Engineering Ultrasmall Metal Nanoclusters as Promising Theranostic Agents

Levonorgestrel protected Au10 cluster for hypochlorite sensing in living organisms

BACKGROUND

Highly reactive oxygen species (ROS) could lead to serious damage in living cells and are associated with many diseases like cancers. Metal cluster with strong fluorescence has great potential in biosensing and many thiolate ligands-protected clusters have been applied in ROS sensing.

RESULTS

In this work, we synthesized levonorgestrel protected Au10 cluster with specific sensing ability for highly ROS via crystal transformation from Au8 cluster, demonstrating the significance of inner core structure on detecting performance. The detection limit of Au10 cluster for ClO- could reach as low as 0.1 μM. This fluorescent probe not only achieving detection of exogenous ClO- in living cells and zebrafish, but also successful imaging of endogenous ClO- in HeLa and HepG2 cells.

SIGNIFICANCE

In comparison to previously reported cluster-based sensors for ROS, this work proposes a different reaction mechanism of metal nanoclusters for ROS detection (breakage of gold-alkynyl bond and oxidation of alkynyl group). This provides new directions for designing specific ROS probes and broadens the applications of metal clusters in disease diagnostics.

Fluorescent metal nanoclusters: From luminescence mechanism to applications in enzyme activity assays

Metal nanoclusters (MNCs) have outstanding fluorescence property and biocompatibility, which show widespread applications in biological analysis. Particularly, evaluation of enzyme activity with the fluorescent MNCs has been developed rapidly within the past several years. In this review, we first introduced the fluorescent mechanism of mono- and bi-metallic nanoclusters, respectively, whose interesting luminescence properties are mainly resulted from electron transfer between the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels. Meanwhile, the charge migration within the structure occurs through ligand-metal charge transfer (LMCT) or ligand-metal-metal charge transfer (LMMCT). On such foundation, diverse enzyme activities were rigorously evaluated, including three transferases and nine hydrolases, in turn harvesting rapid research progresses within past 5 years. Finally, we summarized the design strategies for evaluating enzyme activity with the MNCs, presented the major issues and challenges remained in the relevant research, coupled by showing some improvement measures. This review will attract researchers dedicated to the studies of the MNCs and provide some constructive insights for their further applications in enzyme analysis.

Antibiotic Alternatives: Multifunctional Ultra-Small Metal Nanoclusters for Bacterial Infectious Therapy Application

The prevalence of major bacterial infections has emerged as a significant menace to human health and life. Conventional treatment methods primarily rely on antibiotic therapy, but the overuse of these drugs has led to a decline in their efficacy. Moreover, bacteria have developed resistance towards antibiotics, giving rise to the emergence of superbugs. Consequently, there is an urgent need for novel antibacterial agents or alternative strategies to combat bacterial infections. Nanoantibiotics encompass a class of nano-antibacterial materials that possess inherent antimicrobial activity or can serve as carriers to enhance drug delivery efficiency and safety. In recent years, metal nanoclusters (M NCs) have gained prominence in the field of nanoantibiotics due to their ultra-small size (less than 3 nm) and distinctive electronic and optical properties, as well as their biosafety features. In this review, we discuss the recent progress of M NCs as a new generation of antibacterial agents. First, the main synthesis methods and characteristics of M NCs are presented. Then, we focus on reviewing various strategies for detecting and treating pathogenic bacterial infections using M NCs, summarizing the antibacterial effects of these nanoantibiotics on wound infections, biofilms, and oral infections. Finally, we propose a perspective on the remaining challenges and future developments of M NCs for bacterial infectious therapy.

Possibilities and limitations of solution-state NMR spectroscopy to analyze the ligand shell of ultrasmall metal nanoparticles

Ultrasmall nanoparticles have a diameter between 1 and 3 nm at the border between nanoparticles and large molecules. Usually, their core consists of a metal, and the shell of a capping ligand with sulfur or phosphorus as binding atoms. While the core structure can be probed by electron microscopy, electron and powder diffraction, and single-crystal structure analysis for atom-sharp clusters, it is more difficult to analyze the ligand shell. In contrast to larger nanoparticles, ultrasmall nanoparticles cause only a moderate distortion of the NMR signal, making NMR spectroscopy a qualitative as well as a quantitative probe to assess the nature of the ligand shell. The application of isotope-labelled ligands and of two-dimensional NMR techniques can give deeper insight into ligand-nanoparticle interactions. Applications of one- and two-dimensional NMR spectroscopy to analyze ultrasmall nanoparticles are presented with suitable examples, including a critical discussion of the limitations of NMR spectroscopy on nanoparticles.

A hydrogel-functionalized silver nanocluster for bacterial-infected wound healing

The ever-growing challenges of traditional antibiotic therapy and chronic wound healing have created a hot topic for the development and application of new antimicrobial agents. Silver nanoclusters (Ag NCs) with ultrasmall sizes (<2 nm) and antibacterial effects are promising candidates for next-generation antibiotics, particularly against multi-drug resistant strains. However, the biosafety in the clinical application of Ag NCs remains suboptimal despite some existing studies of Ag NCs for biomedical applications. Considering this, an ultrasmall Ag NC with excellent water solubility was synthesized by a two-phase ligand-exchange method, which exhibits broad-spectrum antibacterial performance. The minimum inhibitory concentrations of Ag NCs against MRSA, S. aureus, P. aeruginosa and E. coli were evaluated as 50, 80, 5 and 5 μg mL-1, respectively. Furthermore, a carbomer hydrogel was prepared to be incorporated into the Ag NCs for achieving excellent biocompatibility and biosafety. In vitro experiments demonstrate that the Ag NC-gel exhibits good antibacterial properties with lower cytotoxicity. Finally, in vivo experiments suggest that this ultrasmall Ag NC functionalized with the hydrogel can serve as an effective and safe antimicrobial agent to aid in wound healing.

Synergetic-effect-enhanced electrochemiluminescence of zein-protected Au-Ag bimetallic nanoclusters for CA15-3 detection

In this work, a sandwich-type electrochemiluminescence (ECL) system was constructed for the detection of CA15-3. Gold-silver bimetallic nanoclusters (Au-Ag BNCs) with zein as a protective ligand were synthesized, and the excellent ECL performance of this material was demonstrated for the first time. Zein carrying a variety of groups that ligated with Au-Ag BNCs, forming a protective shell of zein, effectively prevented clusters from aggregating or growing into larger nanoparticles. The synergistic effect of the bimetal promotes the ECL emission, making this nanoscale material an ideal ECL probe. GO-PANI, which effectively promoting the production of sulfate radicals of the co-reactant and significantly increasing the ECL strength, was a good sensing platform for antibody immobilization. Consequently, we constructed an ECL sensor with GO-PANI as the sensing platform and Au-Ag BNCs@zein as the ECL probe, with a detection range of 0.001-100 U mL-1 and a detection limit of 0.0003 U mL-1, provided a strong support for the sensor for future CA15-3 detection applications.

High-level ab initio evidence of bipyramidal Cu5 clusters as fluxional Jahn-Teller molecules

Novel highly selective synthesis techniques have enable the production of atomically precise monodisperse metal clusters (AMCs) of subnanometer size. These AMCs exhibit 'molecule-like' structures that have distinct physical and chemical properties, significantly different from those of nanoparticles and bulk material. In this work, we study copper pentamer Cu5 clusters as model AMCs by applying both density functional theory (DFT) and high-level (wave-function-based) ab initio methods, including those which are capable of accounting for the multi-state multi-reference character of the wavefunction at the conical intersection (CI) between different electronic states and augmenting the electronic basis set till achieving well-converged energy values and structures. After assessing the accuracy of a high-level multi-multireference ab initio protocol for the well-known Cu3 case, we apply it to demonstrate that bypiramidal Cu5 clusters are distorted Jahn-Teller (JT) molecules. The method is further used to evaluate the accuracy of single-reference approaches, finding that the coupled cluster singles and doubles and perturbative triples CCSD(T) method delivers the results closer to our ab initio predictions and that dispersion-corrected DFT can outperform the CCSD method. Finally, we discuss how JT effects and, more generally, conical intersections, are intimately connected to the fluxionality of AMCs, giving them a 'floppy' character that ultimately facilitates their interaction with environmental molecules and thus enhances their functioning as catalysts.

Discovery and Feasibility Study of Medical Fluorophore 33 as a Novel Theranostic Agent

Fluorescent dyes have garnered significant attention as theranostic platforms owing to their inherent characteristics. In this study, we present the discovery of Medical Fluorophore 33 (MF33), a novel and potent theranostic agent with a phenaleno-isoquinolinium salt structure that can serve as a cancer therapeutic strategy. The synthesis of MF33 is readily achievable through a simple Rh(III)-catalyzed reaction. Moreover, MF33 displayed strong fluorescence signals, excellent microsomal stability, and high biocompatibility in vivo. It induces significant apoptosis in cancer cells via the p53/p21/caspase-3 signaling pathway, leading to selective cytotoxicity in various cancer cells. In vivo fluorescence imaging with MF33 enabled the visualization of sentinel lymph nodes in living mice. Notably, repeated intraperitoneal administration of MF33 resulted in antitumor activity in mice with colorectal cancer. Collectively, our findings suggest that phenaleno-isoquinolinium salt-based MF33 is a viable theranostic agent for biomedical imaging and cancer treatment.

Development of Au8 nanocluster-based fluorescent strip immunosensor for sensitive detection of aflatoxin B1

Gold clusters with intriguing chemical/physical properties have great promise in applications such as sensing and bio-imaging due to their fascinating photoluminescence character. In this study, an immunofluorescence sensor based on levonorgestrel protected atomically precise Au₈ nanocluster (Au₈NC) for aflatoxin B₁ (AFB₁) detection was fabricated due to its strong carcinogenic and mutagenic effect on humans. The prepared polymer-Au₈NC nanospheres displayed bright luminescence and good stability in aqueous solution. The obtained AFB₁ fluorescent strip immunosensor achieved quantitative point-of-care detection of AFB₁ in less than 15 min, with high selectivity and detection limits down to 0.27 ng/mL. In addition, the recovery rates of AFB₁ from tea soup ranged from 96% to 105% with relative standard deviations less than 10%. This work not only realized high-sensitively fluorescent sensing for AFB₁, but also expanded the bio-applications of atomic-precise metal clusters.

Potential impact of various surface ligands on the cellular uptake and biodistribution characteristics of red, green, and blue emitting Cu nanoclusters

Surface functionalization has a prominent influence on tuning/manipulating the physicochemical properties of nanometer scaled materials. Ultrasmall sized nanoclusters with very few atoms have received enormous attention due to their bright fluorescence, biocompatibility, lower toxicity, good colloidal stability and strong photostability. These properties make them suitable for diagnostic applications. In this work, we intend to study the effect of surface functional ligands on their biodistribution both in vitro and in vivo organelle systems for bioimaging applications.

Controlling NIR-II emitting gold organic/inorganic nanohybrids with tunable morphology and surface PEG density for dynamic visualization of vascular dysfunction

Luminescent Au nanoparticles (AuNPs) and their organic/inorganic nanohybrids are of interest due to their favorable properties and promising biomedical applications. However, most existing AuNP-based hybrid nanostructures cannot satisfy high efficiency in synthesis, deep tissue penetration, and long blood circulation simultaneously, thus cannot be employed in dynamic monitoring of biomedical applications. In this paper, using Pluronic F127 as a template, we report a robust approach for one-pot synthesis of AuNP-based organic/inorganic nanohybrids (AuNHs) with bright luminescence in the second near-infrared (NIR-II) window, tunable shape, and controllable surface polyethylene glycol (PEG) density. The nanohybrids could be controlled from a necklace-like shape with a dense brush PEG configuration to a spherical structure with a brush PEG coating, which greatly impacts the in vivo biological behavior. Compared to spherical AuNHs, the necklace-shaped AuNHs present a higher quantum yield and longer blood circulation, which are superior to most of the individual AuNPs. With these outstanding features, the necklace-shaped AuNHs could achieve real-time, dynamic visualization of vascular dysfunction, capable of directing the precise administration of thrombolytics (a medicine for the breakdown of blood clots). These findings could provide a powerful guide for designing novel NIR-II nanoprobes toward in vivo dynamic information visualization.

Engineering Au44 Nanoclusters for NIR-II Luminescence Imaging-Guided Photoactivatable Cancer Immunotherapy

Immunotherapy is an advanced therapeutic strategy of cancer treatment but suffers from the issues of off-target adverse effects, lack of real-time monitoring techniques, and unsustainable response. Herein, an ultrasmall Au nanocluster (NC)-based theranostic probe is designed for second near-infrared window (NIR-II) photoluminescence (PL) imaging-guided phototherapies and photoactivatable cancer immunotherapy. The probe (Au44MBA26-NLG for short) is composed of atomically precise and NIR-II emitting Au44MBA26 NCs (here MBA denotes water-soluble 4-mercaptobenzoic acid) conjugated with immune checkpoint inhibitor 1-cyclohexyl-2-(5H-imidazo[5,1-a]isoindol-5-yl)ethanol (NLG919) via a singlet oxygen (1O2)-cleavable linker. Upon NIR photoirradiation, the Au44MBA26-NLG not only enables NIR-II PL imaging of tumors in deep tissues for guiding tumor therapy but also allows the leverage of photothermal property for cancer photothermal therapy (PTT) and the photogenerated 1O2 for photodynamic therapy (PDT) and releasing NLG919 for cancer immunotherapy. Such a multiple effect modulated by Au44MBA26-NLG prompts the proliferation and activation of effector T cells, upshifts systemic antitumor T-lymphocyte (T cell) immunity, and finally suppresses the growth of both primary and distant tumors in living mice. Overall, this study may provide a promising theranostic nanoplatform toward NIR-II PL imaging-guided phototherapies and photoactivatable cancer immunotherapy.

Evaluation of the time-dependent osteogenic activity of glycerol incorporated magnesium oxide nanoparticles in induced calvarial defects

Introduction

Magnesium-based biomaterials have been explored for their potential as bone healing materials, as a result of their outstanding biodegradability and biocompatibility. These characteristics make magnesium oxide nanoparticles (MgO NPs) a promising material for treating bone disorders. The purpose of this investigation is to assess the osteogenic activity of newly-developed locally administered glycerol-incorporated MgO NPs (GIMgO NPs) in rabbits' calvarial defects.

Materials and methods

Characterization of GIMgO was done by X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Bilateral calvarial defects were created in eighteen New Zealand Rabbits, of which they were divided into 3 groups with time points corresponding to 2, 4, and 6 weeks postoperatively (n = 6). One defect was implanted with absorbable gel foam impregnated with GIMgO NPs while the other was implanted with gel foam soaked with glycerol (the control). The defects were assessed using histological, Micro-Computed Tomography (Micro-CT), and histometric evaluation.

Results

The characterization of the GIMgO nanogel revealed the presence of MgO NPs and glycerol as well as the formation of the crystalline phase of the MgO NPs within the nanogel sample. The histological and micro-CT analysis showed time-dependent improvement of healing activity in the calvarial defects implanted with GIMgO NPs when compared to the control. Furthermore, the histometric analysis demonstrated a marked increase in the total area of new bone, connective tissue, new bone area and volume in the GIMgO NPs implanted site. Statistically, the amount of new bone formation was more significant at 6 weeks than at 2 and 4 weeks postoperatively in the calvarial defects implanted with GIMgO NPs as compared to the control.

Conclusion

The locally applied GIMgO NPs demonstrated efficacy in promoting bone formation, with more significant effects observed over an extended period. These findings suggest its suitability for clinical use as a therapeutic alternative to enhance bone healing.

Ultrasmall Coinage Metal Nanoclusters as Promising Theranostic Probes for Biomedical Applications

Ultrasmall coinage metal nanoclusters (NCs, <3 nm) have emerged as a novel class of theranostic probes due to their atomically precise size and engineered physicochemical properties. The rapid advances in the design and applications of metal NC-based theranostic probes are made possible by the atomic-level engineering of metal NCs. This Perspective article examines (i) how the functions of metal NCs are engineered for theranostic applications, (ii) how a metal NC-based theranostic probe is designed and how its physicochemical properties affect the theranostic performance, and (iii) how metal NCs are used to diagnose and treat various diseases. We first summarize the tailored properties of metal NCs for theranostic applications in terms of biocompatibility and tumor targeting. We focus our discussion on the theranostic applications of metal NCs in bioimaging-directed disease diagnosis, photoinduced disease therapy, nanomedicine, drug delivery, and optical urinalysis. Lastly, an outlook on the challenges and opportunities in the future development of metal NCs for theranostic applications is provided.

Promoting the healing of methicillin-resistant Staphylococcus aureus-infected wound by a multi-target antimicrobial AIEgen of 6-Aza-2-thiothymine-decorated gold nanoclusters

The use of conventional antibiotic therapies is in question owing to the emergence of drug-resistant pathogenic bacteria. Therefore, novel, highly efficient antibacterial agents to effectively overcome resistant bacteria are urgently needed. Accordingly, in this work, we described a novel class luminogen of 6-Aza-2-thiothymine-decorated gold nanoclusters (ATT-AuNCs) with aggregation-induced emission property that possessed potent antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA). Scanning electron microscopy was performed to investigate the interactions between ATT-AuNCs and MRSA. In addition, ATT-AuNCs exhibited excellent ROS generation efficiency and could effectively ablate MRSA via their internalization to the cells. Finally, tandem mass tag-labeling proteome analysis was carried out to investigate the differential expression proteins in MRSA strains. The results suggested that ATT-AuNCs killed MRSA cells through altering the expression of multiple target proteins involved in DNA replication, aminoacyl-tRNA synthesis, peptidoglycan and arginine biosynthesis metabolism. Parallel reaction monitoring technique was further used for the validation of these proteome results. ATT-AuNCs could also be served as a wound-healing agent and accelerate the healing process. Overall, we proposed ATT-AuNCs could serve as a robust antimicrobial aggregation-induced emission luminogen (AIEgen) that shows the ability to alter the activities of multiple targets for the elimination of drug-resistant bacteria.

Emerging ultrasmall luminescent nanoprobes for in vivo bioimaging

Photoluminescence (PL) imaging has become a fundamental tool in disease diagnosis, therapeutic evaluation, and surgical navigation applications. However, it remains a big challenge to engineer nanoprobes for high-efficiency in vivo imaging and clinical translation. Recent years have witnessed increasing research efforts devoted into engineering sub-10 nm ultrasmall nanoprobes for in vivo PL imaging, which offer the advantages of efficient body clearance, desired clinical translation potential, and high imaging signal-to-noise ratio. In this review, we present a comprehensive summary and contrastive discussion of emerging ultrasmall luminescent nanoprobes towards in vivo PL bioimaging of diseases. We first summarize size-dependent nano-bio interactions and imaging features, illustrating the unique attributes and advantages/disadvantages of ultrasmall nanoprobes differentiating them from molecular and large-sized probes. We also discuss general design methodologies and PL properties of emerging ultrasmall luminescent nanoprobes, which are established based on quantum dots, metal nanoclusters, lanthanide-doped nanoparticles, and silicon nanoparticles. Then, recent advances of ultrasmall luminescent nanoprobes are highlighted by surveying their latest in vivo PL imaging applications. Finally, we discuss existing challenges in this exciting field and propose some strategies to improve in vivo PL bioimaging and further propel their clinical applications.

Engineering Liganded Gold Nanoclusters as Efficient Theranostic Agents for Cancer Applications

Luminescent gold nanoclusters are rapidly gaining attention as efficient theranostic targets for imaging and therapeutics. Indeed, their ease of synthesis, their tunable optical properties and tumor targeting make them potential candidates for sensitive diagnosis and efficacious therapeutic applications. This concept highlights the key components for designing gold nanoclusters as efficient theranostics focusing on application in the field of oncology.

Surface Ligand Influences the Cu Nanoclusters as a Dual Sensing Optical Probe for Localized pH Environment and Fluoride Ion

Functional metal nanomaterials, especially in the nanocluster (NC) size regime, with strong fluorescence, aqueous colloidal stability, and low toxicity, necessitate their application potential in biology and environmental science. Here, we successfully report a simple cost-effective method for red-/green-color-emitting protein/amino-acid-mediated Cu NCs in an aqueous medium. As-synthesized Cu NCs were characterized through UV-Vis absorption spectroscopy, fluorescence spectroscopy, time-resolved photoluminescence, dynamic light scattering, zeta potential, transmission electron microscopy and X-ray photoelectron spectroscopy. The optical properties of both Cu NCs responded linearly to the variation in pH in the neutral and alkaline ranges, and a robust pH reversible nature (between pH 7 and 11) was observed that could be extended to rapid, localized pH sensor development. However, a contrasting pH response nature between protein-Cu NCs and amino acid-Cu NCs was recorded. The alteration in protein secondary structure and strong binding nature of the surfactants were suggested to explain this behavior. Furthermore, we investigated their use as an efficient optical probe for fluoride ion detection. The limit of detection for protein-Cu NCs is 6.74 µM, whereas the limit of detection for amino acid-Cu NCs is 4.67 µM. Thus, it is anticipated that ultrasmall Cu NCs will exhibit promise in biological and environmental sensing applications.

Ligand engineering of Au44 nanoclusters for NIR-II luminescent and photoacoustic imaging-guided cancer photothermal therapy

A theranostic probe was developed by conjugating NIR-II emitting Au44MBA26 nanoclusters with photothermal Cy7 molecules via click chemistry, achieving NIR-II luminescent and photoacoustic imaging-guided cancer photothermal therapy.

One-Step Synthesis of Peptide-Gold Nanoclusters with Tunable Fluorescence and Enhanced Gene Delivery Efficiency

In this study, peptide-gold nanoclusters with tunable fluorescence were prepared by a simple "one-pot" method, which were used for gene localization and delivery in vivo to achieve efficient intracellular colocalization, uptake, and transfection. The efficiency of pDNA transfection was up to 70.6%, and there was no obvious cytotoxicity. This study proves that the simple-composition and bio-friendly peptide-gold nanoclusters are promising gene delivery carriers and can provide a powerful theoretical and experimental basis for the application of peptide-metal nanocomplexes in gene delivery and other biomedicine fields.

Interaction of Atomically Precise Thiolated Copper Nanoclusters with Proteins: A Comparative Study

A facile synthesis of glutathione-stabilized copper nanoclusters (CuNCs) is carried out in H₂O/ tetrahydrofuran medium. The photophysical and morphological studies performed with as-synthesized CuNCs revealed the formation of green-emissive, stable, and smaller nanoclusters. The precise composition of these as-synthesized CuNCs was predicted with the aid of electrospray ionization mass spectrometry analysis as Cu₁₂(SG)₉. Furthermore, the systematic studies of the interaction of synthesized CuNCs with three plasmatic proteins, namely, bovine serum albumin (BSA), lysozyme (Lys), and hemoglobin (Hb) have been performed by using a series of spectroscopic studies. The conformational changes in these proteins upon interacting with CuNCs and their binding stoichiometries have been investigated from the combination of UV-visible and steady-state fluorescence measurements. The changes in the microenvironment of proteins caused by CuNCs were investigated by circular dichroism spectroscopy. Among these three proteins, BSA and Lys had a minor effect on the luminescence of CuNCs, which makes them suitable candidates for biological applications. There are no drastic changes in the microenvironment of NCs as well as proteins because of the possibilities of weak electrostatic and H-bonding interactions of CuNCs with BSA and Lys. The feasibility of strong metallophic interaction between the Fe²⁺ present in the heme group of Hb and Cu(I) or -S atoms present in the CuNCs brings considerable changes in the photophysical activity of CuNCs and their interactions with Hb. The functional groups on NCs as well as active amino acid residues present in proteins play a crucial role in determining their interactions. This work shed a piece of knowledge on designing NCs for specific biological applications.

Antibiofilm activity of ultra-small gold nanoclusters against Fusobacterium nucleatum in dental plaque biofilms

Pathogenic dental plaque biofilms are universal and harmful, which can result in oral infections and systemic diseases. Many conventional therapeutic methods have proven insufficient or ineffective against plaque biofilms. Therefore, new strategies are urgently needed. Fusobacterium nucleatum (F. nucleatum), a periodontal pathogen associated with a variety of oral and systemic diseases, is thought to be central to the development and structure of dental plaques. Here, ultra-small gold nanoclusters (AuNCs) were prepared. They exhibited potent antibacterial activity against F. nucleatum through enhanced destruction of bacterial membranes and generation of reactive oxygen species. Furthermore, due to their excellent penetration, the AuNCs could inhibit biofilm formation and destroy mature biofilms in vitro. Their antibiofilm efficacy was further confirmed in a mouse model, where they reduced biofilm accumulation and ameliorated inflammation. Meanwhile, the disruption of oral and gut microbiota caused by colonization of oral F. nucleatum could be partially restored through AuNCs treatment. Therefore, AuNCs could be considered as promising antibiofilm agents and have great potential in the clinical treatment of dental plaque.

Engineering Coinage Metal Nanoclusters for Electroluminescent Light-Emitting Diodes

Coinage metal nanoclusters (MNCs) are a new type of ultra-small nanoparticles on the sub-nanometer (typically < three nm) scale intermediate between atoms and plasmonic nanoparticles. At the same time, the ultra-small size and discrete energy levels of MNCs enable them to exhibit molecular-like energy gaps, and the total structure involving the metal core and surface ligand together leads to their unique properties. As a novel environmentally friendly chromophore, MNCs are promising candidates for the construction of electroluminescent light-emitting diodes (LEDs). However, a systematic summary is urgently needed to correlate the properties of MNCs with their influences on electroluminescent LED applications, describe the synthetic strategies of highly luminescent MNCs for LEDs’ construction, and discuss the general influencing factors of MNC-based electroluminescent LEDs. In this review, we first discuss relevant photoemissions of MNCs that may have major influences on the performance of MNC-based electroluminescent LEDs, and then demonstrate the main synthetic strategies of highly luminescent MNCs. To this end, we illustrate the recent development of electroluminescent LEDs based on MNCs and present our perspectives on the opportunities and challenges, which may shed light on the design of MNC-based electroluminescent LEDs in the near future.

The Atomically Precise Gold/Captopril Nanocluster Au25(Capt)18 Gains Anticancer Activity by Inhibiting Mitochondrial Oxidative Phosphorylation

Atomically precise gold nanoclusters (AuNCs) are an emerging class of quantum-sized nanomaterials with well-defined molecular structures and unique biophysical properties, rendering them highly attractive for biological applications. We set out to study the impact of different ligand shells of atomically similar nanoclusters on cellular recognition and response. To understand the effects of atomically precise nanoclusters with identical composition on cells, we selected two different water-soluble gold nanoclusters protected with captopril (Capt) and glutathione (GSH): Au₂₅(Capt)₁₈ (CNC) and Au₂₅(GSH)₁₈ (GNC), respectively. We demonstrated that a change of the ligand of the cluster completely changes its biological functions. Whereas both nanoclusters are capable of internalization, only CNC exhibits remarkable cytotoxicity, more specifically on cancer cells. CNC shows enhanced cytotoxicity by inhibiting the OXPHOS of mitochondria, possibly by inhibiting the ATP synthase complex of the electron transport chain (ETC), and by initiating the leakage of electrons into the mitochondrial lumen. The resulting increase in both mitochondrial and total cellular ROS triggers cell death indicated by the appearance of cellular markers of apoptosis. Remarkably, this effect of nanoclusters is independent of any external light source excitation. Our findings point to the prevailing importance of the ligand shell for applications of atomically precise nanoclusters in biology and medicine.

Conjugating AIE-featured AuAg nanoclusters with highly luminescent carbon dots for improved visible-light-driven antibacterial activity

Metal nanoclusters (NCs) have emerged as novel antibacterial agents featuring broad-spectrum antibacterial activity without drug resistance for bacteria, but suffer from fast antibacterial invalidation due to their consumption by bacteria. Herein we report the design of a visible-light-driven photodynamic antibacterial agent based on conjugating aggregation-induced emission (AIE)-featured AuAg NCs with highly luminescent carbon dots (CDs). The conjugation of CDs with AuAg NCs could not only enhance the visible-light harvest, but also promote charge carrier generation/separation via charge/energy transfer, leading to the production of abundant reactive oxygen species (ROS) for bacterial killing under visible-light irradiation. Consequently, the as-obtained CDs@AuAg NCs display excellent photodynamic antibacterial activity against both Gram-positive and Gram-negative bacteria with 4-5 orders of magnitude reduction in colony forming units, which is different from the conventional metal NC-based analogue relying on self-consumption for bacterial killing. In addition, the CDs@AuAg NCs are found to be free of cytotoxicity; the ROS capture experiments indicate that the photoproduced H₂O₂ by CDs@AuAg NCs is the main active species for bacterial killing, accounting for nearly 48% of the total antibacterial efficacy. This study provides a paradigm for the design of metal NC-based photodynamic antibacterial agents for diverse bactericidal applications.

Engineering colloidally stable, highly fluorescent and nontoxic Cu nanoclusters via reaction parameter optimization

Metal nanoclusters (NCs) composed of the least number of atoms (a few to tens) have become very attractive for their emerging properties owing to their ultrasmall size. Preparing copper nanoclusters (Cu NCs) in an aqueous medium with high emission properties, strong colloidal stability, and low toxicity has been a long-standing challenge. Although Cu NCs are earth-abundant and inexpensive, they have been comparatively less explored due to their various limitations, such as ease of surface oxidation, poor colloidal stability, and high toxicity. To overcome these constraints, we established a facile synthetic route by optimizing the reaction parameters, especially altering the effective concentration of the reducing agent, to influence their optical characteristics. The improvement of the photoluminescence intensity and superior colloidal stability was modeled from a theoretical standpoint. Moreover, the as-synthesized Cu NCs showed a significant reduction of toxicity in both in vitro and in vivo models. The possibility of using such Cu NCs as a diagnostic probe toward C. elegans was explored. Also, the extension of our approach toward improving the photoluminescence intensity of the Cu NCs on other ligand systems was demonstrated.

A facile synthetic strategy to engineer improved fluorescent quantum yield, colloidally stable, and low toxic Cu nanoclusters is introduced. These nanoclusters have the potential to be used as excellent bioimaging probes.

Multifunctional fluorescent gold nanoclusters with enhanced aggregation-induced emissions (AIEs) and excellent antibacterial effect for bacterial imaging and wound healing

To explore new alternatives to combat increasing risk of bacterial infection, in this work, a cationic antimicrobial peptide (HHC10) and glutathione (GSH) co-ligand protected ultra-small gold nanoclusters (Au NCs) was constructed by a simple one-pot method. The intrinsic luminescent property of GSH-protected Au NCs (Au_xGSH) endowed enhanced aggregation-induced emissions (AIEs) of co-ligand-protected Au NCs (Au_xGSH-HHC10), which exhibited a very strong orange luminescence. Based on the AIE effect, for one thing, Au_xGSH could be applied to rapidly and selectively detect Gram-positive bacteria. For another, Au_xGSH-HHC10 exhibited potential for multicolor imaging of both Gram-negative and Gram-positive bacteria. Besides, as-synthesized Au_xGSH-HHC10 could act as potent nanoantibiotics against both Gram-negative and Gram-positive bacteria, which could not only avoid drug tolerance but also be effective toward drug-resistance bacteria. The antibacterial mechanism indicated that the synergetic effect of the generation of reactive oxygen species (ROS), binding with DNA, and broad-spectrum antibacterial activity of HHC10 led to the membrane damage, depolarization, and interference of biological function, thus enhancing the antibacterial effect. More importantly, such an Au NCs could realize excellent therapeutic outcomes for wound healing in vivo, and showed good biocompatibility and biosafety toward health tissues. The results will provide a great potential for the application of Au NCs for imaging-guided antibacterial platform.

Inorganic Nanoparticles in Bone Healing Applications

Modern biomedicine aims to develop integrated solutions that use medical, biotechnological, materials science, and engineering concepts to create functional alternatives for the specific, selective, and accurate management of medical conditions. In the particular case of tissue engineering, designing a model that simulates all tissue qualities and fulfills all tissue requirements is a continuous challenge in the field of bone regeneration. The therapeutic protocols used for bone healing applications are limited by the hierarchical nature and extensive vascularization of osseous tissue, especially in large bone lesions. In this regard, nanotechnology paves the way for a new era in bone treatment, repair and regeneration, by enabling the fabrication of complex nanostructures that are similar to those found in the natural bone and which exhibit multifunctional bioactivity. This review aims to lay out the tremendous outcomes of using inorganic nanoparticles in bone healing applications, including bone repair and regeneration, and modern therapeutic strategies for bone-related pathologies.

Magnetic and near-infrared-II fluorescence Au-Gd nanoclusters for imaging-guided sensitization of tumor radiotherapy

The significant role of multifunctional nanoprobes with complementary advantages in magnetic and near-infrared-II (NIR-II, 1000-1700 nm) fluorescence properties has been documented in precision cancer theranostics. However, certain limitations, including the large size (>10 nm), low NIR-II fluorescence quantum yield (QY < 1.0%), and inefficient magnetic performance (relaxation rate < 5.0 s^-1 mM^-1) of nanoprobes, restrict their biomedical applications and clinical translation. Albumin-based biomineralization was adopted to prepare bright NIR-II Au NCs, which were further conjugated with DTPA and Gd ions to produce magnetic and NIR-II Au-Gd NCs. Albumin-based biomineralization helped to develop ultrasmall Au-Gd nanoclusters with ultrasmall size (∼2 nm), high NIR-II fluorescence QY (∼3.0%), and effective magnetic resonance imaging (MRI) performance (relaxation rate (r1) = 22.6 s^-1 mM^-1). On the one hand, Au-Gd NCs achieved NIR-II fluorescence and MRI dual-modal imaging of tumors with a high signal-to-background ratio (SBR = 8.2) in mice. On the other hand, their effective metabolism simultaneously through the kidney and liver minimized their toxicity in vivo. Moreover, compared to the control group, the survival time of tumor-bearing mice was extended by three times when Au-Gd NCs with high-Z elements were used to perform dual-modal imaging-guided sensitization of tumor radiotherapy. Thus, ultrasmall nanoprobes with complementary imaging modalities and therapeutic functions manifest great potential in cancer precision diagnosis and therapy.

Engineering Au Nanoclusters for Relay Luminescence Enhancement with Aggregation-Induced Emission

The research of aggregation-induced emission (AIE) has been growing rapidly for the design of highly luminescent materials, as exemplified by the library of AIE-active materials (or AIEgens) fabricated and explored for diverse applications in different fields. Herein, we reported a relay luminescence enhancement of luminescent Au nanoclusters (Au NCs) through AIE. In addition, we demonstrated the emergence of reduced aggregation-caused luminescence by adjusting the temperature of the Au NC solution. The key to induce this effect is to attach a thermosensitive polymer poly(N-isopropylacrylamide) (PNIPAAm) on the surface of Au NCs, which will shrink at high temperature. More interestingly, the as-synthesized Au NCs-PNIPAAm can self-assemble into vesicles, resulting in an obvious decrease in the luminescence intensity in aqueous solution. The combination of relay luminescence enhancement (by AIE) and luminescence decrease (induced by thermosensitive polymers) will be beneficial to the understanding and manipulation of the optical properties of Au NCs, paving the way for their practical applications.

Engineered Bacteria for Enhanced Radiotherapy against Breast Carcinoma

Radiotherapy is widely applied for multiple malignant tumors ablation in the clinic. However, redundant doses of X-rays might destroy normal tissue in the periphery of tumor sites. Here, we developed an integrated nanosystem (Bac@BNP) composed of engineered bacteria (Bac) and Bi₂S₃ nanoparticles (BNPs) for sensitizing radiotherapy. Bac could target and colonize in tumor sites alternatively, which overexpressed cytolysin A (ClyA) protein to regulate the cell cycle from a radioresistant phase to a radiosensitive phase. Simultaneously, peptide-modified BNPs, as a radiosensitizer with a high-Z element, was released from the surface of Bac owing to the matrix metalloproteinase-2 (MMP-2) response in the tumor microenvironment. Under X-ray irradiation, BNPs could enhance the radiotherapy sensitivity by triggering the intracellular generation of reactive oxygen species (ROS), coupled with DNA damage. In this constructed nanosystem, the combination of Bac@BNP and X-ray irradiation led to significant suppression of breast carcinoma in murine models with reduced side effects.

Gold Nanoclusters: Imaging, Therapy, and Theranostic Roles in Biomedical Applications

For the past two decades, atomic gold nanoclusters (AuNCs, ultrasmall clusters of several to 100 gold atoms, having a total diameter of <2 nm) have emerged as promising agents in the diagnosis and treatment of cancer. Owing to their small size, significant quantization occurs to their conduction band, which leads to emergent photonic properties and the disappearance of the plasmonic responses observed in larger gold nanoparticles. For example, AuNCs exhibit native luminescent properties, which have been well-explored in the literature. Using proteins, peptides, or other biomolecules as structural scaffolds or capping ligands, required for the stabilization of AuNCs, improves their biocompatibility, while retaining their distinct optical properties. This paved the way for the use of AuNCs in fluorescent bioimaging, which later developed into multimodal imaging combined with computer tomography and magnetic resonance imaging as examples. The development of AuNC-based systems for diagnostic applications in cancer treatment was then made possible by employing active or passive tumor targeting strategies. Finally, the potential therapeutic applications of AuNCs are extensive, having been used as light-activated and radiotherapy agents, as well as nanocarriers for chemotherapeutic drugs, which can be bound to the capping ligand or directly to the AuNCs via different mechanisms. In this review, we present an overview of the diverse biomedical applications of AuNCs in terms of cancer imaging, therapy, and combinations thereof, as well as highlighting some additional applications relevant to biomedical research.

The Multifarious Applications of Copper Nanoclusters in Biosensing and Bioimaging and Their Translational Role in Early Disease Detection

Nanoclusters possess an ultrasmall size, amongst other favorable attributes, such as a high fluorescence and long-term colloidal stability, and consequently, they carry several advantages when applied in biological systems for use in diagnosis and therapy. Particularly, the early diagnosis of diseases may be facilitated by the right combination of bioimaging modalities and suitable probes. Amongst several metallic nanoclusters, copper nanoclusters (Cu NCs) present advantages over gold or silver NCs, owing to their several advantages, such as high yield, raw abundance, low cost, and presence as an important trace element in biological systems. Additionally, their usage in diagnostics and therapeutic modalities is emerging. As a result, the fluorescent properties of Cu NCs are exploited for use in optical imaging technology, which is the most commonly used research tool in the field of biomedicine. Optical imaging technology presents a myriad of advantages over other bioimaging technologies, which are discussed in this review, and has a promising future, particularly in early cancer diagnosis and imaging-guided treatment. Furthermore, we have consolidated, to the best of our knowledge, the recent trends and applications of copper nanoclusters (Cu NCs), a class of metal nanoclusters that have been gaining much traction as ideal bioimaging probes, in this review. The potential modes in which the Cu NCs are used for bioimaging purposes (e.g., as a fluorescence, magnetic resonance imaging (MRI), two-photon imaging probe) are firstly delineated, followed by their applications as biosensors and bioimaging probes, with a focus on disease detection.

Photoluminescent nanocluster-based probes for bioimaging applications

In the continuous search for versatile and better performing probes for optical bioimaging and biosensing applications, many research efforts have focused on the design and optimization of photoluminescent metal nanoclusters. They consist of a metal core composed by a small number of atoms (diameter < 2-3 nm), usually coated by a shell of stabilizing ligands of different nature, and are characterized by molecule-like quantization of electronic states, resulting in discrete and tunable optical transitions in the UV-Vis and NIR spectral regions. Recent advances in their size-selective synthesis and tailored surface functionalization have allowed the effective combination of nanoclusters and biologically relevant molecules into hybrid platforms, that hold a large potential for bioimaging purposes, as well as for the detection and tracking of specific markers of biological processes or diseases. Here, we will present an overview of the latest combined imaging or sensing nanocluster-based systems reported in the literature, classified according to the different families of coating ligands (namely, peptides, proteins, nucleic acids, and biocompatible polymers), highlighting for each of them the possible applications in the biomedical field.

Studies of probe tip materials by atomic force microscopy: a review

As a tool that can test insulators' surface morphology and properties, the performance index of atomic force microscope (AFM) probes is the most critical factor in determining the resolution of microscopy, and the performance of probes varies in various modes and application requirements. This paper reviews the latest research results in metal, carbon nanotube, and colloidal probes and reviews their related methods and techniques, analyses the advantages and disadvantages of the improved probes compared with ordinary probes by comparing the differences in spatial resolution, sensitivity, imaging, and other performance aspects, and finally provides an outlook on the future development of AFM probes. This paper promotes the development of AFM probes in the direction of new probes and further promotes the broader and deeper application of scanning probe microscope (SPM).

Atomically precise metal nanoclusters meet metal-organic frameworks

Significant progress has been made in both fields of atomically precise metal nanoclusters (NCs) and metal-organic frameworks (MOFs) in recent years. A promising direction is to integrate these two classes of materials for creating unique composites with improved properties for catalysis and other applications. NCs incorporated with MOFs exhibit an optimized catalytic performance in many catalytic reactions, in which MOFs play a vital supporting role or as cocatalysts. In this Perspective, we first provide a brief summary of the methods that have been developed for the preparation of NCs/MOF composites and the characteristics of these strategies are analyzed. Following that, some recent works are highlighted to demonstrate the crucial role of MOF matrices in the enhancement of NCs catalytic properties. Finally, we outline some potentially important aspects for future work. This Perspective is in hopes of stimulating more interest in the research on the integration of NCs with MOFs toward functional materials.

Tyrosine-Templated Dual-Component Silver Nanomaterials Exhibit Photoluminescence and Versatile Antimicrobial Properties through ROS Generation

The role of small molecules in the preparation of metal nanomaterials generates considerable interest in the fields from materials science to interdisciplinary sciences. In this study, a small amino acid, l-tyrosine (Tyr), has been used as a ligand precursor for the preparation of silver nanomaterials (AgNMs) comprising a dual system: smaller silver nanoclusters (responsible exclusively for the photophysical properties) and larger silver nanoparticles (responsible exclusively for the antimicrobial properties). The luminescent properties of this AgNM system substantiate the role played by Tyr as a capping and a reducing agent outside the protein environment. An interesting feature of this report is the promising antimicrobial properties of the AgNMs against Saccharomyces cerevisiae, Candida albicans, Escherichia coli, and Bacillus cereus cell lines. The importance of this work is that this investigation demonstrates the combating ability of our AgNM system against pathogenic strains (C. albicans and B. cereus) as well. Moreover, the mechanistic aspects of the antimicrobial activity of the AgNMs were elucidated using various methods, such as propidium iodide staining, monitoring reactive oxygen species generation, leakage of proteins, DNA cleavage, etc. We propose that AgNM-mediated cytotoxicity in S. cerevisiae stems from the generation of singlet oxygen (¹O₂) species that create oxidative stress, disrupting the cell membrane and thereby resulting in leakage of proteins from the cells. This study can pave the way toward elucidating the role of a small molecule, Tyr, in the formation of NMs and describes the use of new NMs in potential antimicrobial applications.

Bioorthogonal chemistry in metal clusters: a general strategy for the construction of multifunctional probes for bioimaging in living cells and in vivo

Multifunctional bioimaging probes based on metal clusters have multiple characteristics of metal clusters and functional conjugates, and their development has broad application prospects in the fields of biomedical imaging and tumor diagnosis. However, current bioconjugation methods on metal clusters are time-consuming and have low reaction efficiency, which hinders the construction of bioimaging probes with multifunctional components. Here, we report a concise and promising design strategy to realize the simple and efficient introduction of functional conjugates through bioorthogonal reactions based on azido-functionalized metal clusters. Based on this strategy, taking the probe FA-Cu_C@BSA-Cy5 as an example, we demonstrated the design of a copper cluster-based multifunctional near-infrared (NIR) fluorescent probe and its real-time imaging application in vivo. Through the strain-promoted azide-alkyne cycloaddition (SPAAC) reaction, the tumor-specific targeting ligand folic acid (FA) and fluorophore (Cy5) can be chemically conjugated to azido-functionalized Cu_C@BSA-N₃ quickly and efficiently under biocompatible conditions. The prepared probe showed numerous advantages of metal clusters, including good stability, ultra-small particle size and low toxicity and rapid renal clearance. At the same time, FA-modified FA-Cu_C@BSA-Cy5 can specifically target KB cells with high FR expression, and in vivo fluorescence imaging shows higher tumor accumulation. The construction of the azido functional metal cluster platform can be extended to various metal clusters with functional probes and prodrugs, thereby providing more promising candidates for future medical diagnoses.

State of the Art and Perspectives on the Biofunctionalization of Fluorescent Metal Nanoclusters and Carbon Quantum Dots for Targeted Imaging and Drug Delivery

The interface of nanobio science and cancer nanomedicine is one of the most important current frontiers in research, being full of opportunities and challenges. Ultrasmall fluorescent metal nanoclusters (MNCs) and carbon quantum dots (CQDs) have emerged as promising fluorescent nanomaterials due to their unique physicochemical and optical properties, facile surface functionalization, good photostability, biocompatibility, and aqueous dispersity. These characteristics make them advantageous over conventional fluorophores such as organic dye molecules and semiconductor quantum dots (QDs) for the detection, diagnosis, and treatment of various diseases including cancer. Recently, researchers have focused on the biofunctionalization strategy of the MNCs and CQDs which can tailor their physicochemical and biological properties and, in turn, can empower these biofunctionalized nanoprobes for diverse applications including imaging, drug delivery, theranostics, and other biomedical applications. In this invited feature article, we first discuss some fundamental structural and physicochemical characteristics of the fluorescent biocompatible quantum-sized nanomaterials which have some outstanding features for the development of multiplexed imaging probes, delivery vehicles, and cancer nanomedicine. We then demonstrate the diverse surface engineering of these fluorescent nanomaterials with reactive target specific functional groups which can help to construct multifunctional nanoprobes with improved targeting capabilities having minimal toxicity. The promising future of the biofunctionalized fluorescent quantum-sized nanomaterials in the field of bioanalytical and biomedical research is elaborately demonstrated, showing selected recent works with relevant applications. This invited feature article finally ends with a short discussion of the current challenges and future prospects of the development of these bioconjugated/biofunctionalized nanomaterials to provide insight into this burgeoning field of MNC- and CQD-based diagnostics and therapeutic applications.

Fascinating MXene nanomaterials: emerging opportunities in the biomedical field

In recent years, there has been rapid progress in MXene research due to its distinctive two-dimensional structure and outstanding properties. Especially in biomedical applications, MXenes have attracted widespread favor with numerous studies on biosafety, bioimaging, therapy, and biosensing, although their development is still in the experimental stage. A comprehensive understanding of the current status of MXenes in biomedicine will promote their use in clinical applications. Here, we review advances in MXene research. First, we introduce the methods of synthesis, surface modification and functionalization of MXenes. Then, we summarize the biosafety and biocompatibility, paving the way for specific biomedical applications. On this basis, MXene nanostructures are described with respect to their use in antibacterial, bioimaging, cancer therapy, tissue regeneration and biosensor applications. Finally, we discuss MXene as a promising candidate material for further applications in biomedicine.

Nanoceutical Fabric Prevents COVID-19 Spread through Expelled Respiratory Droplets: A Combined Computational, Spectroscopic, and Antimicrobial Study

Centers for Disease Control and Prevention (CDC) warns the use of one-way valves or vents in face masks for potential threat of spreading COVID-19 through expelled respiratory droplets. Here, we have developed a nanoceutical cotton fabric duly sensitized with non-toxic zinc oxide nanomaterial for potential use as a membrane filter in the one-way valve for the ease of breathing without the threat of COVID-19 spreading. A detailed computational study revealed that zinc oxide nanoflowers (ZnO NFs) with almost two-dimensional petals trap SARS-CoV-2 spike proteins, responsible to attach to ACE-2 receptors in human lung epithelial cells. The study also confirmed significant denaturation of the spike proteins on the ZnO surface, revealing removal of the virus upon efficient trapping. Following the computational study, we have synthesized ZnO NF on a cotton matrix using a hydrothermal-assisted strategy. Electron-microscopic, steady-state, and picosecond-resolved spectroscopic studies confirm attachment of ZnO NF to the cotton (i.e., cellulose) matrix at the atomic level to develop the nanoceutical fabric. A detailed antimicrobial assay using Pseudomonas aeruginosa bacteria (model SARS-CoV-2 mimic) reveals excellent antimicrobial efficiency of the developed nanoceutical fabric. To our understanding, the nanoceutical fabric used in the one-way valve of a face mask would be the choice to assure breathing comfort along with source control of COVID-19 infection. The developed nanosensitized cloth can also be used as an antibacterial/anti CoV-2 washable dress material in general.

Nanoceutical Fabric Prevents COVID-19 Spread through Expelled Respiratory Droplets: A Combined Computational, Spectroscopic, and Antimicrobial Study

Centers for Disease Control and Prevention (CDC) warns the use of one-way valves or vents in face masks for potential threat of spreading COVID-19 through expelled respiratory droplets. Here, we have developed a nanoceutical cotton fabric duly sensitized with non-toxic zinc oxide nanomaterial for potential use as a membrane filter in the one-way valve for the ease of breathing without the threat of COVID-19 spreading. A detailed computational study revealed that zinc oxide nanoflowers (ZnO NFs) with almost two-dimensional petals trap SARS-CoV-2 spike proteins, responsible to attach to ACE-2 receptors in human lung epithelial cells. The study also confirmed significant denaturation of the spike proteins on the ZnO surface, revealing removal of the virus upon efficient trapping. Following the computational study, we have synthesized ZnO NF on a cotton matrix using a hydrothermal-assisted strategy. Electron-microscopic, steady-state, and picosecond-resolved spectroscopic studies confirm attachment of ZnO NF to the cotton (i.e., cellulose) matrix at the atomic level to develop the nanoceutical fabric. A detailed antimicrobial assay using Pseudomonas aeruginosa bacteria (model SARS-CoV-2 mimic) reveals excellent antimicrobial efficiency of the developed nanoceutical fabric. To our understanding, the nanoceutical fabric used in the one-way valve of a face mask would be the choice to assure breathing comfort along with source control of COVID-19 infection. The developed nanosensitized cloth can also be used as an antibacterial/anti CoV-2 washable dress material in general.

Ligand Design in Ligand-Protected Gold Nanoclusters

The design of surface ligands is crucial for ligand-protected gold nanoclusters (Au NCs). Besides providing good protection for Au NCs, the surface ligands also play the following two important roles: i) as the outermost layer of Au NCs, the ligands will directly interact with the exterior environment (e.g., solvents, molecules and cells) influencing Au NCs in various applications; and ii) the interfacial chemistry between ligands and gold atoms can determine the structures, as well as the physical and chemical properties of Au NCs. A delicate ligand design in Au NCs (or other metal NCs) needs to consider the covalent bonds between ligands and gold atoms (e.g., gold-sulfur (Au-S) and gold-phosphorus (Au-P) bond), the physics forces between ligands (e.g., hydrophobic and van der Waals forces), and the ionic forces between the functional groups of ligands (e.g., carboxylic (COOH) and amine group (NH₂ )); which form the underlying chemistry and discussion focus of this review article. Here, detailed discussions on the effects of surface ligands (e.g., thiolate, phosphine, and alkynyl ligands; or hydrophobic and hydrophilic ligands) on the synthesis, structures, and properties of Au NCs; highlighting the design principles in the surface engineering of Au NCs for diverse emerging applications, are provided.