Controlling ultrasmall gold nanoparticles with atomic precision

Electrosynthesis of Atomically Precise Au Nanoclusters

Innovation in synthesis methodologies is crucial for advancing the discovery of new materials. This work reports the electrosynthesis of a [Au13(4-tBuPhC≡C)2(Dppe)5]Cl3 nanocluster (Au13 NC) protected by alkynyl and phosphine ligands. From simple precursor, HAuCl4 and ligands, the whole synthesis is driven by a constant potential in single electrolytic cell. X-ray crystallography determines its total structure. Control experiments, cyclic voltammetry, Proton Nuclear Magnetic Resonance (1H NMR), gas chromatography, and other characterizations demonstrate that a critical tetranuclear Au(I) complex defines the electrochemical redox behavior of the reaction solution. The critical role of a base (e.g., triethylamine) is to suppress the hydrogen evolution reaction at the cathode, paving the way for the reduction of Au ions. To resolve the problem of over-reduction and deposition of Au on the cathode, pulsed electrolysis, which is specific to electrosynthesis is employed. It significantly improves the reaction rate and the isolated yield of Au13. To extend the application scope, another four NCs protected by different ligands, [Au13(4-FPhC≡C)2(Dppe)5]Cl3, [Au8(2-CF3PhC≡C)2(Dppp)4](PF6)2, [Au11(Dppp)5]Cl3, and [Au8(SC2H4Ph)2(Dppp)4]Cl2 are synthesized electrochemically, demonstrating the versatility of the strategy.

N-Heterocyclic Carbene-Based Copolymers for Templated Synthesis and Stabilization of Gold Nanoparticles

Surface functionalization and colloidal stability are pivotal for numerous applications of gold nanoparticles (Au-NPs). Over the past decade, N-heterocyclic carbenes (NHCs) have emerged as promising ligands for stabilizing Au-NPs owing to their ease of synthesis, structural diversity, and strong metal-ligand bonds. Here, we introduce new Au(I)-NHCcopolymer scaffolds as precursors to multidentate NHC-protected Au-NPs. Ring-opening metathesis copolymerization of a norbornene-appended Au(I)-NHC complex with another functionalized norbornene comonomer provides NHC-Au(I) copolymers with modular compositions and structures. Upon reduction, these copolymers yield multidentate polyNHC-coated Au-NPs with varied properties and corona functionalities dictated by the secondary monomer. These nanoparticles exhibit excellent size homogeneity and stability against aggregation in various buffers, cell culture media, and under exposure to electrolytes, oxidants, and exogenous thiols over extended periods. Moreover, we demonstrate post-synthetic surface functionalization reactions of polyNHC-Au-NPs while maintaining colloidal stability, highlighting their robustness and potential for applications such as bioconjugation. Overall, these findings underscore the potential of ROMP-derived NHC-containing copolymers as highly tunable and versatile multidentate ligands that may be suitable for other inorganic colloids and flat surfaces.

Halide-Directed Ligand Engineering Enables Expedient, Controlled and Divergent Syntheses of Diphosphine-Protected Au Nanoclusters

Despite substantial progress in ligand engineering, the efforts in the field of Au nanoclusters have been concentrated almost exclusively on organic ligands. Halides, the most typical auxiliary inorganic ligands widely present in Au clusters, remain virtually unexplored, particularly regarding their effects on cluster construction. Herein, diphosphine Ph2P(CH2)nPPh2 (Ln, n = 1-6) is chosen as the co-protecting organic ligands and a comparative analysis on the influential roles of halide ions (Cl-, Br-, I-) in guiding Au cluster synthesis is conducted. A simple yet efficient halide-directed synthetic approach has been developed and a series of Au nanoclusters, including the known [Au18(L1)6Br4]2+, [Au13(L2)5Cl2]3+ and [Au8(L3)4Cl2]2+ that however crystallized in new polymorphic forms, as well as the new reduction-active [Au18(L1)6Cl4]2+, luminescence-enhanced [Au14(L3)5Br4]2+ and core-isomeric [Au11(Ln)4X2]+ (n = 4-6; X = Cl, Br, I), are obtained in a more expedient and controllable manner. This work clearly demonstrates the non-negligible roles of halide ions in directing cluster synthesis, and provides an easier access to diverse diphosphine-protected Au nanoclusters. This approach, promising in gram-scale synthesis, is expected to further extend the ligand scope and holds promise for advancing the diversified syntheses of a broader range of ligand-protected metal nanoclusters.

Applications of Au25 Nanoclusters in Photon-Based Cancer Therapies

Atomically precise gold nanoclusters (AuNCs) exhibit unique physical and optical properties, making them highly promising for targeted cancer therapy. Their small size enhances cellular uptake, facilitates rapid distribution to tumor tissues, and minimizes accumulation in non-target organs compared to larger gold nanoparticles. AuNCs, particularly Au25, show significant potential in phototherapy, including photothermal (PTT), photodynamic (PDT), and radiation therapies. These therapies benefit with minimal damage to surrounding healthy tissue. AuNCs also demonstrate excellent stability and biocompatibility, crucial for their effective use in clinical applications. Recent advances in the synthesis and functionalization of AuNCs have further improved their therapeutic efficacy, making them versatile agents for enhancing cancer treatment outcomes. Ongoing research aims to better understand their pharmacokinetics, biodistribution, and long-term safety, paving the way for their broader application in advanced cancer therapies.

Molecular tags for electron cryo-tomography

Electron cryotomography enables the direct visualisation of biological specimens without stains or fixation, revealing complex molecular landscapes at high resolution. However, identifying specific proteins within these crowded environments is challenging. Molecular tagging offers a promising solution by attaching visually distinctive markers to proteins of interest, differentiating them from the background. This review explores available tagging strategies, including gold nanoparticles, metal-binding proteins, nucleic acid nanostructures and protein-based tags. The identification and targeting strategies for each approach are discussed, highlighting their respective advantages and limitations. Future directions for advancing these tagging techniques to expand their applicability to broader research questions are also considered.

Selective synthesis of fluorescent metal nanoclusters over metal nanoparticles

Metal nanoparticles and nanoclusters are pivotal in nanomaterial science, each offering unique properties for diverse applications. Nanoclusters, typically smaller than 2 nm, exhibit distinct optical and electronic characteristics due to quantum confinement, resulting in fluorescence emission. In contrast, metal nanoparticles, sized between 2 and 100 nm, exhibit absorption spectra. Both are synthesized by reducing metal precursors in the presence of a suitable stabilizing agent. While nanoparticles have been the historical research focus, recent attention has shifted to nanoclusters for their exceptional properties and their synthesis has evolved significantly over the past few decades. This review discusses the selective synthesis of nanoclusters over nanoparticles, emphasizing the role of various factors such as ligand concentration (metal-to-ligand ratio), reducing agents, pH, reaction time and temperature, solvents, and assistant reagents. Higher ligand concentrations stabilize smaller nanoclusters by preventing aggregation, while lower concentrations lead to larger nanoparticles. Stronger reducing agents produce smaller, more uniform particles, whereas weaker reducing agents yield larger ones. pH affects nanocluster size and emission properties. Solvents and assistant reagents influence reaction kinetics and material properties. Temperature and reaction time also play critical roles in controlling nanocluster size and properties. These insights guide the optimized synthesis of metal nanoclusters, for their specific applications.

Raising Near-Infrared Photoluminescence Quantum Yield of Au42 Quantum Rod to 50% in Solutions and 75% in Films

Highly emissive gold nanoclusters (NCs) in the near-infrared (NIR) region are of wide interest, but challenges arise from the excessive nonradiative dissipation. Here, we demonstrate an effective suppression of the motions of surface motifs on the Au42(PET)32 rod (PET = 2-phenylethanethiolate) by noncoordinative interactions with amide molecules and accordingly raise the NIR emission (875/1045 nm peaks) quantum yield (QY) from 18% to 50% in deaerated solution at room temperature, which is rare in Au NCs. Cryogenic photoluminescence measurements indicate that amide molecules effectively suppress the vibrations associated with the Au-S staple motifs on Au42 and also enhance the radiative relaxation, both of which lead to stronger emission. When Au42 NCs are embedded in a polystyrene film containing amide molecules, the PLQY is further boosted to 75%. This research not only produces a highly emissive material but also provides crucial insights for the rational design of NIR emitters and advances the potential of atomically precise Au NCs for diverse applications.

Atomically Precise Nanometer-Sized Pt Catalysts with an Additional Photothermy Functionality

Atomically precise ~1-nm Pt nanoparticles (nanoclusters, NCs) with ambient stability are important in fundamental research and exhibit diverse practical applications (catalysis, biomedicine, etc.). However, synthesizing such materials is challenging. Herein, by employing the mixture ligand protecting strategy, we successfully synthesized the largest organic-ligand-protected (~1-nm) Pt23 NCs precisely characterized with mass spectrometry and single-crystal X-ray diffraction analyses. Interestingly, natural population analysis and Bader charge calculation indicate an alternate, varying charge -layer distribution in the sandwich-like Pt23 NC kernel. Pt23 NCs can catalyze the oxygen reduction reaction under acidic conditions without requiring calcination and other treatments, and the resulting specific and mass activities without further treatment are sevenfold and eightfold higher than those observed for commercial Pt/C catalysts, respectively. Density functional theory and d-band center calculations interpret the high activity. Furthermore, Pt23 NCs exhibit a photothermal conversion efficiency of 68.4 % under 532-nm laser irradiation and can be used at least for six cycles, thus demonstrating great potential for practical applications.

Visible to NIR-II Photoluminescence of Atomically Precise Gold Nanoclusters

Atomically precise gold nanoclusters (NCs) have emerged as a new class of precision materials and attracted wide interest in recent years. One of the unique properties of such nanoclusters pertains to their photoluminescence (PL), for it can widely span visible to near-infrared-I and -II wavelengths (NIR-I/II), and even beyond 1700 nm by manipulating the size, structure, and composition. The current research efforts focus on the structure-PL correlation and the development of strategies for raising the PL quantum yields, which is nontrivial when moving from the visible to the near-infrared wavelengths, especially in the NIR-II regions. This review summarizes the recent progress in the field, including i) the types of PL observed in gold NCs such as fluorescence, phosphorescence, and thermally activated delayed fluorescence, as well as dual emission; ii) some effective strategies that are devised to improve the PL quantum yield (QY) of gold NCs, such as heterometal doping, surface rigidification, and core phonon engineering, with double-digit QYs for the NIR PL on the horizons; and iii) the applications of luminescent gold NCs in bioimaging, photosensitization, and optoelectronics. Finally, the remaining challenges and opportunities for future research are highlighted.

Glutathione S-transferase templated copper nanoclusters as a fluorescent probe for turn-on sensing of chlorotetracycline

Hereby, facile-green copper nanoclusters templated by glutathione S-transferase (GST-CuNCs) have been innovatively synthesized via a simple one-pot stirring method at room temperature. The as-prepared nanoclusters exhibited uniform size with satisfactory fluorescence intensity, good stability and low cytotoxicity. Significantly, the fluorescence of the obtained GST-CuNCs could be considerably enhanced by the addition of chlorotetracycline (CTC) rather than other analogues of CTC, which was ascribed to the aggregation-induced enhancement caused by the interaction between CTC and GST. The enhanced fluorescence intensity demonstrated a good linear correlation with the CTC concentration in the range of 30-120 μM (R2 = 0.99517), and the low detection limit was 69.7 nM. Furthermore, the proposed approach showed favorable selectivity and anti-interference toward CTC among prevalent ions and amino acids. Additionally, this nanoprobe was also applied to the quantitative detection of CTC in serum samples with satisfactory outcomes, which demonstrated excellent prospects for practical applications.

Tuneable Plasmonic Resonances Of A Dynamic Thin Film Of Ultrasmall Nanocrystals Modified In the Anti-Galvanic Reduction Process

Ultrasmall gold nanoparticles (NPs) have revolutionized nanotechnology as they are an excellent starting substrate for the synthesis of organic-inorganic hybrid materials with photonic or energy conversion applications, often with a responsive nature. However, ultrasmall NPs do not sustain plasmonic resonances, preventing their use in plasmon-related applications. In the presented work, we show a method of chemical modification of ultrasmall gold nanoparticles in order to fabricate dynamically controlled plasmonic thin films. For this purpose, we used the Anti-Galvanic Reduction process (AGR) to modify the surface of small gold nanoparticles, inducing plasmonic properties without notable size increases. Au@Ag NPs are then modified with liquid crystal-like organic ligands. The obtained NPs can assemble into densely packed films with long-range order and temperature-dependent structural properties. Namely, we detect two, fully reversible phase transitions between the hexagonal and cubic symmetries. The combination of AGR and organic surface modifications enabled us to demonstrate the possibility of managing plasmonic properties in the thin film of ~2 nm diameter metallic NPs.

Biological Interaction and Imaging of Ultrasmall Gold Nanoparticles

The ultrasmall gold nanoparticles (AuNPs), serving as a bridge between small molecules and traditional inorganic nanoparticles, create significant opportunities to address many challenges in the health field. This review discusses the recent advances in the biological interactions and imaging of ultrasmall AuNPs. The challenges and the future development directions of the ultrasmall AuNPs are presented.

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.

Sandwich-Kernelled AgCu Nanoclusters with Golden Ratio Geometry and Promising Photothermal Efficiency

Metal nanoclusters have recently attracted extensive interest from the scientific community. However, unlike carbon-based materials and metal nanocrystals, they rarely exhibit a sheet kernel structure, probably owing to the instability caused by the high exposure of metal atoms (particularly in the relatively less noble Ag or Cu nanoclusters) in such a structure. Herein, we synthesized a novel AgCu nanocluster with a sandwich-like kernel (diameter≈0.9 nm and length≈0.25 nm) by introducing the furfuryl mercaptan ligand (FUR) and the alloying strategy. Interestingly, the kernel consists of a centered silver atom and two planar Ag10 pentacle units with completely mirrored symmetry after a rotation of 36 degrees. The two Ag10 pentacles and some extended structures show an unreported golden ratio geometry, and the two inner five-membered rings and the centered Ag atom form an unanticipated full-metal ferrocene-like structure. The featured kernel structure causes the dominant radial direction transition of excitation electrons, as determined via time-dependent density functional theory calculations, which affords the protruding absorption at 612 nm and contributes to the promising photothermal conversion efficiency of 67.6 % of the as-obtained nanocluster, having important implications for structure-property correlation and the development of nanocluser-based photothermal materials.

Preorganized Nitrogen Sites for Au11 Amidation: A Generalizable Strategy toward Precision Functionalization of Metal Nanoclusters

Atomically precise metal nanoclusters have received tremendous attention due to their unique structures and properties. Although synthetic approaches to this kind of nanomaterial have been well developed, methods toward precision functionalization of the as-synthesized metal nanoclusters are extremely limited, hindering their interfacial modification and related performance improvement. Herein, an amidation strategy has been developed for the precision functionalization of the Au₁₁ nanocluster based on preorganized nitrogen sites. The nanocluster amidation did not change the number of gold atoms in the Au₁₁ kernel and their bonding mode to the surface ligands but slightly modified the arrangement of gold atoms with the introduction of functionality and chirality, thus representing a relatively mild method for the modification of metal nanoclusters. The stability and oxidation barrier of the Au₁₁ nanocluster are also improved accordingly. The method developed here would be a generalizable strategy for the precision functionalization of metal nanoclusters.

Nanoclusterzyme for Dual Colorimetric Sensings: A Case Study on [Au14 (Dppp)5 I4 ]2

The enzymatic activity of atomically precise metal nanoclusters has recently been recognized; however, the number of nanoclusterzymes is very small. Besides, the applications of nanoclusterzyme wait to be explored. Herein, a novel nanoclusterzyme is synthesized and its structure is majorly resolved by single-crystal X-ray diffraction and mass spectrometry, which reveal that the nanocluster consists of an Au₁₃ icosahedron capped by an exterior shell including four I, three Dppp (1,3-bis(diphenylphosphino) propane) ligands, and a rarely reported Dppp-Au-Dppp handle staple, which contributes a lot to the enzyme activity of [Au₁₄ (Dppp)₅ I₄ ]²⁺ nanocluster. The as-obtained nanocluster can catalyze oxygen to O₂ ^•- under visible light irradiation with a specific activity up to 0.182 U·mg^-1 and lead to the blue color of 3,3',5,5'-tetramethylbenzidine (TMB) in both solution and solid states. With the addition of acetylcholinesterase (AChE), the blue color of (Au₁₄  + TMB) solution system disappears due to the nanoclusterzyme activity inhibition, but the further addition of organophosphorus pesticides (OPs) into the above mixture can restore the nanoclusterzyme and recover the blue color. Based on the color turn-off and on, the various nanoclusterzyme-containing systems are used to colorimetrically sense AChE and OPs with the detection limits reaching 0.04 mU·mL^-1 and 0.02 ng·mL^-1 , respectively.

Regulating the Electronic Structure of Metal Nanoclusters by Longitudinal Single-Dithiolate Substitution

It is significant but challenging to understand the property evolution of metal nanoclusters by orientated regulation of the electronic structure. Previous research has demonstrated that the optical properties of metal nanoclusters with anisotropic structures are greatly impacted by their longitudinal electronic structure. However, the manipulation of optical properties of metal nanoclusters by regulating their electronic structure through longitudinal dithiolate substitutions has not yet been reported. In this study, we first achieved the longitudinal single-dithiolate replacement of metal nanoclusters and obtained two novel nanoclusters: Au₂₈(SPh-^tBu)₁₈(SCH₂SCH₂S) and Au₂₈(SPh-^tBu)₁₈(SCH₂CH₂CH₂S). Both experimental and theoretical results demonstrated the regulation of the electronic structure (dipole moment) in the z (longitudinal) and x directions, resulting in absorption redshift and photoluminescence (polarity) enhancement. These findings not only deepen the understanding of the property-electronic structure correlation of metal nanoclusters but also provide guidance for their subtle property tuning.

Synthesis and luminescence monitoring of iridium(III) complex-functionalized gold nanoparticles and their application for determination of gold(III) ions

A new method is presented for the one-step synthesis and real-time monitoring of iridium(III) complex-functionalized AuNPs from the precursor gold(III) chloride (AuCl₃). The functionalized AuNPs with an average size of 8 - 20 nm were obtained by the reduction of Au³⁺ ions by the alkyne group of iridium(III) complexes, which was accompanied by the anchoring iridium(III) complexes on the surface of the nanoparticles. Meanwhile, the luminescence of the iridium(III) complexes was effectively quenched due to distance-dependent fluorescence quenching by AuNPs, thereby enabling luminescence monitoring of the formation process of the functionalized AuNPs and obtaining scattering information and spectral information in real time. Moreover, this method was applied to the determination of Au³⁺ ions in buffer with a limit of detection of 0.38 μM at 700 nm in luminescence mode, while the detection limit for absorbance was 10.04 μM. Importantly, the multimodal detection strategy alleviates interference from other metal ions. Furthermore, the iridium(III) alkyne complexes were capable of imaging mitochondrial Au³⁺ ions in living cells. Taken together, this work opens a new avenue for convenient synthesis and monitoring formation of functionalized AuNPs, and also provides a tool for selective determination of Au³⁺ ions in solution and in cellulo.

Effect of total charge on the electronic structure of thiolate-protected X@Ag12 superatoms (X = Ag, Au)

Electronic structures of chemically synthesized silver-based clusters [XAg₁₆(TBBT)₁₂]^3- (X = Ag or Au; TBBT = 4-tert-butylbenzenethiolate) having an icosahedral X@Ag₁₂ superatomic core were studied by gas-phase photoelectron spectroscopy and density functional theory calculations. The electron binding energy of the highest occupied molecular orbital (HOMO) with a 1P superatomic nature was determined to be 0.23 and 0.29 eV for X = Ag or Au, respectively. Resonant tunnelling electron emission through the repulsive Coulomb barrier (RCB) was observed. From the kinetic energy of the tunnelling electrons, it was estimated that the lowest unoccupied molecular orbital (LUMO) was supported at 1.51 and 1.62 eV above the vacuum level by the RCB for X = Ag or Au, respectively. The HOMO of [XAg₁₆(TBBT)₁₂]^3- (X = Ag or Au) was destabilized by 3.74 and 3.71 eV, respectively, compared with those of [XAg₂₄(DMBT)₁₈]^- (DMBT = 2,4-dimethylbenzenethiolate) having the icosahedral X@Ag₁₂ core due to the larger negative charge imparted by the ligand layers.

Cadmium-Doped and Pincer Ligand-Modified Gold Nanocluster for Catalytic KA2 Reaction

A gold nanocluster Au₁₇ Cd₂ (PNP)₂ (SR)₁₂ (PNP=2,6-bis(diphenylphosphinomethyl)pyridine, SR=4-MeOPhS) consisting of an icosahedral Au₁₃ kernel, two Au₂ CdS₆ staple motifs, and two PNP pincer ligands has been designed, synthesized and well characterized. This cadmium and PNP pincer ligand co-modified gold nanocluster showed high catalytic efficiency in the KA² reaction, featuring high TON, mild reaction conditions, broad substrate scope as well as catalyst recyclability. Comparison of the catalytic performance between Au₁₇ Cd₂ (PNP)₂ (SR)₁₂ and the structurally similar single cadmium (or PNP) modified gold nanoclusters demonstrates that the co-existence of the cadmium and PNP on the surface is crucial for the high catalytic activity of the gold nanocluster. This work would be enlightening for developing efficient catalysts for cascade reactions and discovering the catalytic potential of metal nanoclusters in organic transformations.

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.

Phosphinous Acid-Phosphinito Tetra-Icosahedral Au52 Nanoclusters for Electrocatalytic Oxygen Reduction

While the formation of superatomic nanoclusters by the three-dimensional assembly of icosahedral units was predicted in 1987, the synthesis and structural determination of such clusters have proven to be incredibly challenging. Herein, we employ a mixed-ligand strategy to prepare phosphinous acid-phosphinito gold nanocluster Au₅₂(HOPPh₂)₈(OPPh₂)₄(TBBT)₁₆ with a tetra-icosahedral kernel. Unlike expected, each icosahedral Au₁₃ unit shares one vertex gold atom with two adjacent units, resulting in a "puckered" ring shape with a nuclearity of 48 in the kernel. The phosphinous acid-phosphinito ligand set, which consists of two phosphinous acids and one phosphinito motif, has strong intramolecular hydrogen bonds; the π-π stacking interactions between the phosphorus- and sulfur-based ligands provide additional stabilization to the kernel. Highly stable Au₅₂(HOPPh₂)₈(OPPh₂)₄(TBBT)₁₆ serves as an effective electrocatalyst in the oxygen reduction reaction. Density functional theory calculations suggest that the phosphinous acid-phosphinito ligands provide the most active sites in the electrochemical catalysis, with O* formation being the rate-determining step.

Modulating luminescence and assembled shapes of ultrasmall Au nanoparticles towards hierarchical information encryption

Because of their intriguing luminescence performances, ultrasmall Au nanoparticles (AuNPs) and their assemblies hold great potential in diverse applications, including information security. However, modulating luminescence and assembled shapes of ultrasmall AuNPs to achieve a high-security level of stored information is an enduring and significant challenge. Herein, we report a facile strategy using Pluronic F127 as an adaptive template for preparing Au nanoassemblies (AuNAs) with controllable structures and tunable luminescence to realize hierarchical information encryption through modulating excitation light. The template guided ultrasmall AuNP in situ growth in the inner core and assembled these ultrasmall AuNPs into intriguing necklace-like or spherical nanoarchitectures. By regulating the type of ligand and reductant, their emission was also tunable, ranging from green to the second near-infrared (NIR-II) region. The excitation-dependent emission could be shifted from red to NIR-II, and this significant shift was considerably distinct from the small range variation of conventional nanomaterials in the visible region. In virtue of tunable luminescence and controllable structures, we expanded their potential utility to hierarchical information encryption, and the true information could be decrypted in a two-step sequential manner by regulating excitation light. These findings provided a novel pathway for creating uniform nanomaterials with desired functions for potential applications in information security.

Horizontal expansion of biicosahedral M13-based nanoclusters: resolving decades-long questions

For metal nanoclusters with the "cluster of clusters" intramolecular evolution pattern, most efforts have been made towards the vertical superposition of icosahedral nanobuilding blocks (e.g., from mono-icosahedral Au₁₃ to bi-icosahedral Au₂₅ and tri-icosahedral Au₃₇), while the horizontal expansion of these rod-shaped multi-icosahedral aggregates was largely neglected. We herein report the horizontal expansion of the biicosahedral M₂₅ cluster framework, yielding an [Au₁₉Ag₁₂(S-Adm)₆(DPPM)₆Cl₇]²⁺ nanocluster that contains an Au₁₃Ag₁₂ kernel and six Au₁(DPPM)₁(S-Adm)₁ peripheral wings. The structural determination of [Au₁₉Ag₁₂(S-Adm)₆(DPPM)₆Cl₇]²⁺ resolved a decades-long question towards rod-shaped multi-icosahedral aggregates: how to load bidentate phosphine and bulky thiol ligands onto the nanocluster framework? The structural comparison between [Au₁₉Ag₁₂(S-Adm)₆(DPPM)₆Cl₇]²⁺ and previously reported [Au₁₃Ag₁₂(PPh₃)₁₀Cl₈]²⁺ or [Au₁₃Ag₁₂(SR)₅(PPh₃)₁₀Cl₂]²⁺ rationalized the unique packing of Au₁(DPPM)₁(S-Adm)₁ motif structures on the surface of the former nanocluster. Overall, this work presents the horizontal expansion of rod-shaped multi-icosahedral nanoclusters, which provides new insights into the preparation of novel icosahedron-based aggregates with both vertically and horizontally growing extensions.

A novel fluorescent "OFF-ON" sensing strategy for Hg (II) in water based on functionalized gold nanoparticles

Mercury ion (Hg²⁺) is a heavy metal pollutant that can affect the safety of water environment and endanger human health. A novel detection strategy (GNPs-_L-Cys-Rh6G2) for Hg²⁺ based on a fluorescence "OFF-ON" was proposed. Gold nanoparticles (GNPs) were assembled with _l-cysteine (_L-Cys), which was used as a "bridge" to link with rhodamine 6G derivatives (Rh6G2). The fluorescence state transition of GNPs-_L-Cys-Rh6G2 switching from "OFF"-"ON" was observed because Hg²⁺ opened the spirolactam ring through a catalytic hydrolysis mechanism. The fluorescence signal of the GNPs-_L-Cys-Rh6G2 system mixed with Hg²⁺ in the concentration range of 10-100 μM was analyzed and determined with a limit of detection (LOD) of 2 μM (S/N = 3). Moreover, the spiked Hg²⁺ concentration in real water samples were successfully quantified by GNPs-_L-Cys-Rh6G2, which was in line with the ideal average recovery rate and relative standard deviation. The proposed strategy exhibited high specificity, sensitivity and stability, providing a novel sensing platform for heavy metal ions detection in water environment.

Preparation of Photoswitchable Polyacrylic Nanocomposite Fibers Containing Au Nanorods and Spiropyran: Optical and Plasmonic Properties

Photoswitchable nanofibers and nanocomposite fibers containing plasmonic nanoparticles have attracted a great deal of interest in optical and plasmonic devices. Herein, photoswitchable poly(methyl methacrylate-co-vinylimidazole-co-spiropyran ethyl acrylate) (MVSP) and its copolymer with butyl acrylate (MBVSP) were prepared via emulsion polymerization, and the corresponding nanofibers (MVSP@NF and MBVSP@NF) and nanocomposite fibers (MVSP/Au@NF and MBVSP/Au@NF) containing AuNRs were fabricated through electrospinning. FTIR and ¹H NMR analyses confirmed the progress of the copolymerization reaction. The morphology of the prepared nanofibers containing AuNRs with an aspect ratio of 2.5 was identified by SEM and TEM techniques. The inclusion of vinylimidazole into the copolymer chains resulted in well-dispersed AuNRs. Photoisomerization studies revealed a higher photochromic efficiency for MBVSP@F (reflective intensity of 37.4%) with respect to MVSP@NF (reflective intensity of 62.5%) because of the greater flexibility of the chains. In addition, the presence of AuNRs in the nanocomposite fibers with high absorptivity intensified the photochromic properties for both samples. The polarization-dependent plasmonic band of AuNRs was switched between 650 and 634 nm through the photoisomerization of nonpolar SP to polar MC reversibly for MVSP/Au@NF. This displacement was just 4 nm for MBVSP/Au@NF, owing to the limited coupling between AuNRs and MC isomers. Besides, the capability of both nanocomposite fibers for reversible optical patterning was investigated by fast write-erase cycles. Enhanced photofatigue resistance in those fibers and the photomodulation of the plasmonic band of AuNRs using SP to MC isomerization revealed their promising potential for optical patterning and on-demand real-time plasmonic devices.

Synthesis of silica-stabilized Ag44 clusters aided by a designed mercaptosilane ligand

The novel and precise design of both a microscopic ligand and macroscopic structure has been demonstrated to improve the stability and potential optical applications of Ag₄₄ clusters. The ligand with designed silane substituents on its thiophenol enabled the synthesized [Ag₄₄(SPhSi(OEt)₃)₃₀](PPh₄)₄ clusters to maintain UV-vis absorption for 13 h when heated at 60 °C in air and be readily coated with silica shells via a one-pot reverse microemulsion method. This composite structure overcomes the issue that non-luminescent Ag₄₄ clusters cannot be applied in photothermal and photoacoustic imaging due to their instability.

A theoretical study of the monolayer-protected gold cluster Au317(SR)110

Significant efforts have been made to uncover the structures of monolayer-protected gold nanoclusters. However, the synthesis, crystallization, and structural analysis of gold nanoclusters with over 300 metal atoms is a grand challenge. In this work, a new gold nanocluster containing 317 gold atoms and 110 thiolate (SH) ligands (referred to as Au₃₁₇(SH)₁₁₀) is theoretically studied, which is larger in size than the formerly reported Au₂₇₉(SR)₈₄ cluster. The stability of the Au₃₁₇(SH)₁₁₀ cluster is studied based on calculations of the averaged cluster formation energy (E_ave), indicating that Au₃₁₇(SH)₁₁₀ has good structural stability and that the SPhCOOH (p-MBA) ligand is a good candidate for stabilizing the cluster. The calculation of density of state and the time-dependent density functional theory (TD-DFT) calculations of the optical absorption properties show that Au₃₁₇(SH)₁₁₀ is in a metallic state.

Surface environment complication makes Ag29 nanoclusters more robust and leads to their unique packing in the supracrystal lattice

Silver nanoclusters have received unprecedented attention in cluster science owing to their promising functionalities and intriguing physical/chemical properties. However, essential instability significantly impedes their extensive applications. We herein propose a strategy termed “surface environment complication” to endow Ag₂₉ nanoclusters with high robustness. The Ag₂₉(S-Adm)₁₈(PPh₃)₄ nanocluster with monodentate PPh₃ ligands was extremely unstable and uncrystallizable. By substituting PPh₃ with bidentate PPh₂py with dual coordination sites (i.e., P and N), the Ag₂₉ cluster framework was twisted because of the generation of N–Ag interactions, and three NO₃ ligands were further anchored onto the nanocluster surface, yielding a new Ag₂₉(S-Adm)₁₅(NO₃)₃(PPh₂py)₄ nanocluster with high stability. The metal-control or ligand-control effects on stabilizing the Ag₂₉ nanocluster were further evaluated. Besides, Ag₂₉(S-Adm)₁₅(NO₃)₃(PPh₂py)₄ followed a unique packing mode in the supracrystal lattice with several intercluster channels, which has yet been observed in other M₂₉ cluster crystals. Overall, this work presents a new approach (i.e., surface environment complication) for tailoring the surface environment and improving the stability of metal nanoclusters.

A strategy of “surface environment complication” has been exploited to endow Ag₂₉ nanoclusters with high robustness and a unique packing mode in the supracrystal lattice.

Trinuclear anionic gold clusters bridged by dialkylsilylene and dialkylgermylene

While the chemistry of gold clusters has been developed rapidly, the knowledge of trinuclear gold clusters with low-valent gold remains scarce. Herein, we report the synthesis, structural characterization, and density...

Full-Color Tunable Circularly Polarized Luminescence Induced by the Crystal Defect from the Co-assembly of Chiral Silver(I) Clusters and Dyes

Four pairs of defective crystals exhibiting full-color emission and circularly polarized luminescence (CPL) with high luminescence dissymmetry factor (g_lum) values (∼3 × 10^-3) were successfully obtained by doping dye molecules into the chiral crystalline metal cluster-based matrixes. The dye molecules function as defect inducers and confer fluorescence on the crystals. Studies reveal that electrostatic interactions provide the main impetus in generating defective crystals, and the restricted effect of chiral space and the weak interactions in defect crystal enable the efficient chiral transfer from the intrinsically chiral host silver(I) clusters to achiral luminescent dopants and finally induce them to emit bright CPL. This defect engineering strategy opens a new way to versatile functions for crystalline cluster-based materials.

Spider Toxin Peptide-Induced NIR Gold Nanocluster Fabrication for GSH-Responsive Cancer Cell Imaging and Nuclei Translocation

Goldnanoclusters (GNCs) have become a promising nanomaterial for bioimaging because of their unique optical properties and biocompatibility. In this study, lycosin-I peptide, which possesses a highly selective anticancer activity by affecting the permeability of cancer cell membrane, was firstly modified for constructing fluorescent GNCs (LGNCs) for bioimaging of tumor cells. The obtained LGNCs exhibited strong near-infrared (NIR) fluorescence, which can be further enhanced by the peptide-induced aggregation and selectively stained three cancerous cell lines over normal cell lines with low intrinsic toxicity. After uptake by tumor cells, LGNC aggregates can be depolymerized into ultrasmall nanoclusters by high-level glutathione (GSH) and realize the nuclear targeting translocation. Collectively, our work suggests the potential of natural active biomolecules in designing NIR fluorescent GNCs for bioimaging.

On the Roles of Electron Transfer in Catalysis by Nanoclusters and Nanoparticles

Electron transfer plays a major role in chemical reactions and processes, and this is particularly true of catalysis by nanomaterials. The advent of metal nanoparticle (NP) catalysts, recently including atomically precise nanoclusters (NCs) as parts of nanocatalyst devices has brought increased control of the relationship between NP and NC structures and their catalytic functions. Consequently, the molecular definition of these new nanocatalysts has allowed a better understanding and management of various kinds of electron transfer involved in the catalytic processes. This Minireview brings a chemist's view of several major aspects of electron-transfer functions concerning NPs and NCs in catalytic processes. Particular focus concerns the role of NPs and NCs as electron reservoirs and light-induced antenna in catalytic processes from H₂ generation to more complex reactions and sustainable energy production.

Novel class of water-soluble phosphonate silver cluster assembled material for efficient photoelectric sensing and photoacoustic imaging

Owing to the atomic precession and exotic photophysical properties, silver cluster assembled materials (CAMs) have been explored for use as functional nanomaterials in recent years. Although a small number of thiolate protected silver CAMs have previously been investigated, the synthesis of thiol-free analogues and their solubility remain challenging. Here, the structure-property correlation of a newly synthesized one-dimensional phenyl phosphonate protected [Ag₂(PhPO₃H)₂(apy)₂], (in which, 4,4'-azopyridine = apy) CAM is demonstrated. The multifunctional surface protecting ligand is strategically attached to the core for the first time to tailor the solubility, structural stability and charge transfer mechanism. The small size of the cluster building blocks, along with the choice of organic linker molecules, efficiently stabilize the structure via intra-chain π-π stacking while inter-chains π-π interactions create a two-dimensional supramolecular architecture. The advantageous band structure associated with the charge transfer phenomenon and the high structural stability of the material are guided to explore the sustainable photoresponsive character of this CAM, resulting in the generation of an 82 nA photocurrent. Additionally, the unprecedented water solubility, which is very rare for this class of material, provides opportunities for use in biomedical imaging applications. The measured photoacoustic signal strength confirms the blood vessel mimicking capabilities of the portrayed material at a depth of approximately 3 mm inside chicken breast tissue.

[Ag71(S-tBu)31(Dppm)](SbF6)2: an intermediate-sized metalloid silver nanocluster containing a building block of Ag64

An intermediate-sized atomically precise metalloid silver nanocluster [Ag₇₁(SR)₃₁(Dppm)](SbF₆)₂ (Dppm = bis (diphenylphosphino)methane, SR = S-^tBu) is reported, which comprises one building block Ag₆₄, six SR₅ pentagons, one sole SR ligand, a DppmAg₂ handle, and an Ag₅ lid. Structurally, a decahedron Ag₂₃ kernel is observed in the metalloid silver nanocluster. Moreover, the Ag₆₄ unit provides insights into the growth of large clusters such as Ag₁₃₆(SR)₆₄Cl₃ and Ag₁₄₁(SR)₄₀Br₁₂via assembly. The observed decahedron Ag₂₃ provides a deeper understanding on Marks decahedron in larger nanoclusters, and the [Ag₇₁(S-^tBu)₃₁(Dppm)](SbF₆)₂ uses Ag₆₄ as a building block to predict the structure of larger metalloid nanoclusters.

Trinuclear cationic silver nanoclusters based-on bis-(phosphine) ligands and stabilized by CF3SO3− anions

Three trinuclear cationic silver nanoclusters based-on bis-(phosphine) ligands and stabilized by CF₃SO₃⁻ anions, displayed excellent photocurrent responses and electrochemical properties.