium dioxide (TiO2) nanocomposite system was synthesized and used to modify the dental flow resin to enhance its mechanical and antimicrobial properties. The mechanical and antimicrobial enhancement mechanisms were further explored. The modified resin demonstrated outstanding performance improvement with 88.23%, 58.47%, 82.01%, and 55.06% improvement in compressive strength (CS), microhardness (MH), flexural strength (FS), and elastic modulus (EM), respectively. Moreover, the modified resin could effectively inhibit the growth of Streptococcus mutans (S. mutans) regardless of aging in water and the inhibition rates were more than 90%. In conclusion, the modified resin is expected to be an ideal restorative material for clinical applications.

A bimetallic Ag15Cu12(S-c-C6H11)18(CH3COO)3 nanocluster featuring an irregular Ag12 kernel

Here, we report the synthesis and atomic structure of a Ag₁₅Cu₁₂(SR)₁₈(CH₃COO)₃·(C₆H₁₄) nanocluster (Ag₁₅Cu₁₂ for short, SR denotes cyclohexanethiol), confirmed by single-crystal X-ray diffraction (SC-XRD), electrospray ionization mass spectrometry (ESI-MS), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). X-ray crystallographic analysis revealed that Ag₁₅Cu₁₂ consisted of an irregular Ag₁₂ core, stabilized by the Ag₃Cu₁₂(SR)₁₈(CH₃COO)₃ shell. The shell consisted of two nearly planar Cu₃(SR)₆ moieties, three monomeric [-SR-Ag-SR-] units and three Cu₂(CH₃COO) staples. Furthermore, time-dependent density functional theory (TD-DFT) simulation was performed to interpret the optical absorption features of Ag₁₅Cu₁₂. Overall, this work will broaden and deepen the understanding of Ag-Cu alloy nanoclusters.

Three-Dimensional Reduced Graphene Oxide Hybrid Nano-Silver Scaffolds with High Antibacterial Properties

In recent years, hazardous wastewater treatment has been a complex and global problem. In this work, by considering the antimicrobial activity of Ag nanoparticles (AgNPs) and reduced graphene oxide (rGO), we constructed an antibacterial device (G-AgNP) with AgNPs conformably deposited onto a 3D scaffold of reduced graphene oxide in situ. The major limitation, which is difficult to recycle, of two-dimensional graphene-silver composite materials in previous studies is improved. Characterization techniques, SEM, TEM, XRD, and XPS, confirmed the synthesis of nanocomposites. Attributed to its larger specific area, more active sites, and synergistic enhancement, the G-AgNP device demonstrated the best bacterial removal capacity, with an antibacterial rate for both E. coli and S. aureus as high as 100% at quite low AgNP contents. The reported G-AgNP has potential application as a wearable sewage treatment device and for the protection of wearable sensors as a promising sterilizing candidate based on its high and stable antibacterial efficiency.

Integrating Dual-Interfacial Liquid Metal Based Nanodroplet Architectures and Micro-Nanostructured Engineering for High Efficiency Solar Energy Harvesting

Broadband strong absorption of solar light over a wide range of angles, low heat loss, and excellent structural reliability are of significance for enhancing solar harvesting of photothermal materials; however, it remains a challenge to achieve these attributes simultaneously. Herein, a tailored photothermal composite nanodroplet (LMP-rGO) featured with dual-interface, which comprises liquid metal (LM) core with polydopamine (PDA) photothermal middle layer of tunable thickness and reduced graphene oxide (rGO) shell, is particularly prepared. Thermal-insulating PDA coating and light-absorbing carbonaceous shell allow it to synergistically suppress heat loss and reinforce photon absorptivity. To maximize photothermal conversion and photon harvesting yield on solar light, inspired by light trapping architecture, a three-dimensional (3D) stepped micropyramid grating array framework is tactfully designed to ameliorate light coupling. Utilizing the scalability and cost-effectiveness of the poly(vinyl alcohol) (PVA), the flexible 3D-structured PVA/LMP-rGO absorbers are successfully constructed via a controllable casting molding strategy. As a proof-of-concept, the developed micrograting absorber exhibits a desirable combination of strong broadband selective light absorption (94.9% for parallel to the grating direction and 97.3% for perpendicular to the grating direction), superior photothermal conversion effect (89.4%), high heat flux density, and fascinating mechanical properties. Also, an efficient and steady solar-driven thermoelectric generator (STEG) system for real-time solar-heat-electric conversion, with its high peak power density of 245.9 μW cm^-2 under one sun irradiation, is further displayed, making an important step to rationally design LM-based nanocomposite droplets for solar energy harvesting.

Green synthesis of Ag nanoparticles using elm pod polysaccharide for catalysis and bacteriostasis

The green synthesis of silver nanoparticles (Ag NPs) for catalysis and biological applications has gained great interest. Natural elm pods are a type of food that possesses anti-inflammatory and pain-relieving effects. In this study, elm pod polysaccharide (EPP) was extracted from elm pods using hot water extraction for the first time. Biocompatible EPP-stabilized silver nanoparticles (EPP-Ag_n NPs) were prepared by using a green synthesis method. The EPP-Ag₂₅ NPs had a hydrodynamic size of 40.9 nm and a highly negative surface charge of -27.4 mV. Furthermore, EPP-Ag₂₅ NPs exhibited high catalytic activity for the reduction of 4-nitrophenol, and the catalytic reaction followed a pseudo-first order kinetic equation. More importantly, the inhibition rate of EPP-Ag₂₅ NPs on Escherichia coli was 71 % when samples were treated with an 808 nm laser. Besides, EPP-Ag_n NPs effectively inhibited the proliferation of tumor cells irradiated by an 808 nm laser. The improved performance of EPP-Ag_n NPs was due to the good stability of EPP. Taken together, EPP-Ag_n NPs had good stability, catalytic activity, antibacterial and antitumor ability under laser irradiation. EPP is a good stabilizer for many nanoparticles which have broad applications in the field of catalysis and biomedicine in the future.

Antibacterial metal nanoclusters

Combating bacterial infections is one of the most important applications of nanomedicine. In the past two decades, significant efforts have been committed to tune physicochemical properties of nanomaterials for the development of various novel nanoantibiotics. Among which, metal nanoclusters (NCs) with well-defined ultrasmall size and adjustable surface chemistry are emerging as the next-generation high performance nanoantibiotics. Metal NCs can penetrate bacterial cell envelope more easily than conventional nanomaterials due to their ultrasmall size. Meanwhile, the abundant active sites of the metal NCs help to catalyze the bacterial intracellular biochemical processes, resulting in enhanced antibacterial properties. In this review, we discuss the recent developments in metal NCs as a new generation of antimicrobial agents. Based on a brief introduction to the characteristics of metal NCs, we highlight the general working mechanisms by which metal NCs combating the bacterial infections. We also emphasize central roles of core size, element composition, oxidation state, and surface chemistry of metal NCs in their antimicrobial efficacy. Finally, we present a perspective on the remaining challenges and future developments of metal NCs for antibacterial therapeutics.

Nanocluster-Based Drug Delivery and Theranostic Systems: Towards Cancer Therapy

Over the last decades, the global life expectancy of the population has increased, and so, consequently, has the risk of cancer development. Despite the improvement in cancer therapies (e.g., drug delivery systems (DDS) and theranostics), in many cases recurrence continues to be a challenging issue. In this matter, the development of nanotechnology has led to an array of possibilities for cancer treatment. One of the most promising therapies focuses on the assembly of hierarchical structures in the form of nanoclusters, as this approach involves preparing individual building blocks while avoiding handling toxic chemicals in the presence of biomolecules. This review aims at presenting an overview of the major advances made in developing nanoclusters based on polymeric nanoparticles (PNPs) and/or inorganic NPs. The preparation methods and the features of the NPs used in the construction of the nanoclusters were described. Afterwards, the design, fabrication and properties of the two main classes of nanoclusters, namely noble-metal nanoclusters and hybrid (i.e., hetero) nanoclusters and their mode of action in cancer therapy, were summarized.

Facile one pot microbe-mediatedin situsynthesis and antibacterial activity of reduced graphene oxide-silver nanocomposite

The present research deals with the development of a novel bioinspiredin situfabrication of reduced graphene oxide (rGO)-silver nanoparticle (AgNPs) nanocomposite (rGO@AgNCs) using microbes namelyPseudomonas aeruginosa(PA) andStaphylococcus aureus(SA). The fabricated rGO@AgNCs were characterized using Ultraviolet-visible (UV-Vis) spectroscopy, Fourier-transform infrared spectroscopy (FTIR), particle size analysis, polydispersity index (PDI), zeta potential analysis, energy dispersive x-ray analysis (EDAX), Raman spectroscopy, powder x-ray diffraction (PXRD), high-resolution transmission electron microscopy (HR-TEM) analysis, etc. Furthermore, the rGO@AgNCs-PA and rGO@AgNCs-SA interaction with serum protein, pH stability study, andin vitrodissolution of AgNPs were also performed. The research findings of the proposed study demonstrated the simultaneous reduction of graphene oxide (GO) and AgNPs and the formation of rGO@AgNCs in the presence of microbes. Thein vitrodissolution studies of rGO@AgNCs composites showed better AgNPs dissolution with controlled release and offered remarkable matrix integrity throughout the dissolution period. The size and stability of rGO@AgNCs-PA and rGO@AgNCs-SA had no significant changes at physiological pH 7.4. A minimal decrease in the zeta potential of rGO@AgNCs was observed, which may be due to the weak interaction of nanocomposites and albumin. The antibacterial application of the synthesized nanocomposite was evaluated against a pathogenic mastitis-forming bacterium. The obtained results suggested an admirable antibacterial activity of synthesized nanocomposites against the tested microbes. This knowledge will assist the scientific fraternity in designing novel antibacterial agents with enhanced antibacterial activity against various veterinary pathogens in near future.

Plasmonic nano-antimicrobials: properties, mechanisms and applications in microbe inactivation and sensing

Bacterial, viral and fungal infections pose serious threats to human health and well-being. The continuous emergence of acute infectious diseases caused by pathogenic microbes and the rapid development of resistances against conventional antimicrobial drugs necessitates the development of new and effective strategies for the safe elimination of microbes in water, food or on surfaces, as well as for the inactivation of pathogenic microbes in human hosts. The need for new antimicrobials has triggered the development of plasmonic nano-antimicrobials that facilitate both light-dependent and -independent microbe inactivation mechanisms. This review introduces the relevant photophysical mechanisms underlying these plasmonic nano-antimicrobials, and provides an overview of how the photoresponses and materials properties of plasmonic nanostructures can be applied in microbial pathogen inactivation and sensing applications. Through a systematic analysis of the inactivation efficacies of different plasmonic nanostructures, this review outlines the current state-of-the-art in plasmonic nano-antimicrobials and defines the application space for different microbial inactivation strategies. The advantageous optical properties of plasmonic nano-antimicrobials also enhance microbial detection and sensing modalities and thus help to avoid exposure to microbial pathogens. Sensitive and fast plasmonic microbial sensing modalities and their theranostic and targeted therapeutic applications are discussed.

Covalent anchoring of atomically precise glutathione-protected gold nanoclusters on graphene oxide nanosheets

This paper describes the development of a novel method of producing nanocomposites consisting of gold nanoclusters anchored on graphene oxide nanosheets in a cost-effective and reproducible manner. The novelty of the technique hinges on the covalent functionalization of atomically precise subnanometer gold clusters protected by glutathione (Au15SG13 and Au25SG18) on to graphene oxide (GO) nanosheets according to the 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride crosslinking method, using the existing carboxylic groups present both at the surfaces of the nanoclusters and the GO nanosheets. The atomic precision of glutathione-protected gold nanoclusters was evidenced by electrospray ionization mass spectrometry. The formed hybrid nanocomposites were characterized by TEM measurements and exhibit nonlinear optical properties characteristic of GO, in particular a strong second harmonic scattering response as well as a multi-photon excited fluorescence spectrum characterized by a broad band in the visible range between 350 and 700 nm. Atomically precise nanoclusters covalently linked to GO nanosheets are therefore promising for new applications in the areas of optoelectronics and photovoltaics.

Hybrids of Upconversion Nanoparticles and Silver Nanoclusters Ensure Superior Bactericidal Capability via Combined Sterilization

It is highly desired to develop new antibacterial agents with superior bactericidal efficiency for minimizing the damage to biological cells. We developed a combined antibacterial nanohybrid exhibiting a superb bactericidal effect and excellent biocompatibility by integrating upconversion nanoparticles (UCNPs) with silver nanoclusters (AgNCs). UCNPs and methylene blue (MB) molecules were encapsulated with silica microspheres via microemulsion, with MB as the photosensitizer. Silver ions (Ag⁺) were reduced by amino groups on the surface of silica spheres, wherein silver nanoclusters (AgNCs) were formed in situ to produce the nanohybrid, UCNPs@SiO₂(MB)@AgNCs. UCNPs emit visible light at 655 nm under excitation by near-infrared radiation (NIR, 980 nm). MB absorbs the emission from UCNPs to generate toxic singlet oxygen (¹O₂), which leads to the apoptosis of bacteria cells. Meanwhile, silver ions released from AgNCs destroy the bacteria membrane structure. Upon NIR irradiation at 980 nm for 10 min, 8.33 μg mL^-1 nanohybrid results in a 100% killing rate for both Gram-positive S. aureus (+) and Gram-negative E. coli (-).