Ultrasmall Metal Research Articles

Scalable Synthesis of Ultrasmall Metal Oxide Radio-Enhancers Outperforming Gold

Nanoparticle-based radio-enhancement has the potential to improve cancer cell eradication by augmenting the photoelectric cross-section of targeted cancer cells relative to the healthy surroundings. Encouraging results have been reported for various nanomaterials, including gold and hafnia. However, the lack of scalable synthesis methods and comparative studies is prohibitive to rationalized material design and hampers translation of this promising cancer management strategy. Here, we present a scalable (>100 g day–1) and sterile alternative to conventional batch synthesis of group IV metal oxides (TiO2, ZrO2, and HfO2), which yields near-monodisperse ultrasmall metal oxide nanoparticles with radio-enhancement properties. Access to group IV oxide nanoparticles, which solely differ in atomic number but otherwise exhibit comparable morphologies, sizes, and surface chemistries, enables the direct comparison of their radio-enhancement properties to rationally guide material selection for optimal radio-enhancement performance. We show that the metal oxide nanoparticles exhibit atomic-number-dependent radio-enhancement in cancer cells (HT1080 and HeLa), which is attenuated to baseline levels in normal fibroblasts (normal human dermal fibroblasts). The observed radio-enhancement effects show excellent agreement with physical dose enhancement and nanoparticle dosimetry calculations. Direct benchmarking against gold nanoparticles, the current gold standard in the field, rationalizes the use of hafnia nanoparticles based on their radio-enhancement performance, which is superior to equi-sized gold nanoparticles. Taken together, the competitive radio-enhancement properties for near-monodisperse nanoparticles produced by scalable and sterile flame spray synthesis offer a route to overcoming key roadblocks in the translation of nanoparticle-based radio-enhancers.

Compression‐Driven Internanocluster Reaction for Synthesis of Unconventional Gold Nanoclusters

AbstractCan the active kernels in ultrasmall metal nanoparticles (nanoclusters, NCs) react with one another, or can the internanocluster reaction occur when they are in close enough proximity? To resolve this fundamental issue, we investigated the solid‐state internanocluster reaction of the most studied gold NC Au25(SR)18 (SR: thiolate). A novel NC was produced by increasing the pressure to 5 GPa, whose composition was determined to be Au32(SC2H4Ph)24 by mass spectrometry and thermogravimetric analysis. As revealed by single‐crystal X‐ray crystallography, the structure, a bicuboid Au14 kernel and three pairs of interlocked trimetric staples, has not been reported and endows the NC with obvious photoluminescence. DFT calculations indicate that the staples contribute substantially to the absorption properties. Further experiments reveal the pressure (internanocluster distance) can tune the internanocluster reaction, and the resulting product is not necessarily the thermodynamic product.

Mesoporous carbon-supported ultrasmall metal nanoparticles via a mechanochemical-driven redox reaction: A “Two-in-One” strategy

Mesoporous carbon supported ultrasmall metal nanoparticles (MNPs) are attracting interests in various catalytic applications. Traditional synthetic methods usually involve tedious and time-consuming procedures. Therefore, it remains a grand challenge to prepare well-defined ultrasmall MNPs on mesoporous carbon support. Here, we successfully synthesized a series of mesoporous carbon-supported ultrasmall noble MNPs including Rh, Ru and Pd via a “Two-in-One” strategy which combines the synthesis of mesoporous carbon with ultrasmall MNPs based on a facile mechanochemical method. The key here is to employ CaC2 as both a carbon source for the construction of porous carbon network and an efficient reducing agent to facilitate the formation of ultrasmall MNPs via a solid-state redox reaction. This method circumvent high-temperature pyrolysis and other tedious procedures for the preparation of mesoporous carbon and MNPs, thus representing a versatile, ultrafast, and scalable strategy. Interestingly, the as-prepared Rh-BM-C after ball milling (BM) exhibits an extraordinary low-overpotential of 28 mV@10 mA cm−2 as well as a remarkable turnover frequency (TOF) value of 2.6 H2 s-1@50 mV for hydrogen evolution. Density functional theory (DFT) calculations reveal that nitrogen-doping, type of noble metal and synergistic effect between metal layer and carbon support play a critical role in achieving this compelling HER performance.

The beauty of binary phases: A facile strategy for synthesis, processing, functionalization, and application of ultrasmall metal nanoclusters

• An overview of the two-phase strategies for ultrasmall metal nanoclusters. • The two-phase synthesis, processing, functionalization, and application of metal nanoclusters. • The challenges and prospects related to the two-phase strategies for metal nanoclusters. Ultrasmall metal nanoclusters (NCs) are a sub-class of metal nanoparticles (NPs) with a metal core size of ≤3 nm, and display interesting molecule-like properties. Atomically precise metal NCs can be synthesized by many solution chemistry methods in polar and non-polar reaction environments. Among these methods, two-phase based strategies involving a water-oil binary reaction system have emerged as a facile means to synthesize, process, functionalize, and apply metal NCs. This Review firstly presents an overview of the two-phase based strategies in the synthesis of hydrophobic and hydrophilic metal NCs, and aims to elucidate the underlying working principles of these strategies. Then, how a two-phase system could process metal NCs for size/composition tailoring, luminescence generation, sorting and purification is discussed. Subsequently, several examples that utilizing a two-phase system to efficiently functionalize metal NCs with different surface chemistry are highlighted. Finally, two-phase based applications of metal NCs in catalysis and self-assembly are also reviewed. The fundamentals and the advances of the two-phase based strategies in the synthesis, processing, functionalization, and application of metal NCs summarized in this Review may increase the acceptance of two-phase based strategy in the metal NC field.

Statistical odd-even staggering in few fermions systems

The odd-even staggering (OES) in nuclear binding energies is a well-known fact. A rather similar effect can be found in other finite fermion systems. For instance, ultra small metallic grains and metal clusters. The staggering in nuclei and grains is attributed primarily to pairing correlations. In clusters, it is originated by the Jahn–Teller effect [Phys. Rev. Lett. 81, 3599 (1998)]. Here, we work with a simple, Lipkin-like, exactly solvable two-level fermion model. A statistical mechanics’ treatment of it shows that OES effects also emerge here, as revealed by theoretical tools connected with the so-called statistical complexity.

Induction of apoptosis in Trypanosoma brucei following endocytosis of ultra-small noble metal nanoclusters

Trypanosoma brucei, the causative agent of African trypanosomiasis, is a unicellular protozoan with an intricate life cycle involving an insect vector and mammalian hosts. Trypanosomiasis remains a threat to the health of human beings and animals. Despite the rapid development of nanomedicine, there are few valuable reports on the application of nanoscience in protozoa, especially the lack of understanding of the mechanism. In this study, we investigated the endocytosis of two noble metal nanoclusters (NM-NCs), Ag2[email protected] and [email protected] in T. brucei. Both types of NC can be efficiently up-taken by T. brucei via a clathrin-dependent endocytosis pathway, and displayed in a dose-dependent anti-parasitic manner by inducing pathological alterations to apoptosis-associated organelles. The Ag2[email protected] mainly interacted with functional proteins in the mitochondrion and endoplasmic reticulum, while the [email protected] predominantly interfered with the biological activity of cytoplasmic enzymes involved in mRNA maturation, protein degradation and signal transduction. These data not only reveal the clathrin-dependent endocytosis pathway in T. brucei, but also open up a new avenue for NM-NC-based drug development for trypanosomiasis.

Single Mn Atom Doping in Chiral Sensitive Assembled Gold Clusters to Molecular Magnet.

Chiral stirred optical and magnetic properties, through the doping of assembled ultrasmall metal clusters (AMCs), are promising discernment to rivet the molecule-like quantum devices. Here, the single manganese (Mn) atom doping and assembly of the gold cluster (Au8), leading to the chirality driven magnetism, has been achieved through a ligand-mediated growth. The X-ray absorption near edge structure and electron paramagnetic resonance studies corroborate the tetrahedral coordinated local structure of Mn dopant in the Au host. The optical and vibrational circular dichroic analysis affirms the modulation of chirality (negative to positive) in the presence of the Mn. A distinct ferromagnetic hysteresis loop at 300 K shows Mn ridden chiral sensitive ferromagnetism in contrary to the ligand influenced superparamagnetic undoped AMCs. The spin-polarized density functional theory level of calculations reveal the partial overlapping of spin-up and -down density of states in the doped AMCs, attributing to the ferromagnetic nature as like a molecular magnet suitable for the opto-spintronics application.

One-Pot Synthesis of Ultra-Small Pt Dispersed on Hierarchical Zeolite Nanosheet Surfaces for Mild Hydrodeoxygenation of 4-Propylphenol

The rational design of ultra-small metal clusters dispersed on a solid is of crucial importance in modern nanotechnology and catalysis. In this contribution, the concept of catalyst fabrication with a very ultra-small size of platinum nanoparticles supported on a hierarchical zeolite surface via a one-pot hydrothermal system was demonstrated. Combining the zeolite gel with ethylenediaminetetraacetic acid (EDTA) as a ligand precursor during the crystallization process, it allows significant improvement of the metal dispersion on a zeolite support. To illustrate the beneficial effect of ultra-small metal nanoparticles on a hierarchical zeolite surface as a bifunctional catalyst, a very high catalytic performance of almost 100% of cycloalkane product yield can be achieved in the consecutive mild hydrodeoxygenation of 4-propylphenol, which is a lignin-derived model molecule. This instance opens up perspectives to improve the efficiency of a catalyst for the sustainable conversion of biomass-derived compounds to fuels.

Spectral Explanation for Statistical Odd-Even Staggering in Few Fermions Systems

Odd-even statistical staggering in a Lipkin-like few fermions model has been recently encountered. Of course, staggering in nuclear binding energies is a well established fact. Similar effects are detected in other finite fermion systems as well, as for example, ultra small metallic grains and metal clusters. We work in this effort with the above-mentioned Lipkin-like, two-level fermion model and show that statistical staggering effects can be detailedly explained by recourse to a straightforward analysis of the associated energy-spectra.

Pt Nanoparticles Confined by Zirconium Metal-Organic Frameworks with Enhanced Enzyme-like Activity for Glucose Detection.

Metal nanozymes hold promise for chemical and biological applications, and their implementation relies on high catalytic efficiency and stability. Using the metal–organic framework as an ideal carrier for well-dispersed ultra-small metal nanoparticles (NPs) is beneficial for improving the catalytic efficiency of nanozymes. In this study, a zirconium-based metal organic framework (UiO-66) with good chemical stability and high porosity was synthesized and used to construct Pt/UiO-66 nanocomposites. The percentage of Pt in UiO-66 can be tuned easily by adjusting the feeding amount of PtCl42–. Because of the confinement effect of mesopores, the Pt particles with an average diameter of 3.8 nm are formed and dispersed throughout the pores of the UiO-66 particle. The Pt/UiO-66 composites show efficient oxidase- and peroxidase-like activity. Both the oxidase- and peroxidase-like activities are dependent on the Pt percentage. Pt/UiO-66-6% exhibits enhanced peroxidase-like activity, ∼3.9 times higher than that of commercial Pt/C with 10 wt % Pt. We propose that the construction of Pt/UiO-66 increased the utilization efficiency and stability of Pt NPs and provided more active sites for catalytic reactions. Using the peroxidase-like activity of Pt/UiO-66, a colorimetric method that can be used for actual blood glucose detection was developed for the specific detection of glucose with a limit of detection of 0.033 mM.

High-Yield Synthesis of AIE-Type Au22(SG)18 Nanoclusters through Precursor Engineering and Its pH-Dependent Size Transformation

In recent years, ultrasmall metal nanoclusters (NCs) with aggregation-induced emission (AIE) characteristics have drawn enormous attention due to their strong photoluminescence (PL) and potential a...

Steering the Assembly and Disassembly of Active Pd Sites in Organometallic Networks for Electrocatalytic Performance and Organic Transformation

AbstractHierarchical bottom‐up structuring in nature provides inspiration for the construction of self‐assembled complex with advanced properties out of simple building blocks. However, the development of self‐standing assemblies of ultrasmall metal nanoparticles using redox ligands is still challenging. Here, a molecule‐confined reduction strategy to prepare robust self‐organized superstructures through metal–ligand interfacial interactions and hydrogen bonding is reported. High‐density and well‐separated Pd nanoparticles and single atoms are embedded within organometallic matrixes (Pd@eFc) via in situ reduction of the Pd precursor by redox‐active ligands. Furthermore, these metal–organic networks can be disassembled into fragments with highly dispersed Pd nanoparticles and single atoms by solvent mediation. Strikingly, Pd@eFc disassembly delivers excellent oxygen reduction performance, while its assembly can act as a selective hydrogenation catalyst. This viable molecule‐confined reduction strategy can also be applied to other organometallic superstructures (e.g., Au@eFc, Ag@eFc). The findings thus encourage on‐going study to explore controlled hierarchically self‐assembled superstructures for a wide range of catalysis.

Multiscale Assembly of [AgS4 ] Tetrahedrons into Hierarchical Ag-S Networks for Robust Photonic Water.

There is an urgent need to assemble ultrasmall metal chalcogenides (with atomic precision) into functional materials with the required anisotropy and uniformity, on a micro- or even macroscale. Here, a delicate yet simple chemistry is developed to produce a silver-sulfur network microplate with a high monodispersity in size and morphology. Spanning from the atomic, molecular, to nanometer, to micrometer scale, the key structural evolution of the obtained microplates includes 2D confinement growth, edge-sharing growth mode, and thermodynamically driven layer-by-layer stacking, all of which are derived from the [AgS4 ] tetrahedron unit. The key to such a high hierarchical, complex, and accurate assembly is the dense deprotonated ligand layer on the surface of the microplates, forming an infinite surface with high negative charge density. This feature operates at an orderly distance to allow further hierarchical self-assembly on the microscale to generate columnar assemblies composed of microplate components, thereby endowing the feature of the 1D photonic reflector to water (i.e., photonic water). The reflective color of the resulting photonic water is highly dependent on the thickness of the building blocks (i.e., silver-sulfur microplates), and the coexistent order and fluidity help to form robust photonic water.

A simple, rapid and scalable synthesis approach for ultra-small size transition metal selenides with efficient water oxidation performance

A simple, rapid and scalable microwave method for preparing ultra-small size transition metal selenides to boost water oxidation.

Assembly of USPIO/MOF nanoparticles with high proton relaxation rates for ultrasensitive magnetic resonance sensing

We develop a magnetic resonance sensor (MRS) based on the assembly of ultra-small superparamagnetic iron oxide (USPIO) nanoparticles and metal organic framework (MOF) materials, which have high T2 proton relaxation rates (r2).

Evaluation of ultrasmall coinage metal M13(dppe)6 M = Cu, Ag, and Au clusters. Bonding, structural and optical properties from relativistic DFT calculations.

Ultrasmall ligand-protected clusters are prototypical species for evaluating the variation at the bottom of the nanoscale range. Here we explored the ultrasmall gold-phosphine M13(dppe)6 cluster, as a prototypical framework to gain insights into the fundamental similarities and differences between Au, Ag, and Cu, in the 1-3 nm size range, via relativistic DFT calculations. Different charge states involving 8- and 10-cluster electron (ce) species with a 1S21P6 and 1S21P61D2 configuration, leading to structural modification in the Au species between Au13(dppm)65+ and Au13(dppm)63+, respectively. Furthermore, this structural distortion of the M13 core is found to occur to a lower degree for the calculated Ag and Cu counterparts. Interestingly, optical properties exhibit similar main patterns along with the series, inducing a blue-shift for silver and copper, in comparison to the gold parent cluster. For 10-ce species, the main features of 8-ce are retained with the appearance of several weak transitions in the range. The ligand-core interaction is enhanced for gold counterparts and decreased for lighter counterparts resulting in the Au > Cu > Ag trend for the interaction stabilization. Hence, the Ag and Cu counterparts of the Au13(dppm)6 cluster appear as useful alternatives, which can be further explored towards different cluster alternatives for building blocks for nanostructured materials.

Ultrasmall Pd and PtPd nanoparticles for highly efficient catalysis directed by predesigned Morchella-inspired encapsulation

Although bio-inspired designs for ultrasmall metal nanoparticles (NPs) are likely to play an important role in exploring future heterogeneous catalysis materials, synthesizing these structures while retaining surface activity and avoiding aggregation is challenging. Inspired by the Morchella with the spatially and well-organized porous structures, we proposed a biological strategy to yield NPs with ultrasmall and highly dispersed while maintaining high catalytic activity through surfactin self-assembly. Here, multifunctional Morchella-like biological pores (MBP) nanomaterials (~28 nm) with reduction and encapsulation has been synthesized by surfactin self-assembly, then, ultrasmall PtPd (~2.90 nm) and Pd NPs (~2.87 nm) with coordinated sizes and well-dispersed have been successfully reduced and encapsulated inside the MBP. Notably, the synthesis possesses distinct advantages such as mild reaction conditions, strong controllability, good biological compatibility, low-toxicity and environmental friendliness. The as-prepared MBP-encapsulated ultrasmall PtPd and Pd NPs (M@MBP NPs) exhibited excellent catalytic activity and toxicity resistance for the ethanol oxidation reaction (EOR) in KOH, due to the synergistic effect of MBP and ultrasmall metal NPs. The current density of PtPd@MBP and Pd@MBP NPs were 3.35 and 2.72 A mg−1, respectively. Such MBP synthesized and encapsulated nanoparticles open a new frontier for the design and preparation of NPs for various applications, such as catalysis, bioremediation and drug delivery.

Ultrasmall Bi nanoparticles confined in carbon nanosheets as highly active and durable catalysts for CO2 electroreduction

Developing high-efficient and durable electrocatalysts for CO2 electroreduction reaction (CO2RR) at high current density is attractive but still challenging. In this study, ultrasmall Bi nanoparticles confined in carbon nanosheets are successfully prepared by directly annealing of dipped carbon cloth. Benefited from the uniform distribution of the ultrasmall Bi nanoparticles and the in‐situ‐formed carbon nanosheets, the resultant self-supported electrocatalysts exhibit excellent CO2RR activity in a synergistic way. The optimized Bi-PVP/CC600 exhibits high formate faradaic efficiency of over 81 % at high current densities in a wide potential range. Impressively, high durability is also achieved for this binder-free electrode, with a remarkable high current density of 54 mA∙cm−2 for nearly 40 h. The high performance associated with this facile and potentially scalable synthetic method suggests the great application potential of ultrasmall Bi nanoparticles in CO2RR. The strategy developed herein is versatile and can be extended to prepare other high‐performance ultrasmall metal nanoparticles catalysts.

Observing antimicrobial process with traceable gold nanoclusters

Understanding the interaction of nanomaterials with biological systems has always been of high concern and interest. An emerging type of nanomaterials, ultrasmall metal nanoclusters (NCs, < 2 nm in size), are promising in this aspect due to their well-defined molecular formulae and structures, as well as unique physical and chemical properties that are distinctly different from their larger counterparts (metal nanoparticles). For example, metal NCs possess intrinsic strong luminescence, which can be used for real-time tracking of their interactions with biological systems. Herein, luminescent gold (Au) NCs were used as traceable antimicrobial agents to study their interactions with the bacteria and to further understand their underlining antimicrobial mechanism. It is shown for the first time that the Au NCs would first attach on the bacterial membrane, penetrate, and subsequently accumulate inside the bacteria. Thereafter, the internalized Au NCs would induce reactive oxygen species (ROS) generation and damage the bacterial membrane, resulting in the leakage of bacterial contents, which can finally kill the bacteria. Traceable Au NCs (or other metal NCs) provide a promising platform to study the antimicrobial mechanisms as well as other fundamentals on the interfacing of functional nanomaterials with the biological systems, further increasing their acceptance in various biomedical applications.

A straightforward method to prepare supported Au clusters by mechanochemistry and its application in photocatalysis

Reducing the metal particle size on semiconductor-based materials from a few nanometers down to well-dispersed clusters or single atoms has been demonstrated to be an effective strategy to enhance the photocatalytic performance. However, designing a simple and fast synthesis procedure has consistently been a challenge. In this work, gold clusters have been easily synthesized and dispersed onto TiO2 surface by one-step ball milling from TiO2 and gold acetate. The Au clusters strongly interact with TiO2 and the resulting material exhibits outstanding photocatalytic performances on the generation of hydrogen under UV and visible light, which double those obtained on conventional Au/TiO2 photocatalysts containing Au nanoparticles. We have studied the effect of various preparation parameters and characterized the samples by a variety of microscopic and spectroscopic techniques. The particular architecture accomplished by ball milling results in efficient charge separation, low charge transfer resistance and high photocurrent response. This mechanochemical method not only provides a facile and cost-effective alternative to the conventional methods of fabricating Au/TiO2 catalysts, but also opens a promising avenue for developing other ultrasmall metal clusters onto different supports.