Molecular reactivity of thiolate-protected noble metal nanoclusters: synthesis, self-assembly, and applications

Molecular Packing-Driven Manipulation of Aggregation Induced Emission in Gold Nanoclusters

A key limitation of supramolecular force-driven molecular assembly in aggregation-induced emission (AIE) materials is the need to precisely regulate molecular interactions within the assembly. Achieving such assemblies with in situ manipulable molecular arrangements could provide valuable insights into the role of molecular forces in AIE. Herein, by using glutathione-protected gold nanoclusters (AuNCs) as a model AIE material and a naturally occurring polyphenol, tannic acid (TA), as the assembling agent, we demonstrate that assemblies dominated by covalent bonds and hydrogen bonding show enhanced AIE, while those dominated by π-π stacking promote charge transfer, resulting in significant photoluminescence (PL) quenching. This phenomenon primarily stems from the oxidation of TA into smaller aromatic ring structures, leading to an increase in π-π interactions. The complete in situ oxidation of TA within the assembly induces a morphological transition from 3-D spherical to 2-D sheet-like structures due to the dominance of π-π interactions, consequently resulting in complete PL quenching of AuNCs. These findings highlight the critical role of molecular packing in modulating the AIE properties of AuNCs.

Innovative Synthesis of Au Nanoparticle-Trapped Flexible Macrocrystals: Achieving Stable Black Crystal Wires with Broadband Absorption

In optical materials, the development of absorbers for a wide spectrum is a focal point of research. A pivotal challenge lies in ensuring the stability and durability of optical absorbers, particularly at elevated temperatures. This study introduces a novel approach to creating absorbers with diverse colors, focusing on the synthesis and properties of black crystal wires. In contrast to black gold nanoparticle (Au NP) precipitates, which change color within hours under similar conditions, the method involves strategically trapping Au NPs within defects during the growth of single crystals. This results in black crystal wires that not only exhibit broadband absorption but also maintain exceptional stability even under prolonged exposure to high temperatures. The method also involves the controlled synthesis of colorless and red crystal wires. As a proof of concept, these stable black Au crystal wires demonstrate superior performance in photothermal conversion applications. The methodology, derived from the crystal growth process, presents a defect template that offers a novel approach to material design. Furthermore, these unique crystals, available in various colors, hold significant promise for a range of unexplored applications.

A molecular dynamics study on the ion-mediated self-assembly of monolayer-protected nanoclusters

We studied the effects of metal and molecular cations on the aggregation of atomically precise monolayer-protected nanoclusters (MPCs) in an explicit solvent using atomistic molecular dynamics simulations. While divalent cations such as Zn2+ and Cd2+ promote aggregation by forming ligand-cation-ligand bridges between the MPCs, molecular cations such as tetraethylammonium and cholinium inhibit their aggregation by getting adsorbed into the MPC's ligand shell and reducing the ligand's motion. Here, we studied the aggregation of Au25(SR)18 nanoclusters with two types of ligands, para-mercaptobenzoic acid and D-penicillamine, as prototypical examples.

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.

Bioinspired Surface Ligand Engineering Regulates Electron Transfers in Gold Clusterzymes to Enhance the Catalytic Activity for Improving Sensing Performance

Metal nanoclusters feature a hierarchical structure, facilitating their ability to mimic enzyme-catalyzed reactions. However, the lack of true catalytic centers, compounded by tightly bound surface ligands hindering electron transfers to substrates, underscores the need for universal rational design methodologies to emulate the structure and mechanisms of natural enzymes. Motivated by the electron transfer in active centers with specific chemical structures, by integrating the peroxidase cofactor Fe-TCPP onto the surface of glutathione-stabilized gold nanoclusters (AuSG), we engineered AuSG-Fe-TCPP clusterzymes with a remarkable 39.6-fold enhancement in peroxidase-like activity compared to AuSG. Fe-TCPP not only mimics the active center structure, enhancing affinity to H2O2, but also facilitates the electron transfer process, enabling efficient H2O2 activation. By exemplifying the establishment of a detecting platform for trace H2O2 produced by ultrasonic cleaners, we substantiate that the bioinspired surface-ligand-engineered electron transfer can improve sensing performance with a wider linear range and lower detection limit.

Mechanism Insight into Metal Exchange between Au25(SR)18-/Ag25(SR)18- Clusters and Metal Ions from Ab Initio Molecular Dynamics Simulations

The metal exchange reaction has emerged as an efficient method to synthesize ligand-protected alloy nanoclusters with precise compositions and structure. However, the understanding of the mechanism of these metal exchange processes is quite limited. Herein, the dynamic process of metal exchange of Au25(SR)18- and Ag25(SR)18- (R = CH3) nanoclusters with metal ions (Au+, Ag+, Cu2+, Cu+, Cd2+, and Hg2+) is investigated using ab initio molecular dynamics simulations. Computational results unveiled a multifaceted nature of the metal exchange process, dictated by several variables, including thermodynamic stability, electrochemical activity, metal affinity to ligand, and the coordination mode of metal ions. As a result of these factors, metal ions may either directly exchange with Au or Ag atoms on the icosahedral core surface by a "knock-off" mechanism or be stably adsorbed at the core-motif interface of Au25(SR)18- and Ag25(SR)18- nanoclusters. Meanwhile, we also discovered that counterions can promote adsorbed Ag and Cu atoms to diffuse into the gold core. Finally, the driving force of the galvanic reduction and antigalvanic reduction reactions is discussed. The formation of a more stable core-doping product nanocluster is the major driving force of metal exchange reactions.

Silver Cluster Assembled Materials: A Model-Driven Perspective on Recent Progress, with a Spotlight on Ag12 Cluster Assembly

The exploration of individual nanoclusters is rapidly advancing, despite stability concerns. To address this challenge, the assembly of cluster nodes through linker molecules has been successfully implemented. However, the linking of the cluster nodes itself introduces a multitude of possibilities, especially when additional factors come into play. While this method proves effective in enhancing material stability, the specific reasons behind its success remain elusive. In our laboratory, we have undertaken extensive studies on Ag cluster-assembled materials. So, here our goal is to establish a model system that allows for the discernment of various factors, eliminating unnecessary complexities during the linking approach. So, we hope that the systematic discourse presented in here will contribute significantly to future endeavors, helping to set clear priorities, and provide solutions to concerns that arise when working with a model system.

Assemble-Disassemble-Reassemble Dynamics in Copper Nanocluster-Based Superstructures

Assembling metal nanoclusters (MNCs) to form superstructures generates exciting photophysical properties distinct from those of their discrete precursors. Controlling the assembly process of MNCs and understanding the assembly-disassembly dynamics can have implications in achieving the reversible self-assembly of MNCs. The formation of self-assembled copper nanoclusters (CuNCs) as homogeneous superstructures and the underlying mechanisms governing such a process remain unexplored. Smart molecular imprinting of surface ligands can establish the forces necessary for the formation of such superstructures. Herein, we report highly luminescent, ordered superstructures of 4-phenylimidazole-2-thiol (4-PIT)-protected CuNCs with the help of l-ascorbic acid as a secondary ligand. Through a comprehensive spectroscopic analysis, we deciphered the mechanism of the self-assembly process, where the role of interligand H-bonding and C-H-π interactions was established. Notably, efficient reversibility of assembly-disassembly was demonstrated by re-establishing the interligand interactions and regenerating their photophysical and morphological signatures.

Gas-Phase Structures of [Au21(SR)14]- and [Au17(SR)10]- with Eight Electrons: Can They Support an Icosahedral Au13 Core?

A prototypical thiolate (RS)-protected gold cluster [Au25(SR)18]- has high stability due to specific geometric and electronic structures: an icosahedral (Ih) Au13 core with a closed electronic shell containing eight electrons is completely protected by six units of Au2(SR)3. Nevertheless, collisional excitation of [Au25(SR)18]- in a vacuum induces the sequential release of Au4(SR)4 to form [Au21(SR)14]- and [Au17(SR)10]- both containing eight electrons. To answer a naive question of whether these fragments bear an Ih Au13(8e) core, the geometrical structures of [Au21(SC3H7)14]- and [Au17(SC3H7)10]- in the gas phase were examined by the combination of anion photoelectron spectroscopy and density functional theory (DFT) calculation of simplified models of [Au21(SCH3)14]- and [Au17(SCH3)10]-. We concluded that [Au21(SC3H7)14]- retains a slightly distorted Ih Au13(8e) core, while [Au17(SC3H7)10]- has an amorphous Au13 core composed of triangular Au3, tetrahedral Au4, and prolate Au7 units. DFT calculations on putative species [Au19(SCH3)12]- and [Au18(SCH3)11]- suggested that the Ih Au13(8e) core undergoes dramatic structural deformation due to mechanical stress from μ2 ligation of only one RS.

Gold nanoclusters-based fluorescence sensor array for herbicides qualitative and quantitative analysis

Herbicides have been extensively used around the world, which poses a potential hazard to humans and wildlife. Accurate detection of herbicides is crucial for the environment and human health. Herein, a simple and sensitive fluorescence sensor array was constructed for discrimination and identification of herbicides. Fluorescent gold nanoclusters modified with 11-mercaptoundecanoic acid or reduced glutathione were prepared, respectively. Metal ions quenched the fluorescence of nanoclusters through coordination and leading to the aggregation of gold nanoclusters. The addition of auxin herbicides (2,4-dichlorophenoxyacetic acid, 2-methyl-4-chlorophenoxyacetic acid, decamba, picloram, quinclorac) restored the fluorescence of nanoclusters with different degrees. The mechanism study showed auxin herbicides can bind with metal ions and re-disperse the gold nanoclusters from the aggregation state. The "on-off-on" fluorescent sensor array was constructed basic on above detection mechanism. Combined with principal component analysis (PCA) and hierarchical cluster analysis (HCA) methods, auxin herbicides are well separated on 2D/3D PCA score plots and HCA dendrogram in the range of 40-500 μm. In addition, the fluorescence sensor array performed successful in detecting real samples and blind samples. The developed sensor system shows a promising in practical detection of herbicides.

Unraveling a Concerted Proton-Coupled Electron Transfer Pathway in Atomically Precise Gold Nanoclusters

Metal nanoclusters (MNCs) represent a promising class of materials for catalytic carbon dioxide and proton reduction as well as dihydrogen oxidation. In such reactions, multiple proton-coupled electron transfer (PCET) processes are typically involved, and the current understanding of PCET mechanisms in MNCs has primarily focused on the sequential transfer mode. However, a concerted transfer pathway, i.e., concerted electron-proton transfer (CEPT), despite its potential for a higher catalytic rate and lower reaction barrier, still lacks comprehensive elucidation. Herein, we introduce an experimental paradigm to test the feasibility of the CEPT process in MNCs, by employing Au18(SR)14 (SR denotes thiolate ligand), Au22(SR)18, and Au25(SR)18- as model clusters. Detailed investigations indicate that the photoinduced PCET reactions in the designed system proceed via an CEPT pathway. Furthermore, the rate constants of gold nanoclusters (AuNCs) have been found to be correlated with both the size of the cluster and the flexibility of the Au-S framework. This newly identified PCET behavior in AuNCs is prominently different from that observed in semiconductor quantum dots and plasmonic metal nanoparticles. Our findings are of crucial importance for unveiling the catalytic mechanisms of quantum-confined metal nanomaterials and for the future rational design of more efficient catalysts.

A Silver Nanocluster Assembled by a Superatomic Building Unit

A unique assembly of a two-electron superatom, [Ag10{S2P(OiPr)2}8], as a primary building unit in the construction of a supramolecule [Ag10{S2P(OiPr)2}8]2(μ-4,4'-bpy) through a 4,4'-bipyridine (4,4'-bpy) linker is reported. This approach is facilitated by an open site in the structure that allows for effective pairing. The assembled structure demonstrates a minimal solvatochromic shift across organic solvents with variable polarities, highlighting the influence of self-assembly on the photophysical properties of silver nanoclusters.

Fluorescent metal nanoclusters: prospects for photoinduced electron transfer and energy harvesting

Research on noble metal nanoclusters (MNCs) (elements with filled electron d-bands) is progressing forward because of the extensive and extraordinary chemical, optical, and physical properties of these materials. Because of the ultrasmall size of the MNCs (typically within 1-3 nm), they can be applied in areas of nearly all possible scientific domains. The greatest advantage of MNCs is the tunability that can be imposed, not only on their structures, but also on their chemical, physical, and biological properties. Nowadays, MNCs are very effectively used as energy donors and acceptors under suitable conditions and hence act as energy harvesters in solar cells, semiconductors, and biomarkers. In addition, ultrafast photoinduced electron transfer (PET) can be practised using MNCs under various circumstances. Herein, we have focused on the energy harvesting phenomena of Au-, Ag-, and Cu-based MNCs and elaborated on different ways to apply them.

In Situ Crystallization, Differential Growth, and Multicolor Emission of Silver Nanoclusters

The real-time monitoring of the stepwise growth process of the molecular crystal reveals a conclusive understanding of the morphological evolution, which otherwise remains elusive during the conventional crystallization processes. Herein, we report the in situ crystallization of silver nanoclusters (AgNCs) with special emphasis on their differential growth and multicolor emissive properties. A subtle variation of the methanol (MeOH) proportion in the reaction mixture induces the differential growth of these AgNCs, and thereby, a dramatic modulation in their optical properties was observed. Additionally, by increasing the temperature of the reaction (from a low temperature ice bath to 25 °C), an uncontrolled formation of AgNCs along with metallic silver nanoparticles (AgNPs) was observed, which was primarily induced by accelerating the reaction kinetics. We hope that this investigation comprehensively uncovers the serious bottlenecks of the conventional crystallization processes by showcasing systematic monitoring of structural evolution to the higher-ordered crystalline state.

Metal Nanoclusters as a Superior Polysulfides Immobilizer toward Highly Stable Lithium-Sulfur Batteries

Due to their high designability, unique geometric and electronic structures, and surface coordination chemistry, atomically precise metal nanoclusters are an emerging class of functional nanomaterials at the forefront of materials research. However, the current research on metal nanoclusters is mainly fundamental, and their practical applications are still uncharted. The surface binding properties and redox activity of Au24 Pt(PET)18 (PET: phenylethanethiolate, SCH2 CH2 Ph) nanoclusters are herein harnessed as an high-efficiency electrocatalyst for the anchoring and rapid conversion of lithium polysulfides in lithium-sulfur batteries (LSBs). Au24 Pt(PET)18 @G composites are prepared by using the large specific surface area, high porosity, and conductive network of graphene (G) for the construction of battery separator that can inhibit polysulfide shuttle and accelerate electrochemical kinetics. Resultantly, the LSB using a Au24 Pt(PET)18 @G-based separator presents a high reversible specific capacity of 1535.4 mA h g-1 for the first cycle at 0.2 A g-1 and a rate capability of 887 mA h g-1 at 5 A g-1 . After 1000 cycles at 5 A g-1 , the capacity is 558.5 mA h g-1 . This study is a significant step toward the application of metal nanoclusters as optimal electrocatalysts for LSBs and other sustainable energy storage systems.

Effect of Specific Heavy Doping of Silver Atoms into the Icosahedral Au13 on Electronic Structure and Catalytic Performance

The exploration of specific heavy doping of silver atoms into icosahedral Au13 clusters and their electronic structures and properties has been somewhat limited. Herein, we report two heavily Ag doped nanoclusters, [Au7Ag6(C7H4NOS)4(Dppf)3Cl]0 and [Au7Ag6(C7H4NOS)3(Dppf)3Cl](SbF6) (Au7Ag6-0 and Au7Ag6-1, respectively) [C7H4NOSH = 2-mercaptobenzoxazole, and Dppf = 1,1'-bis(diphenylphosphino)ferrocene]. The electronic structures and superatomic orbitals of nanoclusters were determined by density functional theory (DFT) calculations, and the energy degeneracy of the superatomic orbitals of Au7Ag6-1 is higher than that of Au7Ag6-0. Transient absorption spectroscopy was performed, revealing that Au7Ag6-0 significantly extends the excited-state lifetime. Both nanoclusters were supported on activated carbon for the oxygen reduction reaction. DFT calculations confirm that the catalytic activities mainly stem from the carbon atom of ferrocene rather than the iron atom. This study not only sheds light on the preparation of icosahedral alloy clusters but also provides insights into the regulation of icosahedral superatomic structure and electrocatalytic properties.

Activity of Different AunSn+1 Staples in the Ligand Exchange of Au23(SR)16- with a Single Foreign Thiolate Ligand

Ligand exchange has been widely used to synthesize novel thiolated gold nanoclusters and to regulate their specific properties. Herein, density functional theory (DFT) calculations were conducted to investigate the kinetic profiles of the ligand exchange of the [Au23(SCy)16]- nanocluster with an aromatic thiolate (2-napthalenethiol). The three types of staple motifs (i.e., trimetallic Au3S4, monometallic AuS2, and the bridging thiolates) of the Au23 cluster precursor could be categorized into eight groups of S sites with different chemical environments. The ligand exchange of all of them occurs favorably via the SN1-like pathway, with one site starting with the Au-S dissociation and seven other sites starting with the H-transfer steps. By contrast, the SN2-like pathway (i.e., the synergistic SCy-to-SAr exchange prior to the H-transfer step) is unlikely in the target systems. Meanwhile, the Au-S bond on the capping Au atom of the bicapped icosahedral Au15 core is the most active one, while the S sites on Au3S4 (except for the one remote from the metallic core) are all competitive exchanging sites. The ligand exchange activity of the bridging thiolate and the remote S site on Au3S4 is significantly less reactive. The calculation results correlate with the multiple ligand exchange within only a few minutes and the preferential etching of the AuS2 staple with the foreign ligands reported in earlier experiments. The relative activity of different staples might be helpful in elucidating the inherent principles in the ligand exchange-induced size-evolution of metal nanoclusters.

Recent developments in the investigation of driving forces for transforming coinage metal nanoclusters

Metal nanoclusters serve as an emerging class of modular nanomaterials. The transformation of metal nanoclusters has been fully reflected in their studies from every aspect, including the structural evolution analysis, physicochemical property regulation, and practical application promotion. In this review, we highlight the driving forces for transforming atomically precise metal nanoclusters and summarize the related transforming principles and fundamentals. Several driving forces for transforming nanoclusters are meticulously reviewed herein: ligand-exchange-induced transformations, metal-exchange-induced transformations, intercluster reactions, photochemical transformations, oxidation/reduction-induced transformations, and other factors (intrinsic instability, pH, temperature, and metal salts) triggering transformations. The exploitation of transforming principles to customize the preparations, structures, physicochemical properties, and practical applications of metal nanoclusters is also disclosed. At the end of this review, we provide our perspectives and highlight the challenges remaining for future research on the transformation of metal nanoclusters. Our intended audience is the broader scientific community interested in metal nanoclusters, and we believe that this review will provide researchers with a comprehensive synthetic toolbox and insights on the research fundamentals needed to realize more cluster-based nanomaterials with customized compositions, structures, and properties.

Ligand effect on switching the rate-determining step of water oxidation in atomically precise metal nanoclusters

The ligand effects of atomically precise metal nanoclusters on electrocatalysis kinetics have been rarely revealed. Herein, we employ atomically precise Au₂₅ nanoclusters with different ligands (i.e., para-mercaptobenzoic acid, 6-mercaptohexanoic acid, and homocysteine) as paradigm electrocatalysts to demonstrate oxygen evolution reaction rate-determining step switching through ligand engineering. Au₂₅ nanoclusters capped by para-mercaptobenzoic acid exhibit a better performance with nearly 4 times higher than that of Au₂₅ NCs capped by other two ligands. We deduce that para-mercaptobenzoic acid with a stronger electron-withdrawing ability establishes more partial positive charges on Au(I) (i.e., active sites) for facilitating feasible adsorption of OH^- in alkaline media. X-ray photo-electron spectroscopy and theoretical study indicate a profound electron transfer from Au(I) to para-mercaptobenzoic acid. The Tafel slope and in situ Raman spectroscopy suggest different ligands trigger different rate-determining step for these Au₂₅ nanoclusters. The mechanistic insights reported here can add to the acceptance of atomically precise metal nanoclusters as effective electrocatalysts.

Amorphous Copper-Based Nanoparticles with Clusterization-Triggered Phosphorescence for Ultrasensing 2,4,6-Trinitrotoluene

Amorphous metal-based nanostructures have attracted great attention recently due to their facilitative electron transfer and abundant reactive sites, whereas it remains enigmatic as to whether amorphous copper-based nanoparticles (CuNPs) can be achieved. Here, for synthesizing amorphous CuNPs, glutathione is adopted as a ligand to inhibit the nucleation and crystallization process via its electrostatic repulsion. By subtly tailoring the solvent polarity, not only can amorphous glutathione-functionalized CuNPs (GSH-CuNPs) with phosphorescent performance be achieved after transferring the non-conjugation of GSH ligand to through-space conjugation, namely clusterization-triggered emission, but also the phosphorescence-off of GSH-CuNPs toward 2,4,6-trinitrotoluene (TNT) can be realized by the photoinduced electron-transfer process through the hydrogen bond channel, which is established between carboxyl and amino groups of GSH-CuNPs with the nitryl group of TNT. Benefitting from the intrinsic superiorities of the amorphous CuNPs, desired phosphorescence and detection performances of GSH-CuNPs toward airborne TNT microparticulates are undoubtedly realized, including high quantum yield (13.22%), excellent specificity in 33 potential interferents, instantaneous response, and ultralow detection limit (1.56 pg). The present GSH-CuNPs are expected to stretch amorphous metal-based nanostructures and deepen the insights into amorphous materials for optical detection.

Metal-Ligand Interactions and Their Roles in Controlling Nanoparticle Formation and Functions

ConspectusFunctional nanoparticles (NPs) have been studied extensively in the past decades for their unique nanoscale properties and their promising applications in advanced nanosciences and nanotechnologies. One critical component of studying these NPs is to prepare monodisperse NPs so that their physical and chemical properties can be tuned and optimized. Solution phase reactions have provided the most reliable processes for fabricating such monodisperse NPs in which metal-ligand interactions play essential roles in the synthetic controls. These interactions are also key to stabilizing the preformed NPs for them to show the desired electronic, magnetic, photonic, and catalytic properties. In this Account, we summarize some representative organic bipolar ligands that have recently been explored to control NP formation and NP functions. These include aliphatic acids, alkylphosphonic acids, alkylamines, alkylphosphines, and alkylthiols. This ligand group covers metal-ligand interactions via covalent, coordination, and electrostatic bonds that are most commonly employed to control NP sizes, compositions, shapes, and properties. The metal-ligand bonding effects on NP nucleation rate and growth can now be more thoroughly investigated by in situ spectroscopic and theoretical studies. In general, to obtain the desired NP size and monodispersity requires rational control of the metal/ligand ratios, concentrations, and reaction temperatures in the synthetic solutions. In addition, for multicomponent NPs, the binding strength of ligands to various metal surfaces needs to be considered in order to prepare these NPs with predesigned compositions. The selective ligand binding onto certain facets of NPs is also key to anisotropic growth of NPs, as demonstrated in the synthesis of one-dimensional nanorods and nanowires. The effects of metal-ligand interactions on NP functions are discussed in two aspects, electrochemical catalysis for CO₂ reduction and electronic transport across NP assemblies. We first highlight recent advances in using surface ligands to promote the electrochemical reduction of CO₂. Several mechanisms are discussed, including the modification of the catalyst surface environment, electron transfer through the metal-organic interface, and stabilization of the CO₂ reduction intermediates, all of which facilitate selective CO₂ reduction. These strategies lead to better understanding of molecular level control of catalysis for further catalyst optimization. Metal-ligand interaction in magnetic NPs can also be used to control tunneling magnetoresistance properties across NPs in NP assemblies by tuning NP interparticle spacing and surface spin polarization. In all, metal-ligand interactions have yielded particularly promising directions for tuning CO₂ reduction selectivity and for optimizing nanoelectronics, and the concepts can certainly be extended to rationalize NP engineering at atomic/molecular precision for the fabrication of sensitive functional devices that will be critical for many nanotechnological applications.

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.

Dissociative reactions of [Au25(SR)18]- at copper oxide nanoparticles and formation of aggregated nanostructures

Reactions between nanoclusters (NCs) have been studied widely in the recent past, but such processes between NCs and metal-oxide nanoparticles (NPs), belonging to two different size ranges, have not been explored earlier. For the first time, we demonstrate the spontaneous reactions between an atomically precise NC, [Au₂₅(PET)₁₈]^- (PET = 2-phenylethanethiolate), and polydispersed copper oxide nanoparticles with an average diameter of 50 nm under ambient conditions. These interparticle reactions result in the formation of alloy NCs and copper-doped NC fragments, which assemble to form nanospheres at the end of the reaction. High-resolution electrospray ionization mass spectrometry (ESI MS), transmission electron microscopy (HR-TEM), electron tomography, and X-ray photoelectron spectroscopy (XPS) studies were performed to understand the structures formed. The results from our study show that interparticle reactions can be extended to a range of chemical systems, leading to diverse alloy NCs and self-assembled colloidal superstructures.

A luminescent Cu4 cluster film grown by electrospray deposition: a nitroaromatic vapour sensor

We present the fabrication and use of a film of a carborane-thiol-protected tetranuclear copper cluster with characteristic orange luminescence using ambient electrospray deposition (ESD). Charged microdroplets of the clusters produced by an electrospray tip deposit the clusters at an air-water interface to form a film. Different microscopic and spectroscopic techniques characterized the porous surface structure of the film. Visible and rapid quenching of the emission of the film upon exposure to 2-nitrotoluene (2-NT) vapours under ambient conditions was observed. Density functional theory (DFT) calculations established the favourable binding sites of 2-NT with the cluster. Desorption of 2-NT upon heating recovered the original luminescence, demonstrating the reusability of the sensor. Stable emission upon exposure to different organic solvents and its quenching upon exposure to 2,4-dinitrotoluene and picric acid showed selectivity of the film to nitroaromatic species.

A dual-signal fluorometric and colorimetric sensing platform based on gold-platinum bimetallic nanoclusters for the determination of β-galactosidase activity

Herein, a novel dual-signal sensing system for the determination of β-galactosidase (β-Gal) activity was established, which was based on a dual-emission probe assembled from gold-platinum bimetallic nanoclusters (Au-Pt NCs) and rhodamine B. Under the catalysis of β-Gal, 4-nitrophenyl β-D-galactopyranoside (PNPG) was rapidly hydrolyzed to generate p-nitrophenol (PNP), which has an obvious UV absorption peak at 400 nm. The hydrolyzed product PNP can quench the fluorescence of Au-Pt NCs effectively by inner filter effect (IFE), and PNP had no impact on the fluorescence of rhodamine B, which will change the emission intensity ratio of Au-Pt NCs and rhodamine B. Therefore, the ratiometric fluorescent and colorimetric dual-signal sensor based on Au-Pt NCs and rhodamine B was successfully constructed for sensitive detection of β-Gal activity. The linear detection range for the ratiometric fluorescence and colorimetric methods were 2.5-25 U/L and 15-55 U/L with detection limits of 1.2 U/L and 5.2 U/L, respectively. The developed assay method has been used for quantitative detection of β-Gal in spiked serum samples and showed good performance. And the detection platform has high reliability and excellent selectivity, which opens a new avenue for the further application of Au-Pt NCs in chemical sensing and biological analysis.

Luminescent [CO2@Ag20(SAdm)10(CF3COO)10(DMA)2] nanocluster: synthetic strategy and its implication towards white light emission

Owing to the quantized size and associated discrete energy levels, atomically precise silver nanoclusters (Ag NCs) hold great potential for designing functional luminescent materials. However, the thermally activated non-radiative transition of Ag(I)-based NCs has faded the opportunities. To acquire the structurally rigid architecture of cluster nodes for constraining such transitions, a new synthetic approach is unveiled here that utilizes a neutral template as a cluster-directing agent to assemble twenty Ag(I) atoms that ensure the maximum number of surface-protecting ligand attachment possibilities in a particular solvent medium. The solvent polarity triggers the precise structural design to circumvent the over-reliance of the templates, which results in the formation of [CO₂@Ag₂₀(SAdm)₁₀(CF₃COO)₁₀(DMA)₂] NC (where SAdm = 1-adamantanethiolate and DMA = N,N-dimethylacetamide) exhibiting an unprecedented room-temperature photoluminescence emission. The high quantum yield of the generated blue emission ensures its candidature as an ideal donor for artificial light-harvesting system design, and it is utilized with the two-step sequential energy transfer process, which finally results in the generation of ideal white light. For implementing perfect white light emission, the required chromophores in the green and red emission regions were chosen based on their effective spectral overlap with the donor components. Due to their favorable energy-level distribution, excited state energy transfers occurred from the NC to β-carotene at the initial step, then from the conjugate of the NC and β-carotene to another chromophore, Nile Blue, at the second step via a sequential Förster resonance energy transfer pathway.

Tree-based machine learning models assisted fluorescent sensor array for detection of metal ions based on silver nanocluster probe

The growing concern over heavy metal pollution and its impact on the environment and human health has led to a proliferation of research on the detection and differentiation of heavy metal ions. A novel fluorescent sensor array utilizing only one single Ag-nanoclusters (Ag NCs) was developed for the efficient detection of six metal ions. The Ag NCs probe was prepared by using poly(methyl vinyl ether-alt-maleic acid) (PMVEM) as the ligand and has different fluorescence properties in water and dimethyl sulfoxide (DMSO). The interaction between metal ions and Ag NCs resulted in a characteristic fluorescence variation pattern which was subsequently analyzed using various tree-based machine learning models. We have compared different combinations of classification models and pre-processing methods of which the K-Nearest Neighbors Classifier with the first five linear discriminants has the highest accuracy. Through the integration of concentration models within a tree-based pipeline optimization framework, six unique concentration regression models were selected for each metal ion. In addition, the developed sensor array could identify metal ions in binary mixtures. And it still kept high accuracy for the classification of six target metal ions in river water. In conclusion, the proposed framework was found to be effective in the detection of heavy metal ions in environmental samples, thus providing a promising approach for addressing heavy metal pollution.

Precision Nanocluster-Based Toroidal and Supertoroidal Frameworks Using Photocycloaddition-Assisted Dynamic Covalent Chemistry

Atomically precise nanoclusters (NCs) have recently emerged as ideal building blocks for constructing self-assembled multifunctional superstructures. The existing structures are based on various non-covalent interactions of the ligands on the NC surface, resulting in inter-NC interactions. Despite recent demonstrations on light-induced reversible self-assembly, long-range reversible self-assembly based on dynamic covalent chemistry on the NC surface has yet to be investigated. Here, it is shown that Au₂₅ NCs containing thiolated umbelliferone (7-hydroxycoumarin) ligands allow [2+2] photocycloaddition reaction-induced self-assembly into colloidal-level toroids. The toroids upon further irradiation undergo inter-toroidal reaction resulting in macroscopic supertoroidal honey-comb frameworks. Systematic investigation using electron microscopy, atomic force microscopy (AFM), and electron tomography (ET) suggest that the NCs initially form spherical aggregates. The spherical structures further undergo fusion resulting in toroid formation. Finally, the toroids fuse into macroscopic honeycomb frameworks. As a proof-of-concept, a cross-photocycloaddition reaction between coumarin-tethered NCs and an anticancer drug (5-fluorouracil) is demonstrated as a model photo-controlled drug release system. The model system allows systematic loading and unloading of the drug during the assembly and disassembly under two different wavelengths. The results suggest that the dynamic covalent chemistry on the NC surface offers a facile route for hierarchical multifunctional frameworks and photocontrolled drug release.

Superlattice-based Plasmonic Catalysis: Concentrating Light at the Nanoscale to Drive Efficient Nitrogen-to-Ammonia Fixation at Ambient Conditions

Plasmonic catalysis promises green ammonia synthesis but is limited by the need for co-catalysts and poor performances due to weak electromagnetic field enhancement. Here, we use two-dimensional plasmonic superlattices with dense electromagnetic hotspots to boost ambient nitrogen-to-ammonia photoconversion without needing co-catalyst. By organizing Ag octahedra into a square superlattice to concentrate light, the ammonia formation is enhanced by ≈15-fold and 4-fold over hexagonal superlattice and disorganized array, respectively. Our unique catalyst achieves superior ammonia formation rate and apparent quantum yield up to ≈15-fold and ≈10³ -fold, respectively, better than traditional designs. Mechanistic investigations reveal the abundance of intense plasmonic hotspots is crucial to promote hot electron generation and transfer for nitrogen reduction. Our work offers valuable insights to design electromagnetically hot plasmonic catalysts for diverse chemical and energy applications.

Solvent-mediated precipitating synthesis and optical properties of polyhydrido Cu13 nanoclusters with four vertex-sharing tetrahedrons

Structurally defined metal nanoclusters facilitate mechanism studies and promote functional applications. However, precisely constructing copper nanoclusters remains a long-standing challenge in nanoscience. Developing new efficient synthetic strategies for Cu nanoclusters is highly desirable. Here, we propose a solvent-mediated precipitating synthesis (SMPS) to prepare Cu₁₃H₁₀(SR)₃(PPh₃)₇ nanoclusters (H-SR = 2-chloro-4-fluorobenzenethiol). The obtained Cu₁₃ nanoclusters are high purity and high yield (39.5%, based on Cu atom), proving the superiority of the SMPS method. The Cu₁₃ nanoclusters were comprehensively studied via a series of characterizations. Single crystal X-ray crystallography shows that the Cu₁₃ nanoclusters contain a threefold symmetry axis and the Cu₁₃ kernel is protected by a monolayer of ligands, including PPh₃ and thiolates. Unprecedentedly, the aesthetic Cu₁₃ kernel is composed of four vertex-sharing tetrahedrons, rather than the common icosahedral or cuboctahedral M₁₃. The intramolecular π⋯π interactions between thiolates and PPh₃ on the surface contribute to the stable configuration. Furthermore, electrospray ionization mass spectrometry (ESI-MS) and nuclear magnetic resonance (NMR) revealed the existence of ten hydrides, including four types of hydrides. Density functional theory (DFT) calculations without simplifying the ligands simulated the location of the 10 hydrides in the crystal structure. Additionally, the steady-state ultraviolet-visible absorption and fluorescence spectra of the Cu₁₃ nanoclusters exhibit unique optical absorbance and photoluminescence. The ultrafast relaxation dynamics were also studied via transient absorption spectroscopy, and the three decay components are attributed to the relaxation pathways of internal conversion, structural relaxation and radiative relaxation. This work provides not only a novel SMPS strategy to efficiently synthesize Cu₁₃ nanoclusters, but also a better insight into the structural characteristics and optical properties of the Cu nanoclusters.

Surface Site-Specific Replacement for Catalysis Selectivity Switching

Surface atom replacement in materials without other composition/structure changes is challenging but is important for fundamental scientific research and for practical applications. In particular, for nanoparticles including nanoclusters, surface metal site-specific replacement with atomic precision has not yet been achieved. In this study, we for the first time achieved surface site-specific antigalvanic replacement with the remaining composition/structure and surface replacement-dependent selectivity in the electrocatalytic reduction of CO₂. Density functional theory (DFT) calculations describe the catalysis selectivity switch induced by replacing Ag with Cu and explain why Cu replacement facilitates C₂ production. Also, CO₂ electroreduction to C₂ on well-defined metal nanoclusters is first reported in this study.

Effects of ligand tuning and core doping of atomically precise copper nanoclusters on CO2 electroreduction selectivity

Atomically precise nanoclusters (NCs) provide opportunities for correlating the structure and electrocatalytic properties at atomic level. Herein, we report the single-atom doping effect and ligand effect on CO₂ electroreduction (eCO₂RR) by comparing monogold-doped Au₁Cu₂₄ and homocopper Cu₂₅ NCs protected by triphenylphosphine or/and tris(4-fluorophenyl)phosphine. Catalytic results revealed that the electronic distribution of Cu₂₅ NCs is enormously contracted by doping Au atoms, entitling it to exhibit the unique inhibition of hydrogen evolution reaction. And the inductive effect of ligand strongly favors the formation of formate in eCO₂RR. Overall, this work will provide guidance for the rational design of the copper-based catalysts in the eCO₂RR.

Structured copper-hydride nanoclusters provide insight into the surface-vacancy-defect to non-defect structural evolution

Exploring the structural evolution of clusters with similar sizes and atom numbers induced by the removal or addition of a few atoms contributes to a deep understanding of structure-property relationships. Herein, three well-characterized copper-hydride nanoclusters that provide insight into the surface-vacancy-defect to non-defect structural evolution were reported. A surface-defective copper hydride nanocluster [Cu₂₈(S-c-C₆H₁₁)₁₈(PPh₂Py)₃H₈]²⁺ (Cu₂₈-PPh₂Py for short) with only one C ₁ symmetry axis was synthesized using a one-pot method under mild conditions, and its structure was determined. Through ligand regulation, a 29^th copper atom was inserted into the surface vacancy site to give two non-defective copper hydride nanoclusters, namely [Cu₂₉(SAdm)₁₅Cl₃(P(Ph-Cl)₃)₄H₁₀]⁺ (Cu₂₉-P(Ph-Cl)₃ for short) with one C ₃ symmetry axis and (Cu₂₉(S-c-C₆H₁₁)₁₈(P(Ph-^pMe)₃)₄H₁₀)⁺ (Cu₂₉-P(Ph-Me)₃ for short) with four C ₃ symmetry axes. The optimized structures show that the 10 hydrides cap four triangular and all six square-planar structures of the cuboctahedral Cu₁₃ core of Cu₂₉-P(Ph-Me)₃, while the 10 hydrides cap four triangular and six square-planar structures of the anti-cuboctahedral Cu₁₃ core of Cu₂₉-P(Ph-Cl)₃, with the eight hydrides in Cu₂₈-PPh₂Py capping four triangular and four square planar-structures of its anti-cuboctahedral Cu₁₃ core. Cluster stability was found to increase sequentially from Cu₂₈-PPh₂Py to Cu₂₉-P(Ph-Cl)₃ and then to Cu₂₉-P(Ph-Me)₃, which indicates that stability is affected by the overall structure of the cluster. Structural adjustments to the metal core, shell, and core-shell bonding model, in moving from Cu₂₈-PPh₂Py to Cu₂₉-P(Ph-Cl)₃ and then to Cu₂₉-P(Ph-Me)₃, enable the structural evolution and mechanism responsible for their physicochemical properties to be understood and provide valuable insight into the structures of surface vacancies in copper nanoclusters and structure-property relationships.

Fabricating sub-nanometer materials through cluster assembly

The self-assembly of clusters provides a feasible approach for the bottom-up fabrication of functional materials with tailored properties. Sub-nanometer cluster assembly with a well-defined construction presents a precisely controllable structure and extraordinary properties, which provides an ideal model for the investigation of structures and properties at the molecular level. Non-covalent interactions between clusters may dominate the assembly behavior, appearing as tunable structures different from their nano-counterparts. Interactions between clusters and their superatom orbitals can significantly influence the electronic structures, because of which exceptional properties may emerge. In this paper, recent progress on cluster-based assemblies is introduced, including sub-nanometer building blocks of noble metal and polyoxometalate (POM) clusters. The structures, formation mechanism and properties of these cluster assemblies are discussed from experimental and theoretical aspects. This perspective aims to provide a new insight into the design and manufacture of sub-nanometer materials based on clusters.

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.

Nanocluster Transformation Induced by SbF6- Anions toward Boosting Photochemical Activities

The interactions between SbF₆^- and metal nanoclusters are of significance for customizing clusters from both structure and property aspects; however, the whole-segment monitoring of this customization remains challenging. In this work, by controlling the amount of introduced SbF₆^- anions, the step-by-step nanocluster evolutions from [Pt₁Ag₂₈(S-Adm)₁₈(PPh₃)₄]Cl₂ (Pt₁Ag₂₈-Cl) to [Pt₁Ag₂₈(S-Adm)₁₈(PPh₃)₄](SbF₆)₂ (Pt₁Ag₂₈-SbF₆) and then to [Pt₁Ag₃₀Cl₁(S-Adm)₁₈(PPh₃)₃](SbF₆)₃ (Pt₁Ag₃₀-SbF₆) have been mapped out with X-ray crystallography, with which atomic-level SbF₆^- counterion effects in reconstructing and rearranging nanoclusters are determined. The structure-dependent optical properties, including optical absorption, photoluminescence, and electrochemiluminescence (ECL), of these nanoclusters are then explored. Notably, the Pt₁Ag₃₀-SbF₆ nanocluster was ultrabright with a high phosphorescence quantum yield of 85% in N₂-purged solutions, while Pt₁Ag₂₈ nanoclusters were fluorescent with weaker emission intensities. Furthermore, Pt₁Ag₃₀-SbF₆ displayed superior ECL efficiency over Pt₁Ag₂₈-SbF₆, which was rationalized by its increased effectively exposed reactive facets. Both Pt₁Ag₃₀-SbF₆ and Pt₁Ag₂₈-SbF₆ demonstrated unprecedented high absolute ECL quantum efficiencies at sub-micromolar concentrations. This work is of great significance for revealing the SbF₆^- counterion effects on the control of both structures and luminescent properties.

Template-assisted alloying of atom-precise silver nanoclusters: a new approach to generate cluster functionality

To acquire the atomic design of new functional Ag(i) nanoclusters (NCs), a new synthetic approach of site-specific alloying has been unveiled, by which the neutral CO2 templated Ag20 core is confined through Cu containing two peripheral motif units. The impact of surface charge, size and shape of the template on the self-assembly of Ag(i) has been precisely controlled here for the first time and as a result, a similar pentagonal gyrobicupola-like Ag20 core is formed while varying the templates (S2-, CO3 2- and CO2). However, the surface charge generated on the Ag(i) core due to the presence of a neutral template opens up the possibility of this novel alloying process. The introduction of strongly interacted peripheral motif units (DMA-CuS-) on the Ag20 core enforces more rigidity in the skeleton that reduces the probability of non-radiative transition in the excited state by lowering the intramolecular vibration. In addition to this, the incorporation of electron-donating peripheral motif units modulates the frontier molecular arrangement that helps in attaining the synergy which would ultimately turn on the room-temperature emission properties. The electron-donating effect of the peripheral motif units further leads to a sharp reduction of the bandgap and the symmetric position of the heterometal in the cluster minimizes the intercluster distances which further influences the intercluster charge carrier transport. So, the precise structure-property correlation with this novel synthetic approach will pave the way for a well-functioning NC design.

Metal Cluster Triggered-Assembling Heterogeneous Au-Ag Nanoclusters with Highly Loading Performance and Biocompatible Capability

In this work, we firstly report the preparation of heterogeneously assembled structures Au-Ag nanoclusters (NCs) as good drug carriers with high loading performance and biocompatible capability. As glutathione-protected Au and Ag clusters self-assembled into porous Au-Ag NCs, the size value is about 1.358 (±0.05) nm. The morphology characterization revealed that the diameter of Au-Ag NCs is approximately 120 nm, as well as the corresponding potential ability in loading performance of the metal cluster triggered-assembling process. Compared with individual components, the stability and loading performance of heterogeneous Au-Ag NCs were improved and exhibit that the relative biocompatibility was enhanced. The exact information about this is that cell viability was approximately to 98% when cells were incubated with 100 µg mL−1 particle solution for 3 days. The drug release of Adriamycin from Au-Ag NCs was carried out in PBS at pH = 7.4 and 5.8, respectively. By simulating in vivo and tumor microenvironment, the release efficiency could reach over 65% at pH = 5.8 but less than 30% at pH = 7.2. Using an ultrasound field as external environment can accelerate the assembling process while metal clusters triggered assembling Au-Ag NCs. The size and morphology of the assembled Au-Ag NCs can be controlled by using different power parameters (8 W, 13 W, 18 W) under ambient atmosphere. Overall, a novel approach is exhibited, which conveys assembling work for metal clusters triggers into heterogeneous structures with porous characteristic. Its existing properties such as water-solubility, stability, low toxicity and capsulation can be considered as dependable agents in various biomedical applications and drug carriers in immunotherapies.

Versatile Superatom Complex Nanocluster for the Construction of Framework Materials

Accurately controlling the assembly of nanometer-sized building blocks presents an important but significant challenge for the construction of functional framework materials, which requires the development of highly stable versatile nanosized assembly modules with multiple coordination sites. In this study, [Ag₂₃(SAdm)₁₂]³⁺ (Ag₂₃, in which SAdm = 1-adamantanethiol, i.e., C₁₀H₁₅S), a chiral superatom complex nanocluster, was synthesized and assembled into various topologies. We constructed two kinds of framework materials, i.e., superatom complex inorganic framework (SCIF) and superatom complex organic framework (SCOF) materials, including [Ag₂₃(SAdm)₁₂](SbF₆)₂X (Ag₂₃-1; X = Cl^-/SbF₆^-, a SCIF), [Ag₂₃(SAdm)₁₂](SbF₆)₃ (Ag₂₃-2, a SCIF), [Ag₂₃(SAdm)₁₂](SbF₆)₃(bpy)₃ (Ag₂₃-bpy, a SCOF, in which bpy = 4,4'-bipyridine, i.e., C₁₀H₈N₂), and [Ag₂₃(SAdm)₁₂](SbF₆)₃(dpbz)₃ (Ag₂₃-dpbz, a SCOF, in which dpbz = 1,4-bis(4-pyridyl)benzene, i.e., C₁₆H₁₂N₂), owing to strong interactions between the versatile Ag₂₃ and the inorganic and organic linkers. Ag₂₃-1, Ag₂₃-2, and Ag₂₃-bpy exhibit two superstructures with interpenetrating frameworks and adamantane-like, hexagonal, and cubic topologies, while Ag₂₃-dpbz displays three superstructures with interpenetrating frameworks and cubic topologies. Ag₂₃-dpbz exhibits the largest specific surface area as well as the strongest photoluminescence and electrochemiluminescence signals owing to its dense network arrangement. This work contributes to the construction of nanocluster-based framework materials and helps to elucidate the effect of the assembly mode on the material properties and functionalities.

Polydopamine at biological interfaces

In the last years coating of surfaces in the presence of dopamine or other catecholamines in oxidative conditions to yield "polydopamine" films has become a popular, easy and versatile coating methodology. Polydopamine(s) offer(s) also a rich chemistry allowing to post-functionalize the obtained coatings with metal nanoparticles with polymers and proteins. However, the interactions either of covalent or non-covalent nature between polydopamine and biomolecules has only been explored more recently. They allow polydopamine to become a material, in the form of nanoparticles, membranes and other assemblies, in its own right not just as a coating. It is the aim of this review to describe the most recent advances in the design of composites between polydopamine and related eumelanin like materials with biomolecules like proteins, nucleotides, oligosaccharides and lipid assemblies. Furthermore, the interactions between polydopamine and living cells will be also reported.

Luminescent Sensors Based on the Assembly of Coinage Metal Nanoclusters

Coinage metals, such as Cu, Ag and Au, can form nanoclusters, which, when functionalized with ligands, have unique electronic and optical properties and are widely used in biomedical imaging, remote sensing, labeling, catalytic, etc. The mechanisms, structures and properties of nanocluster assemblies have been well reviewed. However, the collections and analyses of nanocluster assemblies for sensor application are few. This review examines different nanocluster sensor platforms with a focus on the assembly and analysis of the assembly processes and examples of applications.

Dual-emission fluorescent nanoprobe based on Ag nanoclusters for sensitive detection of Cu(II)

Noble metal nanoclusters have attracted much attention because of their excellent fluorescence properties. In this work, we demonstrated a dual-emission fluorescent nanocomposite based on silver nanoclusters. First, we synthesized positively charged His-AgNCs, which emits intense blue light, and then Ag nanoclusters with stable red emission were synthesized using DHLA as the ligand. Thus a dual-emission fluorescent nanoprobe was successfully obtained through electrostatic self-assembly, with the advantages of good water solubility and excellent stability. Based on the intensity ratio of the two emission peaks, the nanoprobe can be used for selective and sensitive detection of copper ions, and presents a good linear relationship within a certain concentration range. In addition, we also designed a polymer film, and our dual-emission nanoprobe was successfully loaded onto it, which means that the visual detection of copper ions is possible. This indicates that our dual-emission fluorescent nanoprobe has potential application prospects in environmental analysis, medical diagnosis, biological detection, etc.

Insight into the Mechanism of Single-Metal-Atom Tailoring on the Surface of Au-Cu Alloy Nanoclusters

Tailoring the surface structure of nanomaterials is desirable for investigating their mechanisms and properties from a nanochemistry perspective. The modification of the surface of metal nanoparticles with a single metal atom has proven difficult, which has hindered the understanding of the contribution of different motifs in nanoclusters to their properties. Herein, we report single-metal-atom surface tailoring by thermally etching the nanocluster Au_xCu_15-x(DPPMH)₃(SPhCl₂)₉ (x = 8 or 9) to obtain Au_xCu_16-x(DPPMH)₂(DPPM)(SPhCl₂)₉ (x = 9 or 10) nanoclusters. An Au₇Cu₄ core was observed in both nanoclusters, which can be regarded as part of an icosahedron. Experiments and theoretical simulations revealed the tailoring processes of the icosahedron. Both nanoclusters displayed an NIR-II emission, and the introduction of the surface metal atom led to a red-shift in the emission band from 983 to 1025 nm. This work contributes to the development of precisely tailored nanocluster structures and provides an understanding of structure-property correlations.

Site-specific doping of silver atoms into a Au25 nanocluster as directed by ligand binding preferences

For the first time site-specific doping of silver into a spherical Au25 nanocluster has been achieved in [Au19Ag6(MeOPhS)17(PPh3)6] (BF4)2 (Au19Ag6) through a dual-ligand coordination strategy. Single crystal X-ray structural analysis shows that the cluster has a distorted centered icosahedral Au@Au6Ag6 core of D 3 symmetry, in contrast to the I h Au@Au12 kernel in the well-known [Au25(SR)18]- (R = CH2CH2Ph). An interesting feature is the coexistence of [Au2(SPhOMe)3] dimeric staples and [P-Au-SPhOMe] semi-staples in the title cluster, due to the incorporation of PPh3. The observation of only one double-charged peak in ESI-TOF-MS confirms the ordered doping of silver atoms. Au19Ag6 is a 6e system showing a distinct absorption spectrum from [Au25(SR)18]-, that is, the HOMO-LUMO transition of Au19Ag6 is optically forbidden due to the P character of the superatomic frontier orbitals.

Self-Assembled Metal Nanoclusters: Driving Forces and Structural Correlation with Optical Properties

Studies on self-assembly of metal nanoclusters (MNCs) are an emerging field of research owing to their significant optical properties and potential applications in many areas. Fabricating the desired self-assembly structure for specific implementation has always been challenging in nanotechnology. The building blocks organize themselves into a hierarchical structure with a high order of directional control in the self-assembly process. An overview of the recent achievements in the self-assembly chemistry of MNCs is summarized in this review article. Here, we investigate the underlying mechanism for the self-assembly structures, and analysis reveals that van der Waals forces, electrostatic interaction, metallophilic interaction, and amphiphilicity are the crucial parameters. In addition, we discuss the principles of template-mediated interaction and the effect of external stimuli on assembly formation in detail. We also focus on the structural correlation of the assemblies with their photophysical properties. A deep perception of the self-assembly mechanism and the degree of interactions on the excited state dynamics is provided for the future synthesis of customizable MNCs with promising applications.