Synthesis and characterization of gold at gold(i)-thiomalate core at shell nanoparticles

Highly branched and ultrathin Au nanodendrites for reduction catalysis

Two-dimensional (2D) materials have garnered significant attention due to their distinctive physicochemical properties, with 2D noble metal nanodendrites being particularly intriguing in terms of their properties and functional prospects. However, the synthesis of ultrathin and highly branched gold nanodendrites (AuNDs) still poses challenges. In this study, we successfully achieved the synthesis of highly branched 2D AuNDs with a thickness of 4 nm by employing a carboxyl-functionalized C22-tailed surfactant along with the co-directing agent 2-mercaptonicotinic acid (2-MNA). The careful selection of specific thiol molecules such as 2-MNA is crucial for controlling the degree of branching and promoting the formation of ultrathin nanodendrites. Furthermore, we extended this method to synthesize alloy nanodendrites (AuAg NDs and AuCoAg NDs) using a similar approach. Due to their highly branched and ultrathin two-dimensional morphology, these prepared AuNDs exhibit excellent catalytic performance in the model reaction for 4-NP reduction. This thiol-induced synthesis strategy for AuNDs opens up new possibilities for designing other Au nanomaterials with an ultrathin morphology/structure.

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.

Room-Temperature Harvesting Oxidase-Mimicking Enzymes with Exogenous ROS Generation in One Step

Despite the advantages of low cost, high stability, and activities, a majority of nanozymes rely on strict synthesis conditions and precise size/structure control, hindering the stable, bulk, and high-yield production that is necessary for general use. To facilitate the transition of nanozymes from benchtop to real-world applications, we herein present a one-step approach, which only needs mixing of two broad commercialized reagents at room temperature, to harvest gold nanoparticles-bovine serum albumin (BSA) nanocomposite (BSA-Au) with distinct oxidase-like activity and good stability in a broad range of harsh conditions. Density functional theory (DFT) calculations demonstrate the oxidase-like activity of BSA-Au stemming from thermodynamically and kinetically favored facets for O2 activation. The reactive oxygen species (ROS) generation of BSA-Au contributes to the catalytic activities and further enables water sterilization and antibacterial applications against superbugs. This one-step strategy promises great potential in bulk production of nanozyme for broad application beyond laboratory use.

Impact of a Gold Nanocolloid Electrolyte on Li2O2 Morphology and Performance of a Lithium-Oxygen Battery

Aprotic lithium-oxygen batteries currently suffer from poor cyclic stability and low achievable energy density. Herein, gold nanoparticles capped with mercaptosuccinic acid are dispersed in 1.0 M LiClO₄/dimethyl sulfoxide (DMSO) as a novel electrolyte for lithium-oxygen batteries. Morphological and electrochemical analyses indicate that film-like amorphous lithium peroxide is formed using the gold nanocolloid electrolyte instead of bulk crystals in battery discharging, which apparently increases the conductivity and accelerates the decomposition kinetics of discharge products in recharging, accompanied by the release of incorporated gold nanoparticles with the decomposition of lithium peroxide into the electrolyte. Experiments and theoretical calculations further demonstrate that the suspended gold nanoparticles in the electrolyte can adsorb some intermediates generated by an oxygen reduction reaction, which effectively alleviates the cleavage of the electrolyte and impedes the corrosion of the lithium anode. As a result, the life span of lithium-oxygen batteries is dramatically increased from 55 to 438 cycles, and the rate performance and full-discharge capacity are also massively enhanced. The battery failure is attributed to the degradation of gold nanocolloid electrolytes, and further studies on improvement of colloid stability during battery cycling are underway.

Surfactant Design Strategy for One-Pot Seedless Synthesis of Hollow Mesoporous AuAg Alloy Nanospheres

Hollow gold (Au)-based nanostructures have recently been developed for various applications. However, current nanosynthesis approaches have not yet successfully been implemented for precisely engineering hollow Au-based nanostructures with uniform and well-defined mesoporous shell frameworks. Here, we develop an easy one-pot seedless strategy for fabricating hollow mesoporous AuAg (h-mesoAuAg) nanospheres by combining the galvanic replacement reaction with the surfactant-templated growth. Thiol-terminated multifunctional C₂₂H₄₅N⁺(CH₃)₂-C₃H₆-SH (Cl^-) (C₂₂N-SH) as the functional surfactant is the key that facilitates the formation of covalently stable C₂₂N-S-Au(I) and C₂₂N-S-Ag(I) intermediates. Such intermediates template in situ growth of mesoAuAg shell on initially nucleated Ag-rich seeds through the galvanic replacement reaction. Hierarchically hollow/mesoporous nanostructures and corresponding optical responses of h-mesoAuAg are also precisely engineered by tailoring synthetic parameters. With structural and compositional advantages, h-mesoAuAg nanospheres exhibit promising electrochemical performances toward methanol oxidation reaction and nonenzymatic glucose sensor.

Mesoporous gold nanospheres via thiolate-Au(i) intermediates

This manuscript reports a facile yet effective surfactant-templated synthesis methodology to grow in situ metallic gold mesoporous nanospheres for methanol electrooxidation.

Mesoporous gold (mesoAu) nanospheres support enhanced (electro)catalytic performance owing to their three-dimensional (3D) interior mesochannels that expose abundant active sites and facilitate electron/mass transfers. Although various porous Nanostructured Au has been fabricated by electrochemical reduction, alloying–dealloying and hard/soft templating methods, successful synthesis of mesoAu nanospheres with tailorable sizes and porosities remains a big challenge. Here we describe a novel surfactant-directed synthetic route to fabricate mesoAu nanospheres with 3D interconnected mesochannels by using the amphiphilic surfactant of C₂₂H₄₅N⁺(CH₃)₂–C₃H₆–SH (Cl^–) (C₂₂N–SH) as the mesopore directing agent. C₂₂N–SH can not only self-reduce trivalent Au(iii)Cl₄^– to monovalent Au(i), but also form polymeric C₂₂N–S–Au(i) intermediates via covalent bonds. These C₂₂N–S–Au(i) intermediates facilitate the self-assembly into spherical micelles and inhibit the mobility of Au precursors, enabling the crystallization nucleation and growth of the mesoAu nanospheres via in situ chemical reduction. The synthetic strategy can be further extended to tailor the sizes/porosities and surface optical properties of the mesoAu nanospheres. The mesoAu nanospheres exhibit remarkably enhanced mass/specific activity and improved stability in methanol electrooxidation, demonstrating far better performance than non-porous Au nanoparticles and previously reported Au nanocatalysts. The synthetic route differs markedly from other long-established soft-templating approaches, providing a new avenue to grow metal nanocrystals with desirable nanostructures and functions.

A repertoire of biomedical applications of noble metal nanoparticles

The emerging properties of noble metal nanoparticles are attracting huge interest from the translational scientific community. In this feature article, we highlight recent advances in the adaptation of noble metal nanomaterials and their biomedical applications in therapeutics, diagnostics and sensing.

Electron Dose-Controlled Formation, Growth, and Assembly of Nanoclusters and Nanoparticles from Aurophilic Au(I)-Thiolate Ensemble on Surfaces

The ability to precisely control electron irradiation-induced formation, growth, and assembly of nanoclusters or nanoparticles on a solid surface is important for design and creation of catalytically or chemically active surface sites and interfaces free from chemical reducing agents. Here, we show the results of an investigation of the electron dose-controlled formation, growth, and assembly of nanoclusters and nanoparticles in a molecularly assembled thin film of Au(I)-thiolate motifs on a substrate, highlighting an in situ monitoring of the evolution of morphology under controlled electron dose. With aurophilic motifs of Au(I)-thiolate being confined by electrostatic interactions, the sizes of Au nanoclusters and nanoparticles were shown to increase with electron dose, revealing a propensity of a string alignment of the grown nanoclusters and nanoparticles. This growth preference to one-dimensional assembly is supported by the analysis of the surface reaction kinetics in terms of the surface density of electron dose for the growth of the nanoclusters and nanoparticles. The electron dose-controlled size-focusing and directional assembly of nanoclusters and nanoparticles may be exploited as new strategy for the precise control of nanoclusters or nanoparticles and their assemblies on solid surfaces not only free from chemical reducing agent but also with the ability of visual monitoring of the morphological evolution during growth.

Indole Derivative-Capped Gold Nanoparticles as an Effective Bactericide in Vivo

We synthesize indole derivative-capped gold nanoparticles (Au_IDs) via a straightforward route to fight multidrug-resistant (MDR) bacteria. When gold nanoparticles are modified with two indole derivatives, tryptophan and 5-aminoindole, they exhibit excellent antibacterial activities against both laboratory antibiotic-sensitive and MDR bacteria. Au_IDs possess remarkable bactericidal activities against MDR bacteria killing 99.9% of MDR Escherichia coli and polymyxin-resistant Klebsiella pneumoniae after 0.5 h of incubation, which are superior to clinical antibiotics including polymyxin B and cefotaxime. By evaluating the potential of Au_IDs in wound cure, Au_IDs show outstanding capability in MDR bacterial wound infection. Our findings provide new candidates for the development of bactericides and the fabrication of wound dressings for treating MDR infection.

Stabilization of Ag-Au Bimetallic Nanocrystals in Aquatic Environments Mediated by Dissolved Organic Matter: A Mechanistic Perspective

Gold and silver nanoparticles can be stabilized endogenously within aquatic environments from dissolved ionic species as a result of mineralization induced by dissolved organic matter. However, the ability of fulvic and humic acids to stabilize bimetallic nanoparticles is entirely unexplored. Elucidating the formation of such particles is imperative given their potential ecological toxicity. Herein, we demonstrate the nucleation, growth, and stabilization of bimetallic Ag-Au nanocrystals from the interactions of Ag⁺ and Au³⁺ with Suwannee River fulvic and humic acids. The mechanisms underpinning the stabilization of Ag-Au alloy NPs at different pH (6.0-9.0) values are studied by UV-vis spectrophotometry, X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED). Complexation of free Ag⁺ and Au³⁺ ions with the Lewis basic groups (carbonyls, carboxyls, and thiols) of FA and HA, followed by electron-transfer from redox-active moieties present in dissolved organic matter initiates the nucleation of the NPs. Alloy formation and interdiffusion of Au and Ag atoms are further facilitated by a galvanic replacement reaction between AuCl₄^- and Ag. Charge-transfer from Au to Ag stabilizes the formed bimetallic NPs. A more pronounced agglomeration of the Ag-Au NPs is observed when HA is used compared to FA as the reducing agent. The bimetallic NPs are stable for greater than four months, which suggests the possible persistence and dispersion of these materials in aquatic environments. The mechanistic ideas have broad generalizability to reductive mineralization processes mediated by dissolved organic matter.

Nanoscale Lacing by Electrons

The ability to harness the optical or electrical properties of nanoscale particles depends on their assembly in terms of size and spatial characteristics which remains challenging due to lack of size focusing. Electrons provide a clean and focusing agent to initiate the assembly of nanoclusters or nanoparticles. Here an intriguing route is demonstrated to lace gold nanoclusters and nanoparticles in string assembly through electron-initiated nucleation and aggregative growth of Au(I)-thiolate motifs on a thin film substrate. This size-focused assembly is demonstrated by controlling the electron dose under transmission electron microscopic imaging conditions. The Au(I)-thiolate motifs, in combination with the molecularly mediated alignment, facilitate the interstring electrostatic and intrastring aurophilic interactions, which functions as a molecular template to aid electron-initiated 1D lacing. The findings demonstrate a hierarchical route for the 1D assemblies with size and spatial tunable catalytic, optical, sensing, and diagnostic properties.

Recent advances in nanomedicines for the treatment of rheumatoid arthritis

Schematic illustration of inflammatory microenvironment in inflamed joints and events occurring in rheumatoid arthritis.

Synthesis of gold Nanoshells through Improved Seed-Mediated Growth Approach: Brust-like, in Situ Seed Formation

Gold nanoshells have shown great potentials in various fields. However, the widely used seed-mediated growth method based on a silica template for gold nanoshells is a complex and time-consuming procedure. In this work, mercaptosilica was first used as a template to synthesize gold nanoshells through improved seed-mediated growth method. It is verified that gold seeds were formed and attached onto the mercaptosilica nanospheres through Brust-like, in situ process, which makes this method extremely time-saving and easy to manipulate. Importantly, the key factors affecting the in situ process were demonstrated, allowing fine control on the synthesis in a highly reproducible manner. The as-synthesized nanoshells are monodisperse with well-defined morphology and tunable near-IR plasmon resonance. Furthermore, other metal nanoparticles such as Pt and Pd could be grafted onto the surface of mercaptosilica nanospheres through the same Brust-like, in situ process. These provide new insights into seed attachment, and the improved seed-mediated growth approach based on Brust-like, in situ seed formation will take an important step forward toward the widespread application of gold nanoshells.

Bimetallic Au@Pt@Au core-shell nanoparticles on graphene oxide nanosheets for high-performance H2O2 bi-directional sensing

Bimetallic Au@Pt@Au triple-layered core-shell nanoparticles consisting of a Au core, Pt inner shell, and an outer shell composed of Au protuberances on graphene oxide (GO) nanosheets were successfully prepared by a galvanic replacement and reagent reduction reaction. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and cyclic voltammetry (CV) were employed to characterize the GO-supported Au@Pt@Au (GO/Au@Pt@Au) nanocomposites. The as-prepared catalyst has peroxidase-like activity, allowing it to express high electrocatalytic ability in hydrogen peroxide (H₂O₂) oxidation and reduction, thus leading to a highly sensitive H₂O₂ bi-directional amperometric sensing. The bi-directional sensor showed a linear range from 0.05 μM to 17.5 mM with a detection limit of 0.02 μM (S/N = 3) at an applied potential of +0.5 V and a linear range from 0.5 μM to 110 mM with a detection limit of 0.25 μM (S/N = 3) at an applied potential of -0.3 V. The proposed sensor was tested to determine H₂O₂ released from living cells and shows good application potential in biological electrochemistry.

Synthesis of ultra-small cysteine-capped gold nanoparticles by pH switching of the Au(I)-cysteine polymer

We report a synthetic approach for the production of ultra-small (0.6 nm) gold nanoparticles soluble in water with a precise control of the nanoparticle size. Our synthetic approach utilizes a pH-depending Au-cysteine polymer as a quencher for the AuNPs grown. The method extends the synthetic capabilities of nanoparticles with sizes down to 1 nm. In addition to the strict pH control, the existence of free -SH groups present in the mixture of reaction has been observed as a key requirement for the synthesis of small nanoparticles in mild conditions. UV-Vis, SAXS, XANES, EXAFS and HR-TEM, has been used to determinate the particle size, characterization of the gold precursor and gold-cysteine interaction.

Surface chemistry of thiomalic acid adsorption on planar gold and gold nanoparticles

The self-assembly of thiomalic acid (TMA) on Au(111) and on preformed Au nanoparticles (AuNPs) protected by weak ligands has been studied by X-ray photoelectron spectroscopy (XPS) and electrochemical techniques. Results show that TMA is adsorbed on the Au(111) surface as thiolate species with a small amount of atomic sulfur (∼10%) and a surface coverage lower than that found for alkanethiols due to steric factors. The amount of atomic sulfur markedly increases when the TMA is adsorbed on AuNPs by the ligand exchange method. We propose that the atomic sulfur is produced as a consequence of C-S bond cleavage, a process that is more favorable at defective sites of the AuNPs surface. The bond scission is also assisted by the presence of the electron-withdrawing carboxy moiety in the α-position relative to the C-S bond. Moreover, the high local concentration of positively charged species increases the stability of the negatively charged leaving group, leading to a higher amount of coadsorbed atomic sulfur. Our results demonstrate that the terminal functionalities of thiols are conditioning factors in the final structure and composition of the adlayers.

On the chiroptical properties of Au(i)–thiolate glycoconjugate precursors and their influence on sugar-protected gold nanoparticles (glyconanoparticles)

The structure of d/l sugar thiolate conjugates used in the preparation of Au(i)–thiolate polymers determines their chiroptical properties.

Self-assembled monolayers of thiolates on metals: a review article on sulfur-metal chemistry and surface structures

A review article on fundamental aspects of thiolate self-assembled monolayers (SAMs) on the (111) and (100) surfaces of the Cu and Ni groups is presented.

Facile preparation of high-quantum-yield gold nanoclusters: application to probing mercuric ions and biothiols

This paper describes an eco-friendly, one-pot strategy for the synthesis of water-soluble, high-quantum-yield gold nanoclusters (AuNCs) stabilized with 11-mercaptoundecanoic acid (MUA) on their surfaces. The as-prepared ultrasmall MUA-AuNCs (1.9 nm) exhibited a quantum yield (QY) of 13%, higher than those of most previously described thiol-protected AuNCs. We applied these MUA-AuNCs as a versatile probe to develop a fluorescence "turn-off" assay for sensing Hg(2+) ions as well as a fluorescence "turn-on" assay for sensing biothiols. The former assay operated through aggregation-induced fluorescence quenching upon interaction of the MUA-AuNCs with Hg(2+) ions in a buffer containing 2,6-pyridinedicarboxylic acid (PDCA); this probe provided high sensitivity and remarkable selectivity over other selected metal ions with a limit of detection (LOD) for Hg(2+) ions of 450 pM and linearity from 2 to 50 nM. In the latter assay for biothiols [i.e., cysteine (Cys), homocysteine (Hcy), glutathione (GSH)], the fluorescence of the Hg(2+)-MUA-AuNCs complexes was turned on because the affinity of Hg(2+) ions toward the SH group of the biothiols was greater than that toward the COOH groups of the MUA units on the surface of the AuNCs. This assay provided good linearity for the tested biothiols, ranging from 10 to 100 nM for Cys, from 10 to 100 nM for Hcy, and from 5 to 75 nM for GSH, with LODs of 5.4, 4.2, and 2.1 nM, respectively. In addition, these environmentally and biologically friendly AuNC probes tested satisfactorily against interference from a range of amino acids.

Disassembly mediated fluorescence recovery of gold nanodots for selective sulfide sensing

We report a one-pot, two-step strategy to synthesize fluorescent gold nanodots (AuNDs) co-modified with 1-(10-mercaptodecyl)-5-methylpyrimidine-2,4-dione (TSH) and 11-mercaptoundecanoic acid (MUA) through a ligand exchange reaction and demonstrate their capability of selective sulfide sensing in aqueous media on the basis of fluorescence recovery.

New findings for the composition and structure of Ni nanoparticles protected with organomercaptan molecules

Here we explore the synthesis of alkanethiol-coated Ni NPs following the one-phase reaction method by Brust et al. The reduction of NiCl2 with NaBH4 in the presence of dodecanethiol (C12SH) yields a complex product that is difficult to identify as illustrated in the figure of merit. We synthesized Ni(II) dodecanethiolate (C12S) (without the addition of NaBH4) for comparison and performed an exhaustive characterization with TEM, HR-TEM, AFM, MFM, XPS, XRD, UV-vis, magnetism, and FT-IR. It is found that the organic coating is not quite a well-organized self-assembled monolayer (SAM) surrounding the Ni cluster as previously reported. XPS and XRD data show slight differences between both syntheses; however, Ni(II) thiolate appears to be more stable than reduced Ni when exposed to ambient air, indicating the propensity of metallic Ni to oxidize. It has been shown that irradiating with TEM electrons over various metal thiolates leads to nanoparticle formation. We irradiated over Ni(II) thiolate and observed no evidence of NP formation whereas irradiating a reduced Ni sample exhibited an ~3.0 nm nanoparticle diameter. Magnetism studies showed a difference between both samples, indicating ferromagnetic character for the reduced Ni sample. According to our results, the product of the synthesis is comprised of ultrasmall metallic clusters embedded in some form of Ni(II) C12S. In this work, we open a discussion of the chemical nature of the core and the shell in the synthesis of Ni NPs protected with organomercaptan molecules.

The chemistry of the sulfur-gold interface: in search of a unified model

Over the last three decades, self-assembled molecular films on solid surfaces have attracted widespread interest as an intellectual and technological challenge to chemists, physicists, materials scientists, and biologists. A variety of technological applications of nanotechnology rely on the possibility of controlling topological, chemical, and functional features at the molecular level. Self-assembled monolayers (SAMs) composed of chemisorbed species represent fundamental building blocks for creating complex structures by a bottom-up approach. These materials take advantage of the flexibility of organic and supramolecular chemistry to generate synthetic surfaces with well-defined chemical and physical properties. These films already serve as structural or functional parts of sensors, biosensors, drug-delivery systems, molecular electronic devices, protecting capping for nanostructures, and coatings for corrosion protection and tribological applications. Thiol SAMs on gold are the most popular molecular films because the resulting oxide-free, clean, flat surfaces can be easily modified both in the gas phase and in liquid media under ambient conditions. In particular, researchers have extensively studied SAMs on Au(111) because they serve as model systems to understand the basic aspects of the self-assembly of organic molecules on well-defined metal surfaces. Also, great interest has arisen in the surface structure of thiol-capped gold nanoparticles (AuNPs) because of simple synthesis methods that produce highly monodisperse particles with controllable size and a high surface/volume ratio. These features make AuNPs very attractive for technological applications in fields ranging from medicine to heterogeneous catalysis. In many applications, the structure and chemistry of the sulfur-gold interface become crucial since they control the system properties. Therefore, many researchers have focused on understanding of the nature of this interface on both planar and nanoparticle thiol-covered surfaces. However, despite the considerable theoretical and experimental efforts made using various sophisticated techniques, the structure and chemical composition of the sulfur-gold interface at the atomic level remains elusive. In particular, the search for a unified model of the chemistry of the S-Au interface illustrates the difficulty of determining the surface chemistry at the nanoscale. This Account provides a state-of-the-art analysis of this problem and raises some questions that deserve further investigation.

Chemiresistive sensing with chemically modified metal and alloy nanoparticles

This review describes the use of chemically modified pure and alloyed metal nanoparticles for chemiresistive sensing applications. Chemically modified metal nanoparticles consist of a pure or alloyed metallic core with some type of chemical coating. Researchers have studied the electronic properties of 1D, 2D, and 3D assemblies of chemically modified metal nanoparticles, and even single individual nanoparticles. The interaction with the analyte alters the conductivity of the sensitive material, providing a signal to measure the analyte concentration. This review focuses on chemiresistive sensing of a wide variety of gas- and liquid-phase analytes with metal nanoparticles coated with organothiols, ions, polymers, surfactants, and biomolecules. Different strategies used to incorporate chemically modified nanoparticles into chemiresistive sensing devices are reviewed, focusing on the different types of metal and alloy compositions, coatings, methods of assembly, and analytes (vapors, gases, liquids, biological materials), along with other important factors.