Precise design of dual active-site catalysts for synergistic catalytic therapy of tumors.

A proven and promising method to improve the catalytic performance of single-atom catalysts through the interaction between bimetallic atoms to change the active surface sites or adjust the catalytic sites of reactants is reported. In this work, we used an iron-platinum bimetallic reagent as the metal source to precisely synthesise covalent organic framework-derived diatomic catalysts (FePt-DAC/NC). Benefiting from the coordination between the two metal atoms, the presence of Pt single atoms can successfully regulate Fe-N3 activity. FePt-DAC/NC exhibited a stronger ability to catalyze H2O2 to produce toxic hydroxyl radicals than Fe single-atom catalysts (Fe-SA/NC) to achieve chemodynamic therapy of tumors (the catalytic efficiency improved by 186.4%). At the same time, under the irradiation of an 808 nm laser, FePt-DAC/NC exhibited efficient photothermal conversion efficiency to achieve photothermal therapy of tumors. Both in vitro and in vivo results indicate that FePt-DAC/NC can efficiently suppress tumor cell growth by a synergistic therapeutic effect with photothermally augmented nanocatalytic therapy. This novel bimetallic dual active-site monodisperse catalyst provides an important example for the application of single-atom catalysts in the biomedical field, highlighting its promising clinical potential.

Synthesizing Photoluminescent Au28 (SCH2 Ph-t Bu)22 Nanoclusters with Structural Features by Using a Combined Method.

We present a method for atomically precise nanocluster synthesis. As an illustration, we introduced the reducing-ligand induction combined method and synthesized a novel nanocluster, which was determined to be Au28 (SCH2 Ph-t Bu)22 with the same number of gold atoms as existing Au28 (SR)20 nanoclusters but different ligands (hetero-composition-homo-size). Compared with the latter, the former has distinct properties and structures. In particular, a novel kernel evolution pattern is reported, i.e., the quasi-linear growth of Au4 -tetrahedron by sharing one vertex and structural features, including a tritetrahedron kernel with two bridging thiolates and two Au6 (SCH2 Ph-t Bu)6 hexamer chair-like rings on the kernel surface were also first reported, which endow Au28 (SCH2 Ph-t Bu)22 with the best photoluminescence quantum yield among hydrophobic thiolated gold nanoclusters so far, probably due to the enhanced charge transfer from the bi-ring to the kernel via Au-Au bonds.

Compression-Driven Internanocluster Reaction for Synthesis of Unconventional Gold Nanoclusters.

Can 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 (SC2 H4 Ph)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.

Unravelling the Structure of a Medium-Sized Metalloid Gold Nanocluster and its Filming Property.

Unravelling the structure of thiolated metalloid gold nanoclusters in the medium-sized range by single crystal X-ray crystallography (SCXC) is challenging. Herein, we successfully synthesized a novel Au67 (SR)35 nanocluster, and unravelled its single crystal structure by SCXC, which features a mix-structured Au48 kernel protected by one Au4 (SR)5 staple and fifteen Au(SR)2 staples. Unprecedentedly, this structure can be thermally induced to aggregate into larger nanoparticles and self-deposit to form a gold nanoparticles film onto the walls of a vial or other substrates such as quartz, mica or ceramic, which can be developed into a facile, substrate-universal and scalable filming method. The film exhibits high sensitivity, uniformity and recyclability as a surface-enhanced Raman scattering (SERS) substrate and can be applied for detecting multiple organic pollutants.

Traceless Removal of Two Kernel Atoms in a Gold Nanocluster and Its Impact on Photoluminescence.

Removing or adding kernel atoms of metal nanoclusters (NCs) without leaving a trace is a substantial challenge because the kernel atoms are inside and covered by the outer staples. However, such kernel tuning is very important for improving the properties and acquiring an in-depth understanding of the kernel-property correlation. Photoluminescence (PL) is one of the most intriguing characteristics of metal NCs but has not been well understood until now. Inspired by these challenges/questions, we conducted this study and, for the first time, achieved the traceless removal of two kernel atoms in a gold nanocluster by applying a simple thermal treatment and revealed its impact on PL. Further, we demonstrated that the kernel Au-Au bond length can be an indicator for a comparison of the PL or kernel charge state between nanoclusters with similar kernel structures and sizes.

Distance makes a difference in crystalline photoluminescence.

Crystallization-induced photoluminescence weakening was recently revealed in ultrasmall metal nanoparticles. However, the fundamentals of the phenomenon are not understood yet. By obtaining conformational isomer crystals of gold nanoclusters, we investigate crystallization-induced photoluminescence weakening and reveal that the shortening of interparticle distance decreases photoluminescence, which is further supported by high-pressure photoluminescence experiments. To interpret this, we propose a distance-dependent non-radiative transfer model of excitation electrons and support it with additional theoretical and experimental results. This model can also explain both aggregation-induced quenching and aggregation-induced emission phenomena. This work improves our understanding of aggregated-state photoluminescence, contributes to the concept of conformational isomerism in nanoclusters, and demonstrates the utility of high pressure studies in nanochemistry.

A Dual Purpose Strategy to Endow Gold Nanoclusters with Both Catalysis Activity and Water Solubility.

Gold nanoclusters have attracted extensive interest for catalysis applications in recent years due to their ultrasmall sizes and well-defined compositions and structures. However, at least two challenges exist in this emerging field. First, the steric hindrance of the ligands inhibits the catalysis activity, and second, the mechanism underlying water-phase catalysis using gold nanoclusters is often ambiguous. Herein, we introduce a "kill two birds with one stone" strategy to address these two challenges via the use of host-guest chemistry. As an illustration, a novel adamantanethiolate-protected Au40(S-Adm)22 nanocluster was synthesized, bound with γ-CD-MOF, and then transferred to the HRP-mimicking reaction system. The as-obtained catalyst exhibits excellent water solubility and catalytical activity, totally different from the virgin Au40(S-Adm)22 nanoclusters. Further, the detailed HRP-mimicking catalysis mechanism was proposed and supported by DFT calculation. Another interesting finding is the unique structure of Au40(S-Adm)22, which can be regarded as an Au13 icosahedron unit derived structure but different from the widely reported icosahedron contained nanocluster where the Au13 icosahedrons are often centered. These novel, intriguing results have important implication for the property tuning and practical application of metal nanoclusters in the future.

Alternating Array Stacking of Ag26 Au and Ag24 Au Nanoclusters.

An assembly strategy for metal nanoclusters using electrostatic interactions with weak interactions, such as C-H⋅⋅⋅π and π⋅⋅⋅π interactions in which cationic [Ag26 Au(2-EBT)18 (PPh3 )6 ]+ and anionic [Ag24 Au(2-EBT)18 ]- nanoclusters gather and assemble in an unusual alternating array stacking structure is presented. [Ag26 Au(2-EBT)18 (PPh3 )6 ]+ [Ag24 Au(2-EBT)18 ]- is a new compound type, a double nanocluster ion compound (DNIC). A single nanocluster ion compound (SNIC) [PPh4 ]+ [Ag24 Au(2-EBT)18 ]- was also synthesized, having a k-vector-differential crystallographic arrangement. [PPh4 ]+ [Ag24 Au(2,4-DMBT)18 ]- adopts a different assembly mode from both [Ag26 Au(2-EBT)18 (PPh3 )6 ]+ [Ag24 Au(2-EBT)18 ]- and [PPh4 ]+ [Ag24 Au(2-EBT)18 ]- . Thus, the striking packing differences of [Ag26 Au(2-EBT)18 (PPh3 )6 ]+ [Ag24 Au(2-EBT)18 ]- , [PPh4 ]+ [Ag24 Au(2-EBT)18 ]- and the existing [PPh4 ]+ [Ag24 Au(2,4-DMBT)18 ]- from each other indicate the notable influence of ligands and counterions on the self-assembly of nanoclusters.

Fcc versus Non-fcc Structural Isomerism of Gold Nanoparticles with Kernel Atom Packing Dependent Photoluminescence.

Structural isomerism allows the correlation between structures and properties to be investigated. Unfortunately, the structural isomers of metal nanoparticles are rare and genuine structural isomerism with distinctly different kernel atom packing (e.g., face-centered cubic (fcc) vs. non-fcc) has not been reported until now. Herein we introduce a novel ion-induction method to synthesize a unique gold nanocluster with a twist mirror symmetry structure. The as-synthesized nanocluster has the same composition but different kernel atom packing to an existing gold nanocluster Au42 (TBBT)26 (TBBT=4-tert-butylbenzenethiolate). The fcc-structured Au42 (TBBT)26 nanocluster shows more enhanced photoluminescence than the non-fcc-structured Au42 (TBBT)26 nanocluster, indicating that the fcc-structure is more beneficial for emission than the non-fcc structure. This idea was supported by comparison of the emission intensity of another three pairs of gold nanoclusters with similar compositions and sizes but with different kernel atom packings (fcc vs. non-fcc).

Discovery, Mechanism, and Application of Antigalvanic Reaction.

Among many outstanding findings associated with the quantum size effect, one of the most exciting is the discovery of the antigalvanic reaction (AGR), which is the opposite of the classic galvanic reaction (GR) that has a history of nearly 240 years. The GR, named after Italian scientist Luigi Galvani, involves the spontaneous reduction of a noble-metal cation by a less noble metal in solution driven by the difference in electrochemical potentials. Classic galvanic reduction has been widely applied and has recently received particular interest in nanoscience and nanotechnology. However, the opposite of GR, that is, reduction of metal ions by less reactive (or more noble) metals, has long been regarded as a virtual impossibility until the recent surprising findings regarding atomically precise ultrasmall metal nanoparticles (nanoclusters), which bridge the gap between metal atoms (complexes) and metal nanocrystals and provide opportunities for novel scientific findings due to their well-defined compositions and structures. The AGR is significant not only because it is the opposite of the classic galvanic theory but also because it opens extensive applications in a large range of fields, such as sensing and tuning the compositions, structures, and properties of nanostructures that are otherwise difficult to obtain. Starting with the proposal of the general AGR concept in 2012 by Wu, a new era began, in which AGR received widespread attention and was extensively studied. After years of effort, great advances have been achieved in the research on AGR, which will be reviewed below. In this Account, we first provide a short introduction to the AGR concept and then discuss the driving force of the AGR together with the effecting factors, including the ligand, particle size, solvent, metal ion precursor, and ion dose. Subsequently, the application of the AGR in engineering atomically precise alloy (bimetallic and trimetallic) and monometallic nanoclusters is described, and tuning the properties of the parent nanoclusters is also included. In particular, four alloying modes (namely, (i) addition, (ii) replacement, (iii) replacement and structural transformation, and (iv) nonreplacement and structural transformation) associated with the AGR are discussed. After that, the applications of the AGR in metal ion sensing and antioxidation are reviewed. Finally, future prospects are discussed, and some challenging issues are presented at the end of this Account. It is expected that this Account will stimulate more scientific and technological interests in the AGR, and exciting progress in the understanding and application of the AGR will be made in the coming years.

Kernel Homology in Gold Nanoclusters.

Homology is well known in organic chemistry; however, it has not yet been reported in nanochemistry. Herein, we introduce the concept of kernel homology to describe the phenomenon of metal nanoclusters sharing the same "functional group" in kernels with some similar properties. To illustrate this point, we synthesized two novel gold nanoclusters, Au44 (TBBT)26 and Au48 (TBBT)28 (TBBTH=4-tert-butylbenzenethiol), and solved their total structures by X-ray crystallography, which reveals that they have the same Au23 bi-icosahedron capped with a similar bottom cap (Au6 and Au8 , respectively) in the kernels. The two novel gold nanoclusters, together with the existing Au38 (PET)24 nanocluster (PETH=phenylethanethiol), have the same "functional group"-Au23 -in their kernels and have some similar properties (e.g., electrochemical properties); therefore, they are comparable to the homologues in organic chemistry.

Kernel Tuning and Nonuniform Influence on Optical and Electrochemical Gaps of Bimetal Nanoclusters.

Fine tuning nanoparticles with atomic precision is exciting and challenging and is critical for tuning the properties, understanding the structure-property correlation and determining the practical applications of nanoparticles. Some ultrasmall thiolated metal nanoparticles (metal nanoclusters) have been shown to be precisely doped, and even the protecting staple metal atom could be precisely reduced. However, the precise addition or reduction of the kernel atom while the other metal atoms in the nanocluster remain the same has not been successful until now, to the best of our knowledge. Here, by carefully selecting the protecting ligand with adequate steric hindrance, we synthesized a novel nanocluster in which the kernel can be regarded as that formed by the addition of two silver atoms to both ends of the Pt@Ag12 icosohedral kernel of the Ag24Pt(SR)18 (SR: thiolate) nanocluster, as revealed by single crystal X-ray crystallography. Interestingly, compared with the previously reported Ag24Pt(SR)18 nanocluster, the as-obtained novel bimetal nanocluster exhibits a similar absorption but a different electrochemical gap. One possible explanation for this result is that the kernel tuning does not essentially change the electronic structure, but obviously influences the charge on the Pt@Ag12 kernel, as demonstrated by natural population analysis, thus possibly resulting in the large electrochemical gap difference between the two nanoclusters. This work not only provides a novel strategy to tune metal nanoclusters but also reveals that the kernel change does not necessarily alter the optical and electrochemical gaps in a uniform manner, which has important implications for the structure-property correlation of nanoparticles.

Surface Single-Atom Tailoring of a Gold Nanoparticle.

Surface single-atom tailoring of a gold nanoparticle, that is, adding, removing, or replacing one surface atom on a structure-resolved nanoparticle in a controlled manner, is very exciting yet challenging and has not been hitherto achieved. Herein we report the first realization of the introduction of a single sulfur atom onto the surface of the structure-unraveled Au60S6(SCH2Ph)36 nanoparticle. Single-crystal X-ray crystallography reveals that the as-obtained nanoparticle consists of one Au17 kernel protected by one Au20S3(SCH2Ph)18 and one unprecedented Au23S4(SCH2Ph)18 motif with the introduced sulfur atom included as a tetrahedral-coordinated µ4-S. The introduced sulfur leads to the changes of both internal structure and crystallographic arrangement. Unlike the case of 6HLH arrangement in Au60S6(SCH2Ph)36 crystals, the "ABAB" arrangement in Au60S7(SCH2Ph)36 crystals enhances the solid photoluminescence of amorphous Au60S7(SCH2Ph)36 and brings a slight redshift of the maximum emission. The extensive near-infrared emission provides Au60S7(SCH2Ph)36 potential applications in some fields such as anticounterfeiting, imaging, etc.

The reactivity of phenylethanethiolated gold nanoparticles with acetic acid.

We report the size-dependent reactivity of phenylethanethiolated gold nanoparticles with acetic acid. Employing this reactivity, we synthesize a novel nanocluster Au38(PET)26 (PET: phenylethanethiolate), which is otherwise difficult to obtain and exhibits remarkably different photoluminescence and electrochemical properties compared with the well-known Au38(PET)24 nanoclusters. And the reaction process between Au38(PET)26 and acetic acid was probed by matrix-assisted laser desorption/ionization time of flight mass spectrometry.

The fourth crystallographic closest packing unveiled in the gold nanocluster crystal.

Metal nanoclusters have recently attracted extensive interest not only for fundamental scientific research, but also for practical applications. For fundamental scientific research, it is of major importance to explore the internal structure and crystallographic arrangement. Herein, we synthesize a gold nanocluster whose composition is determined to be Au60S6(SCH2Ph)36 by using electrospray ionization mass spectrometry and single crystal X-ray crystallography (SCXC). SCXC also reveals that Au60S6(SCH2Ph)36 consists of a fcc-like Au20 kernel protected by a pair of giant Au20S3(SCH2Ph)18 staple motifs, which contain 6 tetrahedral-coordinate µ4-S atoms not previously reported in the Au-S interface. Importantly, the fourth crystallographic closest-packed pattern, termed 6H left-handed helical (6HLH) arrangement, which results in the distinct loss of solid photoluminescence of amorphous Au60S6(SCH2Ph)36, is found in the crystals of Au60S6(SCH2Ph)36. The solvent-polarity-dependent solution photoluminescence is also demonstrated. Overall, this work provides important insights about the structure, Au-S bonding and solid photoluminescence of gold nanoclusters.

Fluorescent Gold Nanoclusters with Interlocked Staples and a Fully Thiolate-Bound Kernel.

The structural features that render gold nanoclusters intrinsically fluorescent are currently not well understood. To address this issue, highly fluorescent gold nanoclusters have to be synthesized, and their structures must be determined. We herein report the synthesis of three fluorescent Au24 (SR)20 nanoclusters (R=C2 H4 Ph, CH2 Ph, or CH2 C6 H4 (t) Bu). According to UV/Vis/NIR, differential pulse voltammetry (DPV), and X-ray absorption fine structure (XAFS) analysis, these three nanoclusters adopt similar structures that feature a bi-tetrahedral Au8 kernel protected by four tetrameric Au4 (SR)5 motifs. At least two structural features are responsible for the unusual fluorescence of the Au24 (SR)20 nanoclusters: Two pairs of interlocked Au4 (SR)5 staples reduce the vibration loss, and the interactions between the kernel and the thiolate motifs enhance electron transfer from the ligand to the kernel moiety through the Au-S bonds, thereby enhancing the fluorescence. This work provides some clarification of the structure-fluorescence relationship of such clusters.

Synthesis of fluorescent phenylethanethiolated gold nanoclusters via pseudo-AGR method.

It is well known that the fluorescence of metal nanoclusters is strongly dependent of the protecting ligand and reports of phenylethanethiolated metal nanoclusters with distinct fluorescence are rare. Herein, a fluorescent phenylethanethiolated gold nanocluster is synthesized using an unexpected pseudo-AGR method (AGR: anti-galvanic reduction). The cluster is precisely determined to be Au24(SC2H4Ph)20 by isotope-resolved mass spectroscopy in tandem with thermogravimetric analysis (TGA). The fluorescence comparison between Au24(SC2H4Ph)20, Au25(SC2H4Ph)18, Au38(SC2H4Ph)24 and Au144(SC2H4Ph)60 is also presented. The finding of the fluorescent phenylethanethiolated gold nanocluster in this work has important implication for future study on the fluorescence of metal nanoclusters.

Controlled synthesis of Au-Fe3O4 hybrid hollow spheres with excellent SERS activity and catalytic properties.

Au-Fe3O4 hybrid hollow spheres have been successfully synthesized by a one-pot process via the hydrothermal treatment of FeCl3, HAuCl4, citrate, urea, and polyacrylamide (PAM). The amount of Au nanoparticles located in the hybrid hollow spheres can be tuned by changing the molar ratio of Au/Fe precursors. A possible synthetic mechanism of the Au-Fe3O4 hybrid hollow spheres has been proposed. The obtained hybrids exhibit not only a superior surface-enhanced Raman scattering (SERS) sensitivity, but also an excellent catalytic activity. The detection limit of the Au-Fe3O4 hybrid hollow spheres (the Au/Fe molar ratio is 0.2, Au-Fe3O4-0.2) for R6G can reach up to 10(-10) M, which can meet the required concentration level for ultratrace detection of analytes using SERS. Furthermore, the catalytic experiments of the Au-Fe3O4-0.2 hybrid hollow spheres demonstrate that the model of 4-nitrophenol (4-NP) molecules can be degraded within 3 min and the catalytic activity can be recovered without sharp activity loss in six runs, which indicates their superior catalytic degradation activity. The reason may be due to the highly efficient partial charge transfer between Au and Fe3O4 at the nanoscale interface. The results indicate that the bifunctional Au-Fe3O4 hybrid hollow spheres can serve as promising materials in trace detection and industrial waste water treatment.

Controlled synthesis of Au-loaded Fe3O4@C composite microspheres with superior SERS detection and catalytic degradation abilities for organic dyes.

Bifunctional Au-loaded Fe3O4@C composite microspheres were controllably synthesized by coating of Au nanoparticles (NPs) on the surface of the poly(diallyldimethylammonium chloride) (PDDA) functionalized Fe3O4@C microspheres. The amount of Au loading can be effectively tuned by altering the feeding amounts of solution Au NPs or further growth. The obtained Au-loaded Fe3O4@C composite microspheres exhibit both superior surface-enhanced Raman scattering (SERS) sensitivity and catalytic degradation activity for organic dyes. The SERS signal intensity of methylene blue (MB) distinctly enhances with the increase of Au loading, which endows increased Raman 'hot spots' and provides a significant enhancement of the Raman signal through electromagnetic (EM) field enhancements. Furthermore, the catalytic experiments of the Fe3O4@C@Au composite microspheres with the highest Au loading demonstrate that the model organic dye of MB molecules could be degraded within 10 min and the catalytic activity could be recovered without sharp activity loss in six runs, which indicates their superior catalytic degradation activity. The reason could be mainly ascribed to the synergistic effects of small size of Au NPs, the good adsorption behavior of carbon layers and the excellent dispersivity of the composite microspheres induced by the sandwiched carbon layers. The results indicate that the bifunctional Au-loaded Fe3O4@C composite microspheres could be served as promising materials in wastewater treatment.

A simple and highly efficient route to the synthesis of NaLnF4-Ag hybrid nanorice with excellent SERS performances.

This paper reports the synthesis of a new class of NaLnF(4)-Ag (Ln = Nd, Sm, Eu, Tb, Ho) hybrid nanorice and its application as a surface-enhanced Raman scattering (SERS) substrate in chemical analyses. Rice-shaped NaLnF(4) nanoparticles as templates are prepared by a modified hydrothermal method. Then, the NaLnF(4) nanorice particles are decorated with Ag nanoparticles by magnetron sputtering method to form NaLnF(4)-Ag hybrid nanostructures. The high-density Ag nanogaps on NaLnF(4) can be obtained by the prolonging sputtering times or increasing the sputtering powers. These nanogaps can serve as Raman 'hot spots', leading to dramatic enhancement of the Raman signal. The NaLnF(4)-Ag hybrid nanorice is found to be robust and is an efficient SERS substrate for the vibrational spectroscopic characterization of molecular adsorbates; the Raman enhancement factor of Rhodamine 6G (R6G) absorbed on NaLnF(4)-Ag nanorice is estimated to be about 10(13). Since the produced NaLnF(4)-Ag hybrid nanorice particles are firmly fastened on a silicon wafer, they can serve as universal SERS substrates to detect target analytes. We also evaluate their SERS performances using 4-mercaptopyridine (Mpy), and 4-mercaptobenzoic acid (MBA) molecules, and the detection limit for Mpy and MBA is as low as 10(-12) M and 10(-10) M, respectively, which meets the requirements of the ultratrace detection of analytes. This simple and highly efficient approach to the large-scale synthesis of NaLnF(4)-Ag nanorice with high SERS activity and sensitivity makes it a perfect choice for practical SERS detection applications.