Synthesis Of Metal Nanoclusters Research Articles

A Mini Review on Surface-Enhanced Raman Scattering based Nanoclusters for Sensing and Imaging Applications

Background: The invention of enhanced Raman scattering by adsorbing molecules on nanostructured metal surfaces is a milestone in the development of spectroscopic and analytical techniques. Important experimental and theoretical efforts were geared towards understanding the Surface Enhanced Raman Scattering effect (SERS) and evaluating its significance in a wide range of fields in different types of ultrasensitive sensing applications. Methods: Metal nanoclusters have been widely studied due to their unique structure and individual properties, which place them among single metal atoms and larger nanoparticles. In general, the nanoparticles with a size less than 2 nm is defined as nanoclusters (NCs) and they possess distinct optical properties. In addition, the excited electrons from absorption bands results in the emission of positive luminescence associated to the quantum size effect in which separate energy levels are produced. Results: It is demonstrated that fluorescent based SERS investigations of metal nanoparticles have showed more photostability, high compatibility, and good water solubility, has resulted in high sensitivity, better imaging and sensing experience in the biomedical applications. Conclusion: In the present review, we report recent trends in the synthesis of metal nanoclusters and their applications in biosensing and bio-imaging applications due some benefits including cost-effectiveness, easy synthesis routes and less consumption of sample volumes. Outcomes of this study confirms that SERS based fluorescent nanoclusters could be one of thrust research areas in biochemistry and biomedical engineering.

Chirality Induction in the Synthesis of Ag29 Nanoclusters with Asymmetric Structure

Surface ligands play a critical role in the synthesis of metal nanoclusters (NCs) tuning the sizes, compositions, structures, and properties at the atomic level. Chiral ligands often lead to the fo...

Effect of Nobel Metal Ions on the Synthesis of Metal Nanoclusters for Selective Detection of Various Heavy Metals

In this study, effect of noble metal ion (Au, Ag and Cu) on the synthesis of metal nanoclusters (MNCs) has been investigated. Through heating at 70ºC, TSA/BSA-Au, -Ag and -Cu NCs were separately prepared from Au3+, Ag+, and Cu2+in the presence of bovine serum albumin (BSA) and thiosalicylic acid (TSA). They exhibit photoluminescence (PL) at 700, 624 and 430 nm, with average life times of 1500, 100 and 11.71 ns, respectively, when excited at 350 nm. X–ray photoelectron spectroscopy (XPS) data support the presence of metal core (M0) and metal–thiolate shell (Mn–SRm), each in the TSA/BSA-MNCs. Spectroscopic measurements reveal the formation of Au32–SR, Ag9–SR and (Cu4–Cu13)–SR species separately in the TSA/BSA-Au, -Ag and -Cu NCs. Through PL quenching of the TSA/BSA-Au, -Ag and -Cu NCs, they have been used separately for quantitation of Hg2+, As3+and Cr6+ , with linear ranges of 10-400, 4-18, and 40-400 nM and limits of detection (LODs) of 0.25, 2.34 and 3.54 nM, respectively. The PL quenching is mainly due to aggregation of the MNCs through metallophilic or metal–thiol complexation. The stable TSA/BSA–Au, -Ag and -Cu NCs have been employed separately for the determination of the concentrations of Hg2+, As3+and Cr6+ions in the spiked sea water samples, showing advantages of simplicity, rapidity, high selectivity, and sensitivity.

Engineering Fluorescent Gold Nanoclusters Using Xanthate-Functionalized Hydrophilic Polymers: Toward Enhanced Monodispersity and Stability.

We introduce xanthate-functionalized poly(cyclic imino ethers)s (PCIEs), specifically poly(2-ethyl-2-oxazoline) and poly(2-ethyl-2-oxazine) given their stealth characteristics, as an attractive alternative to conventional thiol-based ligands for the synthesis of highly monodisperse and fluorescent gold nanoclusters (AuNCs). The xanthate in the PCIEs interacts with Au ions, acting as a well-controlled template for the direct formation of PCIE-AuNCs. This method yields red-emitting AuNCs with a narrow emission peak (λem = 645 nm), good quantum yield (4.3-4.8%), long fluorescence decay time (∼722-844 ns), and unprecedented product yield (>98%). The PCIE-AuNCs exhibit long-term colloidal stability, biocompatibility, and antifouling properties, enabling a prolonged blood circulation, lower nonspecific accumulation in major organs, and better renal clearance when compared with AuNCs without polymer coating. The advances made here in the synthesis of metal nanoclusters using xanthate-functionalized PCIEs could propel the production of highly monodisperse, biocompatible, and renally clearable nanoprobes in large-scale for different theranostic applications.

Effect of Nobel Metal Ions on the Synthesis of Metal Nanoclusters for Selective Detetction of Various Heavy Metals

In this study, effect of noble metal ion (Au, Ag and Cu) on the synthesis of metal nanoclusters (MNCs) has been investigated. Through heating at 70ºC, TSA/BSA-Au, -Ag and -Cu NCs were separately prepared from Au3+, Ag+and Cu2+in the presence of bovine serum albumin (BSA) and thiosalicylic acid (TSA). They exhibit photoluminescence (PL) at 700, 624 and 430 nm,with average life times of 1500, 100 and 11.71 ns,respectively, when excited at 350 nm. X–ray photoelectronspectroscopy (XPS) data support the presence of metal core (M0) and metal–thiolate shell (Mn–SRm), each in the TSA/BSA-MNCs. Spectroscopic measurements reveal the formation of Au32–SR, Ag9–SR and (Cu4–Cu13)–SR species separately in the TSA/BSA-Au, -Ag and -Cu NCs. Through PL quenching of the TSA/BSA-Au, -Ag and -Cu NCs, they have been used separately for quantitation of Hg2+, As3+and Cr6+ , with linear rangesof 10-400, 4-18, and 40-400 nM and limits of detection (LODs) of 0.25, 2.34 and 3.54 nM, respectively. The PL quenching is mainly due to aggregationof the MNCs through metallophilic or metal–thiol complexation.The stable TSA/BSA–Au, -Ag and -Cu NCs have been employed separately for the determination of the concentrations of Hg2+, As3+and Cr6+ions in the spiked sea water samples, showing advantages of simplicity, rapidity, high selectivity, and sensitivity.

Oxometalate and phosphine ligand co-protected silver nanoclusters: Ag28(dppb)6(MO4)4 and Ag32(dppb)12(MO4)4(NO3)4.

Thiols, alkynyls and phosphines are the most widely used organic ligands to attain atomically precise metal nanoclusters, while oxometalates as inorganic ligands have almost been neglected in this field. Here, we used oxometalates (e.g., MoO42- and WO42-) as protecting ligands along with phosphines, such as 1,4-bis(diphenylphosphino)butane (dppb), to design and synthesize a new class of silver nanoclusters including Ag28(dppb)6(MoO4)4, Ag28(dppb)6(WO4)4 and Ag32(dppb)12(MoO4)4(NO3)4. Each cluster consists of a two-shell Ag4@Ag24 core protected by 4 oxometalates. These clusters exhibit similar optical absorption and photoluminescence properties that are not dependent on surface ligands. Furthermore, the electronic structure analysis shows that the clusters are 20-electron "superatoms". This work demonstrates that oxometalates can play a key role in the formation of silver nanoclusters, and the effect of oxometalates should be considered in the design and synthesis of metal nanoclusters.

Surface Chemistry of Atomically Precise Coinage-Metal Nanoclusters: From Structural Control to Surface Reactivity and Catalysis.

A comprehensive understanding of chemical bonding and reactions at the surface of nanomaterials is of great importance in the rational design of their functional properties and applications. With the rapid development in cluster science, it has become clear that atomically precise metal clusters represent ideal models for resolving various important and/or unsolved issues related to surface science. This Account highlights our recent efforts on the fabrication of ligand-stabilized coinage nanoclusters with atomic precision from the viewpoint ofsurface coordination chemistry in particular. The successful synthesis of a large variety of metal clusters in our group has greatly benefitted from the development of an effective amine-assisted NaBH4 reduction method. First discussed in this Account is how the introduction of amines in the synthetic protocol enhances the long-term stability and high-yield production of Ag/Cu-based metals in air. Such a method allows the utilization of different organic ligands as surface stabilizing agents to manipulate both the core and surface structures of metal nanoclusters, helping to understand the role of surface ligands in determining the structures of metal nanoclusters. The coordination chemistry of ligands used in the synthesis of metal nanoclusters is crucial in determining their overall shape, metal arrangement, surface ligand binding structure, chirality and also metal exposure. Detailed discussions are given in the following four different systems: (1) The co-use of phosphines and thiolates with rich coordination structures (2 to 4-coordinated) helps to control the formation of a sequence of Ag nanoclusters with a near-perfectly cubic shape; (2) The metal arrangements and surface structures of AuCu clusters highly depend on metal precursors and counter cations used in the synthesis; (3) Metal clusters with intrinsic chirality are readily prepared by introducing chiral ligands or counterions, making it possible to obtain optically active enantiomers and understand the origin of chirality of metal nanoclusters; (4) The variation of metal exposure of the inner metal core of metal nanocluster can be controlled by the surface ligand coordination structure. Such capabilities to manipulate the surface structure of metal nanoclusters allow the creation of model systems for investigating the structure-reactivity relationship of metal nanomaterials. Several important examples are then discussed to highlight the importance of ligand coordination chemistry in tuning the surface reactivity and catalysis of metal nanoclusters. For example, bulky thiolates on Agare demonstrated to be more labile than small thiolates for making metal nanoclusters with both enhanced ligand exchange capability and catalysis. Alkynyl ligands can be thermally released from metal nanoclusters more easily than thiolates and halides while maintaining the overall structure, thereby serving as ideal systems for understanding the promoting effect of surface stabilizers on catalysis. Finally, we provide a perspective on the principles of surface coordination chemistry of metal nanoclusters and their potential applications with regards to catalysis of protected metal clusters.

Evolution of thiolate-stabilized Ag nanoclusters from Ag-thiolate cluster intermediates

The synthesis of atomically precise thiolate-stabilized silver (Ag) nanoclusters is the subject of intense research interest, yet the formation mechanism of such nanoclusters remains obscure. Here, electrospray ionization mass spectrometry is successfully applied to monitor the reaction intermediates formed during the sodium-borohydride-reduction of silver 4-tert-butylbenzenethiolate (AgSPh-tBu). We demonstrate a unique evolution route to thiolate-stabilized Ag nanoclusters mediated by Ag-thiolate clusters. The Ag-thiolate clusters form in the initial stage of reduction contain tens of Ag atoms and similar number of ligands, and they are transformed into Ag17(SPh-tBu)123− and Ag44(SPh-tBu)304− nanoclusters in the later reduction process. The number of Ag atoms in the Ag-thiolate clusters determines the reaction path to each final nanocluster product. A similar mechanism is found when silver 2,4-dimethylbenzenethiolate (AgSPhMe2) is used as precursor. This mechanism differs markedly from the long-established bottom-up evolution process, providing valuable new insights into the synthesis of metal nanoclusters.

Monolayer‐Protected Clusters: Versatile Materials of Electrochemical Importance

Monolayer‐Protected Clusters: Versatile Materials of Electrochemical Importance

Chloride-Promoted Formation of a Bimetallic Nanocluster Au80Ag30 and the Total Structure Determination.

We report the total structure determination of a large bimetallic nanocluster with an overall composition of [Au80Ag30(C≡CPh)42Cl9]Cl. It is the largest structurally characterized bimetallic coinage nanocluster so far. The 110 metal atoms are distributed in a concentric four-shell Russian doll arrangement, Au6@Au35@Ag30Au18@Au21. There are 42 PhC≡C- ligands and 9 μ2-chloride ligands clamping on the cluster surface. The chloride is proven to be critical for the formation of this giant cluster, as the control experiment in the absence of halide gives only smaller species. This work demonstrates that the halide can play a key role in the formation of a large metal nanocluster, and the halide effect should be considered in the design and synthesis of metal nanoclusters.

Evolution of the structure and magneto-optical properties of ion beam synthesized iron nanoclusters

Changes in the structural, magnetic, and optical properties are observed during the synthesis of metallic nanoclusters fabricated on the surface of a thin silica layer by ion beam implantation of iron atoms. Iron atoms were implanted to the fluence of 1016 cm−2. The ion implantation depth in 400-nm thick SiO2 film on a Si (100) substrate was 25 nm. The implanted samples were subsequently annealed for periods of seconds to hours at 1000 °C with Electron Beam Annealing. Ellipsometry and Rutherford Backscattering Spectrometry spectra were fitted with appropriate models to retrieve the optical characteristics, composition, and structure of the samples. Magneto Optical Kerr Effect measurements and SQUID magnetometry were performed to investigate the effect of the structural changes identified by TEM measurements on the superparamagnetic and magneto-optical properties of the samples during the annealing process. The changes in the Fe crystalline(core)/amorphous oxide(shell) structure and the position of the nanoclusters relative to the surface observed for small annealing durations are shown to enhance the Kerr effect resulting into high coercive field and high amplitude in the Kerr rotation and ellipticity.

Nanocluster Nucleation and Growth in Polymeric Media Below the Glass Transition

The synthesis of metal nanoclusters in a polymeric environment has been shown to yield nearly monodisperse particles, whose size is controlled by the strength of the polymer/metal interactions. Although the phenomenon is quite general, little is known regarding the mechanism by which the polymer controls nanocluster size. Previous studies of the kinetics of nanocluster growth in polymeric melts above the glass transition temperature (Tg) suggest that the nanoparticle size is set by the critical cluster size (nucleation stage) rather than the rate of metal precursor transport, namely, growth. In this paper, we examine the kinetics of iron oxide (Fe2O3) nanocluster formation below the glass temperature (Tg) in two polymer melts: polystyrene (PS) and poly(methyl methacrylate) (PMMA). We find that the morphology of the nanoclusters formed below Tg is highly sensitive to the system temperature and differs significantly from the morphology above Tg. However, the kinetics of cluster formation is exponential with time in both PS and PMMA, both above and below Tg. The glass transition does not significantly affect the rate constant in PS, thereby suggesting that the cluster formation mechanism is largely insensitive to the polymer state (glassy or melt). However, we find a significant difference in in the kinetics of PMMA above (where the rate constant increases exponentially with T) and below (where it is nearly constant) the Tg.

Effect of polymer architecture on metal nanoclusters

Synthesis of metal nanoclusters in polymeric media has been shown to yield small clusters with a narrow size distribution. Embedding such clusters in the three-dimensional structures formed by diblock copolymers will allow the development of ordered structures with high optical and magnetic contrast between the different regions. In this paper we investigate the effect of homopolymer and diblock copolymer properties on the cluster size. We find that in homopolymer solutions, the cluster size reaches a minimum at a specific chain molecular weight (MW). In the case of diblock copolymers, the cluster size is set by the MW of the block with the stronger affinity to the metal surface.

Effect of Temperature on the Kinetics of Nanocluster Nucleation and Growth in Polymeric Media

AbstractThe synthesis of metal nanoclusters in a polymeric environment has been shown to yield nearly monodisperse particles, whose size is controlled by the strength of the polymer/metal interactions. Although the phenomenon is quite general, little is known regarding the mechanism by which the polymer controls nanocluster size. Previous studies of the kinetics of nanocluster growth in polymeric melts above the glass transition temperature (Tg) showed that the nanoparticle size is set by the critical cluster size rather than the rate of metal precursor transport. In this paper we examined the kinetics of iron-oxide (Fe2O3) nanocluster formation in two polymer melts below their Tg: polystyrene (PS) and poly(methyl methacrylate) (PMMA). We found that the rate of particle formation is nucleation-controlled for both PS and PMMA, similarly to the same process above Tg, while the growth stage is diffusion limited. Transmission electron microscopy (TEM) revealed needlelike particles morphology with larger average dimensions as the temperature is elevated towards polymer matrix Tg. The stabilizing effect of the polymer chains on the growth of the nanoparticles was dominant when the synthesis was performed in solution or in the melt, allowing the polymer to adsorb on the cluster. However, below its Tg the chains were not free to move and conform to the nanocluster surface, and hence, capping occurred when the cluster growth limitation was imposed by the geometric confines set by the voids in the polymer matrix.

Synthesis of metal nanoclusters within microphase-separated diblock copolymers: sodium carboxylate vs carboxylic acid functionalization

Conversion of carboxylic acid groups, within the morphologies of [MTD] 400[NORCOOH] 50 diblock copolymers, to the sodium carboxylate form, [MTD] 400[NORCOONa] 50, results in large increases in both the rate and extent of transition metal and rare earth ion uptake from metal acetates, chlorides, nitrates, and sulfates. A[MTD] 400[NORCOONa] 50 film was subjected to four consecutive Ag + loading and reduction sequences, resulting in a cumulative loading of approximately 26 wt% Ag in the overall polymer/Ag composite. Mean crystal diameters of 37, 50, 64, and 65 Å were estimated following the first, second, third, and fourth, loading and reduction sequences, respectively. During a single loading and reduction sequence, cluster size (ca. 30 Å) within [MTD] 400[NORCOOH] 50 was found to be relatively insensitive to the extent of Ag + uptake, for loadings between 40 and 500 mg Ag +/g polyNORCOOH, consistent with a nucleation-controlled cluster formation process.

Synthesis of metal nanoclusters within microphase-separated diblock copolymers: ICP-AES analysis of metal ion uptake

The rate and extent of aqueous metal ion transport (Ag +, Au +3, Cu +2, Eu +2, Eu +3, Fe +2, Fe +3, Gd +3, Ni +2, Pd +2, Pt +2, and Pt +4) into microphase-separated block copolymers of methyl-tetracyclododecene (MTD) and 2-norbornene-5,6,-dicar☐ylic acid (NORCOOH) was monitored using inductively coupled plasma atomic emission spectroscopy. Continuous interconnected polyNORCOOH domains were found to be necessary for metal ion uptake. The metal-bound car☐ylate ions in the polyNORCOOH domains can be re-protonated by hydrogen reduction, rendering them active for further participation in metal binding. Following reduction, metal nanocluster-containing films were characterized using wide-angle X-ray scattering, infrared spectroscopy, and ultraviolet-visible spectroscopy.

Synthesis of metal nanoclusters within microphase-separated diblock copolymers: a ‘universal’ approach

A general methodology has been established for the synthesis of transition metal nanoclusters within the carboxylic acid functionalized domains of microphase-separated block copolymer films. In this technique the films are soaked in aqueous metal salt solutions prior to reduction of the sequestered metal ions with hydrogen or aqueous NaBH 4. Transmission electron microscopy observation, scanning transmission electron microscopy observation, electron scattering analysis and wide-angle X-ray scattering analysis were used to characterize the size, composition and crystal structure of the resulting metal nanoclusters.