Three-Stage Evolution from Nonscalable to Scalable Optical Properties of Thiolate-Protected Gold Nanoclusters

Recent Advances in Understanding Triplet States in Metal Nanoclusters: Their Formation, Energy Transfer, and Applications in Photon Upconversion

Recent experimental findings, rapidly accumulating over the past few years, has revealed that in the electronic excited states of metal nanoclusters (MNCs) composed of noble metal atoms (e.g., Cu, Ag, or Au), triplet states are generated with remarkably high efficiency, exerting a pivotal influence over the photophysical properties of the MNCs, notably their photoluminescence characteristics. As a result, MNCs are increasingly recognized as promising luminescent nanomaterials that exhibit room-temperature phosphorescence and thermally activated delayed fluorescence. Furthermore, the significance of triplet-state-mediated energy transfer and charge transfer in intermolecular photophysical processes is gaining increasing recognition, particularly in the applications of MNCs as photosensitizers for singlet oxygen and organic molecular triplets. This Perspective focuses on recent advances in understanding of the formation and photophysics of triplet states in MNCs. Additionally, a brief overview is provided of a series of studies exploring the use of MNCs as triplet sensitizers for photon upconversion via triplet-triplet annihilation, and future prospects for this emerging application are discussed.

A comprehensive review of atomically precise metal nanoclusters with emergent photophysical properties towards diverse applications

Atomically precise metal nanoclusters (MNCs) composed of a few to hundreds of metal atoms represent an emerging class of nanomaterials with a precise composition. With the size approaching the Fermi wavelength of electrons, their energy levels are well-separated, leading to molecule-like properties, like discrete single electronic transitions, tunable photoluminescence (PL), inherent structural anisotropy, and distinct redox behavior. Extensive synthetic efforts and electronic structure revelation have expanded applicability of MNCs in catalysis, optoelectronics, and biology. This review highlights the intriguing photophysical and electrochemical behaviors of MNCs and their regulatory parameters and applications. Initially, we present a brief discussion on the evolution of MNCs from gas-phase naked metal clusters to monolayer ligand-protected MNCs along with representative studies on their electronic structure. Due to their quantized molecular orbitals, they often exhibit PL, which can be regulated based on their capping ligands, number of atoms, crystal packing, presence of heterometal, and surrounding environment. Apart from PL, the relaxation pathways of MNCs on an ultrafast time scale have been extensively studied, which significantly differ from that of plasmonic metal nanoparticles. Moreover, their interaction with high-intensity light results in unique non-linear optical properties. The synergy between MNCs in a hierarchical self-assembled structure has been exploited to enhance their PL by precisely tuning their non-covalent interactions. Moreover, several NC-based hybrids have been designed to exhibit efficient electron or energy transfer in the photoexcited state. In the next section, we briefly focus on the redox behavior of NCs and facile electron transfer to suitable substrates, which result in enzyme-like catalytic activity. Utilizing these photophysical and electrochemical behaviors, NCs are widely employed in catalysis, optical sensing, and light-harvesting applications, which are also discussed in this review. In the final section, conclusions and open questions for the NC research community are included. This review will provide a comprehensive view of the emerging physicochemical properties of MNCs, thereby enabling an understanding for their precise modulation in future.

Luminescent metal nanoclusters and their application in bioimaging

Owing to their unique optical properties and atomically precise structures, metal nanoclusters (MNCs) constitute a new generation of optical probe materials. This mini-review provides a brief overview of luminescence mechanisms and modulation methods of luminescent metal nanoclusters in recent years. Based on these photophysical phenomena, the applications of cluster-based optical probes in optical bioimaging and related sensing, disease diagnosis, and treatment are summarized. Some challenges are also listed at the end.

When Metal Nanoclusters Meet Smart Synthesis

Atomically precise metal nanoclusters (MNCs) represent a fascinating class of ultrasmall nanoparticles with molecule-like properties, bridging conventional metal-ligand complexes and nanocrystals. Despite their potential for various applications, synthesis challenges such as a precise understanding of varied synthetic parameters and property-driven synthesis persist, hindering their full exploitation and wider application. Incorporating smart synthesis methodologies, including a closed-loop framework of automation, data interpretation, and feedback from AI, offers promising solutions to address these challenges. In this perspective, we summarize the closed-loop smart synthesis that has been demonstrated in various nanomaterials and explore the research frontiers of smart synthesis for MNCs. Moreover, the perspectives on the inherent challenges and opportunities of smart synthesis for MNCs are discussed, aiming to provide insights and directions for future advancements in this emerging field of AI for Science, while the integration of deep learning algorithms stands to substantially enrich research in smart synthesis by offering enhanced predictive capabilities, optimization strategies, and control mechanisms, thereby extending the potential of MNC synthesis.

Octahedral vs Tiara-like Pd6(SR)12 Clusters

Atomically precise Pd-thiolate clusters are well-known for their well-defined structures and diverse applications involving catalysis, sensors, and biomedicine. While many of these clusters have been studied, their molecular structures typically feature a tiara-like arrangement. In this study, we present the first example of a non-tiara-like Pd-thiolate cluster: the octahedral Pd6(SC6H11)12 (denoted as Pd6-Oct). The composition and geometric structure of the cluster were characterized using electrospray ionization mass spectrometry (ESI-MS) together with single-crystal X-ray diffraction (SXRD). Despite having a similar chemical composition to tiara-like Pd6(SC2H4Ph)12 (denoted as Pd6-Tia), Pd6-Oct exhibits a distinctly different geometric structure. Additionally, UV-vis-NIR absorption spectroscopy combined with quantum chemical calculations provided valuable insights into the electronic structures of these clusters. The excited-state dynamics, host-guest chemistry, and the catalytic properties of Pd6-Oct and Pd6-Tia were examined to compare their structure-property relationships. This research represents significant advances in the synthesis and understanding of structure-property correlations in Pd-thiolate clusters.

Micro-Ring Morphology of Ag7NCs and Light-Induced Reversible Interconversion of FCC Ag14NCs via Cu2+ ions-Mediated Particle-Assisted Reversible Interconversion

Despite the remarkable progress made on intercluster conversion in atomically precise metal nanoclusters (MNCs) and their self-organization to develop microscopic molecular architecture with well-defined size and shape, achieving light-induced reversible structural transformation and the development of micro-ring self-assembly in MNCs have, so far, remained elusive. The present investigation touches on these two long-standing quests by showcasing a new route, light-induced Particle-Assisted Reversible Interconversion (PARI) for the reversible transformation from Face Centered Cubic (FCC) Ag14NCs to Ag7NCs. Our studies reveal that the lack of plasmonic silver nanoparticles (AgNPs) in the system results in the formation of Ag7NCs with metallic kernels having centrosymmetric crystal packing. The molecular self-organization of Ag7NCs through various non-covalent interactions such as C-H⋅⋅⋅O, C-H⋅⋅⋅H-C, and C-H⋅⋅⋅π leads to the formation of micro-ring morphology, a unique molecular architecture in MNCs. The in situ generated AgNPs due to the acceleration of the reaction kinetics by Cu2+ ions facilitate the growth of Ag14NCs with FCC metallic kernel. These two structural units of AgNCs show light-induced reversible structural transformation which is also associated with the reversible tuning of their spectroscopic and morphological signatures. This PARI-guided interconversion strategy put forward a most appropriate example of a structure-property relationship in MNCs.

An Au25 nanocluster/MoS2 vdWaals heterojunction phototransistor for chromamorphic visual-afterimage emulation

Color vision relies on three cone photoreceptors that are sensitive to different wavelengths of light. The interaction of three incident light wavelengths over time creates a fascinating color coupling perception, termed chromamorphic computing. However, the realization of this fascinating characteristic in semiconductor devices remains a great challenge. Herein, a mixed-dimensional optoelectronic transistor based on a novel metal nanocluster Au25(SC12H25)18 and two-dimensional MoS2 van der Waals (vdWaals) heterojunction is proposed for chromamorphic visual-afterimage emulation with red-green-blue three-color spatiotemporal coupling perception. This distinguished molecular-like electronic level of Au25 nanoclusters allows the transistor to have visible light-sensitive properties, endowing it with the ability to perceive color information. Moreover, the chromamorphic functions are realized using a color spatiotemporal coupling approach. By utilizing the photogating effect of light stimulus, the device exhibits visual experience-dependent plasticity in accordance with the Bienenstock-Cooper-Munro (BCM) learning rule. Most importantly, for the first time, intriguing visual afterimages could be implemented using a color sensitization approach based on a close relationship between visual persistence and negative afterimages. These results represent an important step towards a new generation of intelligent visual color perception systems for human-computer interaction, bionic robots, etc.

Impact of the Peripheral Ligand Layer on the Excited-State Deactivation Mechanism of Au38S2(S-Adm)20 and Au30(S-Adm)18 (S-Adm = Adamantanethiolate) Clusters

Gold nanoclusters are ideal fluorescent labels for biological imaging, disease diagnosis, and treatment. Understanding the origin of the photoluminescence phenomenon in ligand-protected gold nanoclusters is crucial for both basic science and practical applications. In this study, density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were performed to study the mechanism of excited state deactivation of Au38S2(S-Adm)20 and Au30(S-Adm)18 (S-Adm = adamantanethiolate) clusters, which have similar sizes and compositions. The computational results indicate that the differences in structural symmetry and peripheral ligand layer lead to quite different excited state deactivation mechanisms and excited state lifetimes in Au38S2(S-Adm)20 and Au30(S-Adm)18. Specifically, the μ3-S atoms and bridging thiolate (SR) in the ligand layer of Au38S2(S-Adm)20 significantly suppress the structural relaxation of ligand motifs, resulting in a prolonged excited state lifetime and higher quantum yield. For the Au30(S-Adm)18, due to the symmetry forbidden and large structural relaxation of the ligand shell, a rapid nonradiative transition process resulted. This study provides new insights into how the photoluminescence of ligand-protected gold nanoclusters is influenced by their structure and symmetry.

Pivotal Role of Modifiable A-Site Doping in Enhancing Valence Stability and Excited State Dynamics of MnO6

The controlled regulation of A-site in rare earth manganate perovskites can orderly arrange the electronic states, leading to the emergence of unique transport properties. However, it is challenging to balance crystal structure stability and property variations during the multi-ion doping. In this study, a series of multivalent manganate perovskites are synthesized by hydrothermal method through the A-site multielement doping, which enables the manganese atoms with varying valence states to orderly arrange at the B site. Powder X-ray diffraction (PXRD) and X-ray absorption spectra (XAS) confirm that the splitting of the K─O hybrid orbitals in the crystal effectively prevents any distortion of the MnO6 octahedron, thereby facilitating the ordered arrangement of Mn (III) -Mn (IV) -Mn (V) at the B-site and promoting superstructure formation. The transient absorption spectra (TAS) reveals that the sequential arrangement of Mn (III) - Mn (IV) - Mn(V) better forms the charge transfer channels, and thereby makes the photodynamic properties of the sample composition-dependent. These photodynamic properties will facilitate the study of exciton-electron coupling behavior in LCKMO crystals during electrical transport.

Triple-Phosphorescent Gold Nanoclusters Enabled by Isomerization of Terminal Thiouracils in the Surface Motifs

Metal nanoclusters (NCs) hold great promise for expressing multipeak emission based on their well-defined total structure with diverse luminescent centers. Herein, we report the surface motif-dictated triple phosphorescence of Au NCs with dynamic color turning. The deprotonation-triggered isomerization of terminal thiouracils can evolve into a mutual transformation among their hierarchical motifs, thus serving a multipeak-emission expression with good tailoring. More importantly, the underlying electron transfer is thoroughly identified by excluding the radiative and nonradiative energy transfer, where electrons flow from the first phosphorescent state to the last two ones. The findings shed light on finely tailing motifs at the molecular level to motivate studies on customizable luminescence characteristics of metal NCs.

Isomeric Effects of Au28(S-c-C6H11)20 Nanoclusters on Photoluminescence: Roles of Electron-Vibration Coupling and Higher Triplet State

The exploration of near-infrared photoluminescence (PL) from atomically precise nanoclusters is currently a prominent area of interest owing to its importance in both fundamental research and diverse applications. In this work, we investigate the near-infrared (NIR) photoluminescence mechanisms of two structural isomers of atomically precise gold nanoclusters of 28 atoms protected by cyclohexanethiolate (CHT) ligands, i.e., Au28i(CHT)20 and Au28ii(CHT)20. Based on their structures, analysis of 3O2 (triplet oxygen) quenching of the nanocluster triplet states, temperature-dependent photophysical studies, and theoretical calculations, we have elucidated the intricate processes governing the photoluminescence of these isomeric nanoclusters. For Au28i(CHT)20, its emission characteristics are identified as phosphorescence plus thermally activated delayed fluorescence (TADF) with a PL quantum yield (PLQY) of 0.3% in dichloromethane under ambient conditions. In contrast, the Au28ii(CHT)20 isomer exhibits exclusive phosphorescence with a PLQY of 3.7% in dichloromethane under ambient conditions. Theoretical simulations reveal a larger singlet (S1)-triplet (T1) gap in Au28ii than that in Au28i, and the higher T2 state plays a critical role in both isomers' photophysical processes. The insights derived from this investigation not only contribute to a more profound comprehension of the fundamental principles underlying the photoluminescence of atomically precise gold nanoclusters but also provide avenues for tailoring their optical properties for diverse applications.

Evolution of Excited-State Behaviors of Gold Complexes, Nanoclusters and Nanoparticles

Metal nanomaterials have been extensively investigated owing to their unique properties in contrast to bulk counterparts. Gold nanoparticles (e. g., 3-100 nm) show quasi-continuous energy bands, while gold nanoclusters (<3 nm) and complexes exhibit discrete energy levels and display entirely different photophysical properties than regular nanoparticles. This review summarizes the electronic dynamics of these three types of gold materials studied by ultrafast spectroscopy. Briefly, for gold nanoparticles, their electronic relaxation is dominated by heat dissipation between the electrons and the lattice. In contrast, gold nanoclusters exhibit single-electron transitions and relatively long excited-state lifetimes being analogous to molecules. In gold complexes, the excited-state dynamics is dominated by intersystem crossing and phosphorescence. A detailed understanding of the photophysical properties of gold nanocluster materials is still missing and thus calls for future efforts. The fundamental insights into the discrete electronic structure and the size-induced evolution in quantum-sized nanoclusters will promote the exploration of their applications in various fields.

Chemical Flexibility of Atomically Precise Metal Clusters

Ligand-protected metal clusters possess hybrid properties that seamlessly combine an inorganic core with an organic ligand shell, imparting them exceptional chemical flexibility and unlocking remarkable application potential in diverse fields. Leveraging chemical flexibility to expand the library of available materials and stimulate the development of new functionalities is becoming an increasingly pressing requirement. This Review focuses on the origin of chemical flexibility from the structural analysis, including intra-cluster bonding, inter-cluster interactions, cluster-environments interactions, metal-to-ligand ratios, and thermodynamic effects. In the introduction, we briefly outline the development of metal clusters and explain the differences and commonalities of M(I)/M(I/0) coinage metal clusters. Additionally, we distinguish the bonding characteristics of metal atoms in the inorganic core, which give rise to their distinct chemical flexibility. Section 2 delves into the structural analysis, bonding categories, and thermodynamic theories related to metal clusters. In the following sections 3 to 7, we primarily elucidate the mechanisms that trigger chemical flexibility, the dynamic processes in transformation, the resultant alterations in structure, and the ensuing modifications in physical-chemical properties. Section 8 presents the notable applications that have emerged from utilizing metal clusters and their assemblies. Finally, in section 9, we discuss future challenges and opportunities within this area.

Construction of an autofluorescence interference-free phosphorescence biosensor for the specific detection of TK1 mRNA

The anti-interference ability of biosensors is critical for detection in biological samples. Fluorescence-based sensors are subject to interference from self-luminescent substances in biological matrices. Therefore, phosphorescent sensors stand out among biosensors due to their lack of self-luminescence background. In this study, a phosphorescent sensor was constructed, which can accurately detect thymidine kinase 1 (TK1) mRNA in biological samples and avoid autofluorescence interference. When there is no target, polydopamine (PDA) is used as the phosphorescence resonance energy transfer (PRET) acceptor to quench the phosphorescence of the persistently luminescent (PL) nanomaterial. When there is a target, the DNA modified by the PL nanomaterial is replaced by the hairpin H and removed away from the PDA, resulting in a rebound in phosphorescence. The phosphorescent sensor exhibits a good linear relationship in the TK1 mRNA concentration range of 0-200 nM, and the detection limit was 1.74 nM. The sensor fabricated in this study can effectively avoid interference from spontaneous fluorescence in complex biological samples, and sensitively and precisely detect TK1 mRNA in serum samples, providing a powerful tool to more accurately detect biomarkers in biological samples.

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

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

An Au5Ag12(SR)9(dppf)4 alloy nanocluster: structural determination and optical property and photothermal conversion investigation

Photothermal conversion has garnered significant attention due to its potential for efficient energy conversion and application in targeted therapies. However, controlling photothermal properties at the atomic level remains a challenge in current materials synthesis. In this study, we report the synthesis and structural determination of a phosphine and mercaptan co-protected Au5Ag12(SR)9(dppf)4 (Au5Ag12) nanocluster with an extremely low quantum yield (∼0%). For comparative purposes, we synthesized three alloy nanoclusters of similar size. Notably, Au5Ag12 demonstrates a remarkably superior photothermal conversion performance, significantly outperforming the other clusters. We investigated this variance from both absorption and emission perspectives. This research not only opens new avenues for the application of clusters with extremely low quantum yields, but also provides experimental evidence for understanding the photothermal conversion properties of cluster materials at the atomic level.

Beyond the promise: Exploring the complex interactions of nanoparticles within biological systems

The exploration of nanoparticle applications is filled with promise, but their impact on the environment and human health raises growing concerns. These tiny environmental particles can enter the human body through various routes, such as the respiratory system, digestive tract, skin absorption, intravenous injection, and implantation. Once inside, they can travel to distant organs via the bloodstream and lymphatic system. This journey often results in nanoparticles adhering to cell surfaces and being internalized. Upon entering cells, nanoparticles can provoke significant structural and functional changes. They can potentially disrupt critical cellular processes, including damaging cell membranes and cytoskeletons, impairing mitochondrial function, altering nuclear structures, and inhibiting ion channels. These disruptions can lead to widespread alterations by interfering with complex cellular signaling pathways, potentially causing cellular, organ, and systemic impairments. This article delves into the factors influencing how nanoparticles behave in biological systems. These factors include the nanoparticles' size, shape, charge, and chemical composition, as well as the characteristics of the cells and their surrounding environment. It also provides an overview of the impact of nanoparticles on cells, organs, and physiological systems and discusses possible mechanisms behind these adverse effects. Understanding the toxic effects of nanoparticles on physiological systems is crucial for developing safer, more effective nanoparticle-based technologies.

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.

Three-atom-wide gold quantum rods with periodic elongation and strongly polarized excitons

Atomically precise control over anisotropic nanoclusters constitutes a grand challenge in nanoscience. In this work, we report our success in achieving a periodic series of atomically precise gold quantum rods (abbrev. Au QRs) with unusual excitonic properties. These QRs possess hexagonal close-packed kernels with a constant three-atom diameter but increasing aspect ratios (ARs) from 6.3 to 18.7, all being protected by the same thiolate (SR) ligand. The kernels of the QRs are in a Au1-(Au3)n-Au1 configuration (where n is the number of Au3 layers) and follow a periodic elongation with a uniform Au18(SR)12 increment consisting of four Au3 layers. These Au QRs possess distinct HOMO-LUMO gaps (Eg = 0.6 to 1.3 eV) and exhibit strongly polarized excitonic transition along the longitudinal direction, resulting in very intense absorption in the near-infrared (800 to 1,700 nm). While excitons in gapped systems and plasmons in gapless systems are distinctly different types of excitations, the strongly polarized excitons in Au QRs surprisingly exhibit plasmon-like behaviors manifested in the shape-induced polarization, very intense absorption (~106 M-1 cm-1), and linear scaling relations with the AR, all of which resemble the behaviors of conventional metallic-state Au nanorods (i.e., gapless systems), but the QRs possess distinct gaps and very long excited-state lifetimes (10 to 2,122 ns), which hold promise in applications such as near-infrared solar energy utilization, hot carrier generation and transfer. The observation of plasmon-like behaviors from single-electron transitions in Au QRs elegantly bridges the distinct realms of single-electron and collective-electron excitations and may stimulate more research on excitonics and plasmonics.

Atomically precise photothermal nanomachines

Interfacing molecular machines to inorganic nanoparticles can, in principle, lead to hybrid nanomachines with extended functions. Here we demonstrate a ligand engineering approach to develop atomically precise hybrid nanomachines by interfacing gold nanoclusters with tetraphenylethylene molecular rotors. When gold nanoclusters are irradiated with near-infrared light, the rotation of surface-decorated tetraphenylethylene moieties actively dissipates the absorbed energy to sustain the photothermal nanomachine with an intact structure and steady efficiency. Solid-state nuclear magnetic resonance and femtosecond transient absorption spectroscopy reveal that the photogenerated hot electrons are rapidly cooled down within picoseconds via electron-phonon coupling in the nanomachine. We find that the nanomachine remains structurally and functionally intact in mammalian cells and in vivo. A single dose of near-infrared irradiation can effectively ablate tumours without recurrence in tumour-bearing mice, which shows promise in the development of nanomachine-based theranostics.

Nonadiabatic Molecular Dynamics with Non-Condon Effect of Charge Carrier Dynamics

Nonradiative multiphonon transitions play a crucial role in understanding charge carrier dynamics. To capture the non-Condon effect in nonadiabatic molecular dynamics (NA-MD), we develop a simple and accurate method to calculate noncrossing and crossing k-point NA coupling in momentum space on an equal footing and implement it with a trajectory surface hopping algorithm. Multiple k-point MD trajectories can provide sufficient nonzero momentum multiphonons coupled to electrons, and the momentum conservation is maintained during nonvertical electron transition. The simulations of indirect bandgap transition in silicon and intra- and intervalley transitions in graphene show that incorporation of the non-Condon effect is needed to correctly depict these types of charge dynamics. In particular, a hidden process is responsible for the delayed nonradiative electron-hole recombination in silicon: the thermal-assisted rapid trapping of an excited electron at the conduction band minimum by a long-lived higher energy state through a nonvertical transition extends charge carrier lifetime, approaching 1 ns, which is about 1.5 times slower than the direct bandgap recombination. For graphene, intervalley scattering takes place within about 225 fs, which can occur only when the intravalley relaxation proceeds to about 50 fs to gain enough phonon momentum. The intra- and intervalley scattering constitute energy relaxation, which completes within sub-500 fs. All the simulated time scales are in excellent agreement with experiments. The study establishes the underlying mechanisms for a long-lived charge carrier in silicon and valley scattering in graphene and underscores the robustness of the non-Condon approximation NA-MD method, which is suitable for rigid, soft, and large defective systems.

Tailoring Carbon Tails of Ligands on Au52(SR)32 Nanoclusters Enhances the Near-Infrared Photoluminescence Quantum Yield from 3.8 to 18.3

One of the important factors that determine the photoluminescence (PL) properties of gold nanoclusters pertain to the surface. In this study, four Au52(SR)32 nanoclusters that feature a series of aromatic thiolate ligands (-SR) with different bulkiness at the para-position are synthesized and investigated. The near-infrared (NIR) photoluminescence (peaks at 900-940 nm) quantum yield (QY) is largely enhanced with a decrease in the ligand's para-bulkiness. Specifically, the Au52(SR)32 capped with the least bulky p-methylbenzenethiolate (p-MBT) exhibits the highest PLQY (18.3% at room temperature in non-degassed dichloromethane), while Au52 with the bulkiest tert-butylbenzenethiolate (TBBT) only gives 3.8%. The large enhancement of QY with fewer methyl groups on the ligands implies a nonradiative decay via the multiphonon process mediated by C-H bonds. Furthermore, single-crystal X-ray diffraction (SCXRD) comparison of Au52(p-MBT)32 and Au52(TBBT)32 reveals that fewer methyl groups at the para-position lead to a stronger interligand π···π stacking on the Au52 core, thus restricting ligand vibrations and rotations. The emission nature is identified to be phosphorescence and thermally activated delayed fluorescence (TADF) based on the PL lifetime, 3O2 quenching, and temperature-dependent PL and absorption studies. The 1O2 generation efficiencies for the four Au52(SR)32 NCs follow the same trend as the observed PL performance. Overall, the highly NIR-luminescent Au52(p-MBT)32 nanocluster and the revealed mechanisms are expected to find future applications.

Ultra-Sensitive Portable Visual Paper-Based Viral Molecularly Imprinted Sensor without Autofluorescence Interference

Detection of the virus is the primary factor to discover and block the occurrence and development of the virus epidemic. Here, an ultrasensitive paper-based virus molecular imprinting sensor is developed to detect two viruses simultaneously in which the detection limit of the influenza virus (H5N1) is 16.0 aM (9.63 × 103 particles/mL) while that of the Hepatitis B Virus (HBV) is 129 fM (7.77 × 107 particles/mL). This paper-based sensor is low cost and is easy to cut, store, and carry. In addition, the visual semiquantitative detection of two viruses is achieved by using two aptamer-functionalized persistent luminescent nanoparticles as signal probes. These probes and the imprinted cavities on the paper-based material formed sandwich-type double recognition of the target viruses. This sensor has extremely high sensitivity to the H5N1 virus, which is of great value to solve the influenza epidemic with the most outbreaks in history, and also opens up a new way for the prevention and control of other virus epidemics. This cheap and portable visual sensor provides the possibility for self-service detection and can greatly reduce the pressure on medical staff and reduce the risk of virus infection caused by the concentration of people to be tested.

Customizing a Hyperbranched Ligand Confers Supported Platinum Nanoclusters with Unexpected Catalytic Activity toward the Reduction of 4-Nitrophenol

We here show that a dendritic molecule combined with ligand merit confers supported platinum nanoclusters (PtNCs) with unprecedented catalytic performance. Branched polyethylenimine (PEI, Mn = 2000 D) patched on a porous bead is modified with 2-(diphenylphosphino)benzaldehyde (dppb) before being used to mediate a platinum nanoparticle/nanocluster (Pt0). The catalytic activity of Pt0 toward the reduction of 4-nitrophenol (4-NP) is evaluated from the parameter of Pt-normalized rate constant (kc). Optimization of the dppb level along with transformation of the PEI hydrogens into diol or trimethylammonium groups imparts supported Pt0 unprecedented activity (kc = 19.2 L mmol-1 s-1 and turnover frequency (TOF) = 1041 h-1). The supported Pt0 at an extremely low dosage of 0.1 ppm promotes 98% conversion of 4-NP within minutes and is well recyclable. The striking catalytic activity is attributed to the combination of orthogonal ligand properties such as weak ligand nature, catalyst-activating ability, excellent substrate affinity, and effect on PtNC-size mediation of the ligand.

Core-Packing-Related Vibrational Properties of Thiol-Protected Gold Nanoclusters and Their Excited-State Behavior

Thiolate-protected gold nanoclusters, with unique nuclearity- and structure-dependent properties, have been extensively used in energy conversion and catalysis; however, the mystery between kernel structures and properties remains to be revealed. Here, the influence of core packing on the electronic structure, vibrational properties, and excited-state dynamics of four gold nanoclusters with various kernel structures is explored using density functional theory combined with time-domain nonadiabatic molecular dynamics simulations. We elucidate the correlation between the geometrical structure and excited-state dynamics of gold nanoclusters. The distinct carrier lifetimes of the four nanoclusters are attributed to various electron-phonon couplings arising from the different vibrational properties caused by core packing. We have identified specific phonon modes that participate in the electron-hole recombination dynamics, which are related to the gold core of nanoclusters. This study paints a physical picture from the geometric configuration, electronic structure, vibrational properties, and carrier lifetime of these nanoclusters, thereby facilitating their potential application in optoelectronic materials.

A Review on Gold Nanoclusters for Cancer Phototherapy

Cancer phototherapy, including photodynamic therapy (PDT) and photothermal therapy (PTT), has been extensively studied in recent years because of its noninvasive properties, high efficiency, improved selectivity, and reduced side effects. Gold nanoclusters (AuNCs) have the advantages of high biocompatibility, high biosafety, excellent photoresponse, and high tumor penetration ability. This review analyzes the use of AuNCs in tumor phototherapy in recent years from three aspects, namely, AuNCs in PDT, AuNCs in PTT, and AuNCs in combination therapy, and presents the high potential of AuNCs in cancer phototherapy. This review aims to provide readers with the unique advantages, diversified application approaches, and bright application prospects of AuNCs in phototherapy and to provide insights into strategies for applying AuNCs to tumor phototherapy.

Formation and Growth of Atomic Scale Seeds of Au Nanoparticle in the Nanospace of an Organic Cage Molecule

Seed-mediated growth has been widely used to synthesize noble metal nanoparticles with controlled size and shape. Although it is becoming possible to directly observe the nucleation process of metal atoms at the single atom level by using transmission electron microscopy (TEM), it is challenging to control the formation and growth of seeds with only a few metal atoms in homogeneous solution systems. This work reports site-selective formation and growth of atomic scale seeds of the Au nanoparticle in a nanospace of an organic cage molecule. We synthesized a cage molecule with amines and phenols, which were found to both capture and reduce Au(III) ions to spontaneously form the atomic scale seeds containing Au(0) in the nanospace. The growth reaction of the atomic scale seeds afforded Au nanoparticles with an average diameter of 2.0±0.2 nm, which is in good agreement with the inner diameter of the cage molecule.

Intrinsic Optical Properties and Emerging Applications of Gold Nanostructures

The collective oscillation of free electrons at the nanoscale surface of gold nanostructures is closely modulated by tuning the size, shape/morphology, phase, composition, hybridization, assembly, and nanopatterning, along with the surroundings of the plasmonic surface located at a dielectric interface with air, liquid, and solid. This review first introduces the physical origin of the intrinsic optical properties of gold nanostructures and further summarizes stimuli-responsive changes in optical properties, metal-field-enhanced optical signals, luminescence spectral shaping, chiroptical response, and photogenerated hot carriers. The current success in the landscape of nanoscience and nanotechnology mainly originates from the abundant optical properties of gold nanostructures in the thermodynamically stable face-centered cubic (fcc) phase. It has been further extended by crystal phase engineering to prepare thermodynamically unfavorable phases (e.g., kinetically stable) and heterophases to modulate their intriguing phase-dependent optical properties. A broad range of promising applications, including but not limited to full-color displays, solar energy harvesting, photochemical reactions, optical sensing, and microscopic/biomedical imaging, have fostered parallel research on the multitude of physical effects occurring in gold nanostructures.

General Method to Synthesize Highly Stable Nanoclusters via Pickering-Stabilized Microemulsions

The ability to not only control but also maintain the well-defined size of nanoclusters is key to a scientific understanding as well as their practical application. Here, we report a synthetic protocol to prepare and stabilize nanoclusters of different metals and even metal salts. The approach builds on a Pickering stabilization effect inside a microemulsion system. We prove that the emulsion interface plays a critical role in the formation of nanoclusters, which are encapsulated in situ into a silica matrix. The resulting nanocapsule is characterized by a central cavity and a porous shell composed of a matrix of both silica and nanoclusters. This structure endows the nanoclusters simultaneously with high thermal stability, good biocompatibility, and excellent photostability, making them well suited for fundamental studies and practical applications ranging from materials chemistry, catalysis, and optics to bioimaging.

Atomically precise gold nanoclusters at the molecular-to-metallic transition with intrinsic chirality from surface layers

The advances in determining the total structure of atomically precise metal nanoclusters have prompted extensive exploration into the origins of chirality in nanoscale systems. While chirality is generally transferrable from the surface layer to the metal-ligand interface and kernel, we present here an alternative type of gold nanoclusters (138 gold core atoms with 48 2,4-dimethylbenzenethiolate surface ligands) whose inner structures are not asymmetrically induced by chiral patterns of the outermost aromatic substituents. This phenomenon can be explained by the highly dynamic behaviors of aromatic rings in the thiolates assembled via π - π stacking and C - H···π interactions. In addition to being a thiolate-protected nanocluster with uncoordinated surface gold atoms, the reported Au₁₃₈ motif expands the size range of gold nanoclusters having both molecular and metallic properties. Our current work introduces an important class of nanoclusters with intrinsic chirality from surface layers rather than inner structures and will aid in elucidating the transition of gold nanoclusters from their molecular to metallic states.

Size Effects of Atomically Precise Gold Nanoclusters in Catalysis

The emergence of ligand-protected, atomically precise gold nanoclusters (NCs) in recent years has attracted broad interest in catalysis due to their well-defined atomic structures and intriguing properties. Especially, the precise formulas of NCs provide an opportunity to study the size effects at the atomic level without complications by the polydispersity in conventional nanoparticles that obscures the relationship between the size/structure and properties. Herein, we summarize the catalytic size effects of atomically precise, thioate-protected gold NCs in the range of tens to hundreds of metal atoms. The catalytic reactions include electrochemical catalysis, photocatalysis, and thermocatalysis. With the precise sizes and structures, the fundamentals underlying the size effects are analyzed, such as the surface area, electronic properties, and active sites. In the catalytic reactions, one or more factors may exert catalytic effects simultaneously, hence leading to different catalytic-activity trends with the size change of NCs. The summary of literature work disentangles the underlying fundamental mechanisms and provides insights into the size effects. Future studies will lead to further understanding of the size effects and shed light on the catalytic active sites and ultimately promote catalyst design at the atomic level.

Luminescent Gold Nanoclusters for Bioimaging: Increasing the Ligand Complexity

Fluorescence, and more in general, photoluminescence (PL), presents important advantages for imaging with respect to other diagnostic techniques. In particular, detection methodologies exploiting fluorescence imaging are fast and versatile; make use of low-cost and simple instrumentations; and are taking advantage of newly developed powerful, low-cost, light-based electronic devices, such as light sources and cameras, used in huge market applications, such as civil illumination, computers, and cellular phones. Besides the aforementioned simplicity, fluorescence imaging offers a spatial and temporal resolution that can hardly be achieved with alternative methods. However, the two main limitations of fluorescence imaging for bio-application are still (i) the biological tissue transparency and autofluorescence and (ii) the biocompatibility of the contrast agents. Luminescent gold nanoclusters (AuNCs), if properly designed, combine high biocompatibility with PL in the near-infrared region (NIR), where the biological tissues exhibit higher transparency and negligible autofluorescence. However, the stabilization of these AuNCs requires the use of specific ligands that also affect their PL properties. The nature of the ligand plays a fundamental role in the development and sequential application of PL AuNCs as probes for bioimaging. Considering the importance of this, in this review, the most relevant and recent papers on AuNCs-based bioimaging are presented and discussed highlighting the different functionalities achieved by increasing the complexity of the ligand structure.

Investigation of plasmon relaxation mechanisms using nonadiabatic molecular dynamics

Hot carriers generated from the decay of plasmon excitation can be harvested to drive a wide range of physical or chemical processes. However, their generation efficiency is limited by the concomitant phonon-induced relaxation processes by which the energy in excited carriers is transformed into heat. However, simulations of dynamics of nanoscale clusters are challenging due to the computational complexity involved. Here, we adopt our newly developed Trajectory Surface Hopping (TSH) nonadiabatic molecular dynamics algorithm to simulate plasmon relaxation in Au20 clusters, taking the atomistic details into account. The electronic properties are treated within the Linear Response Time-Dependent Tight-binding Density Functional Theory (LR-TDDFTB) framework. The relaxation of plasmon due to coupling to phonon modes in Au20 beyond the Born–Oppenheimer approximation is described by the TSH algorithm. The numerically efficient LR-TDDFTB method allows us to address a dense manifold of excited states to ensure the inclusion of plasmon excitation. Starting from the photoexcited plasmon states in Au20 cluster, we find that the time constant for relaxation from plasmon excited states to the lowest excited states is about 2.7 ps, mainly resulting from a stepwise decay process caused by low-frequency phonons of the Au20 cluster. Furthermore, our simulations show that the lifetime of the phonon-induced plasmon dephasing process is ∼10.4 fs and that such a swift process can be attributed to the strong nonadiabatic effect in small clusters. Our simulations demonstrate a detailed description of the dynamic processes in nanoclusters, including plasmon excitation, hot carrier generation from plasmon excitation dephasing, and the subsequent phonon-induced relaxation process.

Origin of the polychromatic photoluminescence of zeolite confined Ag clusters: temperature- and co-cation-dependent luminescence

Zeolite confined silver clusters (AgCLs) have attracted extensive attention due to their remarkable luminescent properties, but the elucidation of the underlying photophysical processes and especially the excited-state dynamics remains a challenge. Herein, we investigate the bright photoluminescence of AgCLs confined in Linde Type A zeolites (LTA) by systematically varying the temperature (298-77 K) and co-cation composition (Li/Na) and examining their respective influence on the steady-state and time-resolved photoluminescence. The observed polychromatic emission of the tetrahedral Ag4(H2O) n 2+ clusters ranges from orange to violet and three distinct emitting species are identified, corresponding to three long-lived triplet states populated consecutively and separated by a small energy barrier. These long-lived species are at the origin of the polychromatic luminescence with high photoluminescence quantum yields. Furthermore, the Li-content dependence of decay times points to the importance of guest-host-guest interactions in tuning the luminescent properties with a 43% decrease of the dominating decay time by increasing Li content. Based on our findings, a simplified model for the photophysical kinetics is proposed that identifies the excited-state processes. The results outlined here pave the way for a rational design of confined metal clusters in various frames and inspire the specified applications of Ag-zeolites.

A nanoarchitecture of a gold cluster conjugated gold nanorod hybrid system and its application in fluorescence imaging and plasmonic photothermal therapy

Engineering different nanomaterials into a single functional material can impart unique properties of the parental nanoparticles, especially in the field of bio imaging and therapy. Gold nanomaterials having different sizes, shapes and dimensionalities exhibit exceptional properties apart from their non-toxicity and hence are strong candidates in the biomedical field. Designing a hybrid nanomaterial of two gold nanostructures retaining the individual properties of the parental nanomaterials is challenging. Here, we demonstrate the synthesis of a hybrid nanomaterial (GQC@GNR), comprising an extremely small gold nanocluster and a representative of the asymmetric gold nanostructure, i.e., a gold nanorod, both having their own different exclusive optical properties like tuneable emission and NIR absorption characteristics, respectively. The hybrid system is designed to retain its emission and absorption in the NIR region to use it as an agent for simultaneous imaging and therapy. The formation of GQC@GNR and its architectonics heavily depend on the synthesis route and the parameters adopted which in turn have a direct influence on its properties. The architecture and its connection to the optical properties are explained using UV-Vis absorption and photoluminescence spectroscopy, zeta potential, transmission electron microscopy, etc. DFT-based computational modelling supports architectonics as explained by the experimental findings. The formation of the gold-gold hybrid system witnessed interesting science with a strong indication that materials with desired properties can be designed by appropriately modulating the architectonics of hybrid formation. Finally, folate conjugated GQC@GNR demonstrated its efficacy for targeted imaging and photothermal therapy in HeLa cells and tumor-bearing animal models. The detailed therapeutic efficacy of GQC@GNR is also explained based on Raman spectroscopy.

Tuning photoelectron dynamic behavior of thiolate-protected MAu24 nanoclusters via heteroatom substitution

Heteroatom substitution of gold nanoclusters enables precise tuning of their physicochemical properties at the single-atom level, which has a significant impact on the applications related to excited states including photovoltaics, photocatalysis and photo-luminescence. To this end, understanding the effect of metal exchange on the structures, electronic properties and photoexcited dynamic behavior of nanoclusters is imperative. Combining density functional theory with time-domain nonadiabatic molecular dynamics simulations, herein we explored the effect of metal replacement on the electronic and vibrational properties as well as excited-state dynamics of ligand-protected MAu₂₄(SR)₁₈ (M = Pd, Pt, Cd, and Hg) nanoclusters. At the atomistic level, we elucidate hot carrier relaxation and recombination dynamic behavior with various doping atoms. Such distinct excited-state behavior of MAu₂₄(SR)₁₈ nanoclusters is attributed to different energy gaps and electron-phonon coupling between the donor and acceptor energy levels, owing to the perturbation of nanoclusters by a single foreign atom. The specific phonon modes involved in excited-state dynamics have been identified, which are associated with the MAu₁₂ core and ligand rings. This time-dependent excited-state dynamic study fills the gap between structure/composition and excited-state dynamic behavior of MAu₂₄(SR)₁₈ nanoclusters, which would stimulate the exploration of their applications in photoenergy storage and conversion.

Atomically Precise Au42 Nanorods with Longitudinal Excitons for an Intense Photothermal Effect

Metallic-state gold nanorods are well known to exhibit strong longitudinal plasmon excitations in the near-infrared region (NIR) suitable for photothermal conversion. However, when the size decreases below ∼2 nm, Au nanostructures become nonmetallic, and whether the longitudinal excitation in plasmonic nanorods can be inherited is unknown. Here, we report atomically precise rod-shaped Au₄₂(SCH₂Ph)₃₂ with a hexagonal-close-packed Au₂₀ kernel of aspect ratio as high as 6.2, which exhibits an intense absorption at 815 nm with a high molar absorption coefficient of 1.4 × 10⁵ M^-1 cm^-1. Compared to other rod-shaped nanoclusters, Au₄₂ possesses a much more effective photothermal conversion with a large temperature increase of ∼27 °C within 5 min (λ_ex = 808 nm, 1 W cm^-2) at an ultralow concentration of 50 μg mL^-1 in toluene. Density functional theory calculations show that the NIR transition is mainly along the long axis of the Au₂₀ kernel in Au₄₂, i.e., a longitudinal excitonic oscillation, akin to the longitudinal plasmon in metallic-state nanorods. Transient absorption spectroscopy reveals that the fast decay in Au₄₂ is similar to that of shorter-aspect-ratio nanorods but is followed by an additional slow decay with a long lifetime of 2400 ns for the Au₄₂ nanorod. This work provides the first case that an intense longitudinal excitation is obtained in molecular-like nanorods, which can be used as photothermal converters and hold potential in biomedical therapy, photoacoustic imaging, and photocatalysis.

Interactions of Metal Nanoclusters with Light: Fundamentals and Applications

The interactions of materials with light determine their applications in various fields. In the past decade, ultrasmall metal nanoclusters (NCs) have emerged as a promising class of optical materials due to their unique molecular-like properties. Herein, the basic principles of optical absorption and photoluminescence of metal NCs, their interactions with polarized light, and light-induced chemical reactions, are discussed, highlighting the roles of the core and protecting ligands/motifs of metal NCs in their interactions with light. The metal core and protecting ligands/motifs determine the electronic structures of metal NCs, which are closely related to their optical properties. In addition, the protecting ligands/motifs of metal NCs contribute to their photoluminescence and chiral origin, further promoting the interactions of metal NCs with light through various pathways. The fundamentals of light-NC interactions provide guidance for the design of metal NCs in optical applications, which are discussed in the second part. In the last section, some strategies are proposed to further understand light-NC interactions, highlighting the challenges and opportunities. It is hoped that this work will stimulate more research on the optical properties of metal NCs and their applications in various fields.

Ligand Shell Isomerization Induces Different Fluorescence Origins of Two Au28 Nanoclusters

Understanding the origin of the photoluminescence (PL) phenomenon in ligand-protected metal nanoclusters is of paramount importance in both fundamental science and practical applications. In this study, we have studied the origin of fluorescence emission of two thiolate-ligand-protected Au₂₈ clusters (Au₂₈(CHT)₂₀ and Au₂₈(TBBT)₂₀) by means of density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. Theoretical calculation results show that the ligand shell isomerization induces different ligand motif-to-metal core charge transfers (LMCT) of Au₂₈(TBBT)₂₀ and Au₂₈(CHT)₂₀. Moreover, in Au₂₈(CHT)₂₀, the emission process of S₂ → S₀ can compete favorably with the internal conversion of S₂ → S₁. Furthermore, the high quantum yield of Au₂₈(CHT)₂₀ is attributed to its high symmetric structure, which leads to less energy dissipation during the structural relaxation process.

Atomic structure of a seed-sized gold nanoprism

The growth of nanoparticles along one or two directions leads to anisotropic nanoparticles, but the nucleation (i.e., the formation of small seeds of specific shape) has long been elusive. Here, we show the total structure of a seed-sized Au₅₆ nanoprism, in which the side Au{100} facets are surrounded by bridging thiolates, whereas the top/bottom {111} facets are capped by phosphine ligands at the corners and Br⁻ at the center. The bromide has been proved to be the key to effectively stabilize the Au{111} to fulfill a complete face-centered-cubic core. In femtosecond electron dynamics analysis, the non-evolution of transient absorption spectra of Au₅₆ is similar to that of larger-sized gold nanoclusters (n > 100), which is ascribed to the completeness of the prismatic Au₅₆ core and an effective electron relaxation pathway created by the stronger Au-Au bonds inside. This work provides some insights for the understanding of plasmonic nanoprism formation.

The formation pathway of shape-anisotropic nanoparticles is difficult to characterize and not well understood. The authors synthesize a prismatic-shaped Au₅₆ nanocluster as possible seed of a prismatic nanoparticle and characterize the structure and ligand bonding motifs, providing insight into the formation and surface protection mechanisms.

Master key to coinage metal nanoclusters treasure chest: 38-metal clusters

Atomically precise metal nanoclusters with specific chemical compositions have become a popular research topic due to their precise structures, attractive properties, and wide range of applications in various fields. Currently, among more than 100 reported metal nanoclusters with precise formulas, 38-atom coinage metal nanoclusters stand out due to their unique structural diversities, such as face-centered cubic (FCC) and body-centered cubic (BCC) arrangements. Among them, the formation of the metal cores includes vertex-sharing, face-fusion, and FCC cubes fusion. Due to their geometrical features, 38-atom coinage metal nanoclusters exhibit attractive properties, making them an ideal model for exploring structure-property relationships. Therefore, 38-atom coinage metal nanoclusters are a universal key to the treasure trove of nanoclusters, which can open almost all fields and are of great research significance. This paper focuses on the structure of 38-atom coinage metal nanoclusters and reviews the preparation and crystallization methods, excellent properties, and practical applications. Finally, future research prospects and development opportunities are provided.

Ultrasmall Luminescent Metal Nanoparticles: Surface Engineering Strategies for Biological Targeting and Imaging

In the past decade, ultrasmall luminescent metal nanoparticles (ULMNPs, d < 3 nm) have achieved rapid progress in addressing many challenges in the healthcare field because of their excellent physicochemical properties and biological behaviors. With the sharp shrinking size of large plasmonic metal nanoparticles (PMNPs), the contributions from the surface characteristics increase significantly, which brings both opportunities and challenges in the application-driven surface engineering of ULMNPs toward advanced biological applications. Here, the systematic advancements in the biological applications of ULMNPs from bioimaging to theranostics are summarized with emphasis on the versatile surface engineering strategies in the regulation of biological targeting and imaging performance. The efforts in the surface functionalization strategies of ULMNPs for enhanced disease targeting abilities are first discussed. Thereafter, self-assembly strategies of ULMNPs for fabricating multifunctional nanostructures for multimodal imaging and nanomedicine are discussed. Further, surface engineering strategies of ratiometric ULMNPs to enhance the imaging stability to address the imaging challenges in complicated bioenvironments are summarized. Finally, the phototoxicity of ULMNPs and future perspectives are also reviewed, which are expected to provide a fundamental understanding of the physicochemical properties and biological behaviors of ULMNPs to accelerate their future clinical applications in healthcare.

Emergent properties in supercrystals of atomically precise nanoclusters and colloidal nanocrystals

We provide a comprehensive account of the optical, electrical and mechanical properties that result from the self-assembly of colloidal nanocrystals or atomically precise nanoclusters into crystalline arrays with long-range order....