Au Hybrid Research Articles

Dendron-Mediated Engineering of Interparticle Separation and Self-Assembly in Dendronized Gold Nanoparticles Superlattices.

Self-assembly of nanoparticles into designed structures with controlled interparticle separations is of crucial importance for the engineering of new materials with tunable functions and for the subsequent bottom-up fabrication of functional devices. In this study, a series of lipophilic, highly flexible, disulfide dendritic wedges (generations 0-4), based on 2,2-bis(hydroxymethyl)propionic acid, was designed to bind Au nanoparticles with a thiolate bond. By controlling the solvent evaporation rate, the corresponding dendron-capped Au hybrids were found to self-organize into hexagonal close-packed (hcp) superlattices. The interparticular spacing was progressively varied from 2.2 to 6.3 nm with increasing dendritic generation, covering a range that is intermediate between commercial ligands and DNA-based ligand shells. Dual mixtures made from some of these dendronized hybrids (i.e., same inner core size but different dendritic covering) yielded binary superlattice structures of unprecedented single inorganic components, which are isostructural with NaZn13 and CaCu5 crystals.

Laser-induced transformation of supramolecular complexes: approach to controlled formation of hybrid multi-yolk-shell Au-Ag@a-C:H nanostructures.

In the present work an efficient approach of the controlled formation of hybrid Au–Ag–C nanostructures based on laser-induced transformation of organometallic supramolecular cluster compound is suggested. Herein the one-step process of the laser-induced synthesis of hybrid multi-yolk-shell Au-Ag@a-C:H nanoparticles which are bimetallic gold-silver subnanoclusters dispersed in nanospheres of amorphous hydrogenated a-C:H carbon is reported in details. It has been demonstrated that variation of the experimental parameters such as type of the organometallic precursor, solvent, deposition geometry and duration of laser irradiation allows directed control of nanoparticles’ dimension and morphology. The mechanism of Au-Ag@a-C:H nanoparticles formation is suggested: the photo-excitation of the precursor molecule through metal-to-ligand charge transfer followed by rupture of metallophilic bonds, transformation of the cluster core including red-ox intramolecular reaction and aggregation of heterometallic species that results in the hybrid metal/carbon nanoparticles with multi-yolk-shell architecture formation. It has been found that the nanoparticles obtained can be efficiently used for the Surface-Enhanced Raman Spectroscopy label-free detection of human serum albumin in low concentration solution.

Annealing effect: Controlled modification of the structure, composition and plasmon resonance of hybrid Au–Ag/C nanostructures

Here we present a novel approach to the synthesis of hybrid Au–Ag/C nanoparticles (NPs) which were found to be carbon nanospheres containing dispersed Au–Ag bimetallic nanoparticles (1–5nm). The Au–Ag/C NPs were obtained by laser-induced liquid phase deposition from solutions of supramolecular complex. It was revealed that subsequent annealing procedure of Au–Ag/C NPs at various temperatures over the range 100–600°C allows variation and directed control of NPs’ morphology and composition (relative contents of principal components). For nanoscale carbon material the critical evaporation temperature was found to be about 300°C, while for Ag and Au components – 500°C and 600°C accordingly. The morphology and composition variation makes possible tuning of the surface plasmon resonance characteristics that opens an efficient way of the NPs’ functional properties control, like for example Surface-Enhanced Raman Scattering (SERS). It was found that the obtained hybrid Au–Ag/C NPs display pronounced SERS activity with the enhancement factor (EF) ca. 105.

Enhancement of surface enhanced raman scattering from arrays of hybrid Au–Ag nanoparticles via localised surface plasmon resonance

The enhancement of surface enhanced raman scattering of the hybrid Au–Ag triangular nanostructure arrays via localised surface plasmon resonance is systematically investigated. The hybrid nanostructure can prevent the pure silver nanoparticles from oxidation and the stability of Au–Ag nanoparticles compared with non-coated Ag nanoparticles has been verified. Discrete dipole approximation calculated results show the size of the nanoparticle has an important effect on localised surface plasmon resonance of the hybrid nanostructure. Nanosphere lithography is used to fabricate the hybrid nanoparticle arrays with different sizes of nanoparticle. Both theoretical calculations and experimental results show that with an increase in size of the nanoparticle, positions of localised surface plasmon resonance peak are less strongly redshifted and peak of the surface enhanced Raman scattering of the arrays is obviously strengthened. A maximum intensity of the surface enhanced raman scattering can be achieved when the localised surface plasmon resonance wavelength of the hybrid Au–Ag nanoparticle arrays well match the laser excitation wavelength.

Carbon-supported TiO2–Au hybrids as catalysts for the electrogeneration of hydrogen peroxide: Investigating the effect of TiO2 shape

TiO2–Au hybrid materials are promising as electrocatalysts for the in situ production of H2O2 via the oxygen reduction reaction (ORR). However, the synthesis of uniform and well-controlled TiO2–Au materials, which is crucial to establish morphology–performance relationships, remains challenging. We describe herein the synthesis of hybrid materials composed of TiO2 colloidal spheres and wires decorated with Au nanoparticles. We employed TiO2 colloidal spheres and wires as physical templates for Au deposition, which enabled the uniform deposition of Au NPs with monodisperse sizes over the TiO2 surface. Then, the electrocatalytic activities toward the electrogeneration of H2O2 by the ORR were investigated as a function of the TiO2 shape and TiO2–Au loading on Vulcan XC-72R carbon. We found that the electrocatalytic activities were strongly dependent on the TiO2 shape and TiO2–Au loading in the catalysts. The utilization of TiO2 colloidal spheres led to higher activities relative to pure carbon and commercial Pt/C, and the optimal TiO2–Au loading corresponded to 3%. Conversely, the TiO2 wires led to detrimental effects over the catalytic performances for all hybrid materials. These results could be explained based on the morphological and conductivity differences among TiO2–Au/C electrode materials. We believe the results described herein can have important implication for the design of TiO2-based hybrid nanostructures for the electrogeneration of H2O2 by the ORR.

Pulsed field probe of real time magnetization dynamics in magnetic nanoparticle systems

Magnetic nanoparticles (MNPs) are extensively used in biotechnology. These applications rely on magnetic properties that are a keen function of MNP size, distribution, and shape. Various magneto-optical techniques, including Faraday Rotation (FR), Cotton-Mouton Effect, etc., have been employed to characterize magnetic properties of MNPs. Generally, these measurements employ AC or DC fields. In this work, we describe the results from a FR setup that uses pulsed magnetic fields and an analysis technique that makes use of the entire pulse shape to investigate size distribution and shape anisotropy. The setup employs a light source, polarizing components, and a detector that are used to measure the rotation of light from a sample that is subjected to a pulsed magnetic field. This magnetic field “snapshot” is recorded alongside the intensity pulse of the sample's response. This side by side comparison yields useful information about the real time magnetization dynamics of the system being probed. The setup is highly flexible with variable control of pulse length and peak magnitude. Examining the raw data for the response of bare Fe3O4 and hybrid Au and Fe3O4 nanorods reveals interesting information about Brownian relaxation and the hydrodynamic size of these nanorods. This analysis exploits the self-referencing nature of this measurement to highlight the impact of an applied field on creating a field induced transparency for a longitudinal measurement. Possible sources for this behavior include shape anisotropy and field assisted aggregate formation.

Hybrid Au–SiO2Core–Satellite Colloids as Switchable SERS Tags

Gold–silica self-assembled nanostructures are reported as multiplex surface enhanced Raman scattering (SERS) tags for bioimaging applications. These hybrid colloidal particles were obtained by heteroassembly of Au–SiO2 Janus particles with smaller Au spheres and two Raman-active molecules that can be independently imaged by varying the wavelength of the excitation laser. The Janus structure of Au–SiO2 not only directs the assembly but also provides physical separation of the Raman tags and colloidal stability thereby facilitating complete silica encapsulation. The bioimaging capabilities of this system are demonstrated through SERS mapping of individual cells.

Synthesis of magnetic Fe3O4–Au hybrids for sensitive SERS detection of cancer cells at low abundance

This work reports a facile synthesis of magnetic hybrids (Fe3O4-Au hybrids) with high SERS activity for detecting a low abundance of cancer cells. We labeled Raman reporter molecule 4-aminothiophenol (4-ATP) and the antibody of CEA (anti-CEA) on Fe3O4-Au hybrid nanoparticles (anti-CEA/4-ATP/Fe3O4-Au) as SERS tags and anti-CEA-labeled Au NPs (anti-CEA/Au) as SERS-active substrates to improve detection sensitivity. In the presence of CEA positive-expressed cancer cells (such as non-small lung cancer cells, A549), sandwich structures were formed as both SERS tags and SERS-active substrates could be bound to CEA at cell surfaces, leading to the formation of SERS hot spots at the junction of SERS tags and SERS-active substrates. As a result, an enhanced SERS signal of 4-ATP arose, which could be used to detect CEA on cell surfaces. This assay can specifically detect CEA-expressed A549 cells at a very low abundance (∼10 cells mL-1) and can be used for evaluating CEA expression levels of different cancer cells line. This assay has the advantages of high sensitivity (because the SERS technique itself enables the detection of very low concentration analytes, even single molecules), high specificity (because of the enhanced SERS signal arising in sandwich configuration, which is formed in specific antigen-antibody interaction events), and high efficiency (because the magnetic SERS tags can concentrate the captured cells and separate them from the complex detection system without repetitive washing steps). These features make our developed assay a rapid and facile method to sensitively detect a low abundance of cancer cells.

Preparation of zinc oxide nanoparticle–reduced graphene oxide–gold nanoparticle hybrids for detection of NO2

A novel NO2 gas sensor bas been fabricated using ZnO–rGO–Au hybrids as sensing materials, which exhibit excellent sensing performances operated at 80 °C.

Fabrication of core–multishell MWCNT/Fe3O4/PANI/Au hybrid nanotubes with high-performance electromagnetic absorption

MWCNT/Fe3O4/PANI/Au hybrids achieve high-performance electromagnetic absorption as gold induces more EM waves to be transmitted into the hybrids, thus generating significant interfacial polarization.

Tuning plasmonic and chemical enhancement for SERS detection on graphene-based Au hybrids.

Various graphene-based Au nanocomposites have been developed as surface-enhanced Raman scattering (SERS) substrates recently. However, efficient use of SERS has been impeded by the difficulty of tuning SERS enhancement effects induced from chemical and plasmonic enhancement by different preparation methods of graphene. Herein, we developed graphene-based Au hybrids through physical sputtering gold NPs on monolayer graphene prepared by chemical vapor deposition (CVD) as a CVD-G/Au hybrid, as well as graphene oxide-gold (GO/Au) and reduced-graphene oxide (rGO/Au) hybrids prepared using the chemical in situ crystallization growth method. Plasmonic and chemical enhancements were tuned effectively by simple methods in these as-prepared graphene-based Au systems. SERS performances of CVD-G/Au, rGO/Au and GO/Au showed a gradually monotonic increasing tendency of enhancement factors (EFs) for adsorbed Rhodamine 6G (R6G) molecules, which show clear dependence on chemical bonds between graphene and Au, indicating that the chemical enhancement can be steadily controlled by chemical groups in a graphene-based Au hybrid system. Most notably, we demonstrate that the optimized GO/Au was able to detect biomolecules of adenine, which displayed high sensitivity with a detection limit of 10(-7) M as well as good reproducibility and uniformity.

Effect of defects and film thickness on the optical properties of ZnO–Au hybrid films

Thickness and defects effects on the optical properties of ZnO–Au hybrid films were studied using optical and electronic structural studies.

Magnetic anisotropy of Au/Co/Au/MgO heterostructure: Role of the gold at the Co/MgO interface

The influence of Au interlayer on the out-of-plane magnetic anisotropy of Au/Co/Au/MgO/Au heterostructures with ultra-thin Co wedge-shaped film was investigated by means of ferromagnetic resonance. It was found that introduction of a single Au monolayer enhances the surface anisotropy of the Co/MgO interface. An occurrence of a large perpendicular anisotropy with respect to the Co overlayer suggests that the largest contribution to the interface anisotropy energy originates from the Au/Co interface as a result of strong Au and Co orbitals hybridization.

Reduced graphite oxide/SnO2/Au hybrid nanomaterials for NO2sensing performance at relatively low operating temperature

The reduced graphene oxide/SnO2/Au (rGO/SnO2/Au) hybrid nanomaterials have been prepared by a one-step hydrothermal process with a property of gas sensing at a relatively low operating temperature. The structure and morphology characteristics of the resultant product were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM). The sizes of the Au nanoparticles of rGO/SnO2/Au-1 to rGO/SnO2/Au-4 range from about 12 to 90 nm, respectively. To demonstrate the usage of such hybrid nanomaterials, chemical gas sensors have been fabricated and investigated for NO2 detection. It is found that the rGO/SnO2/Au sensor exhibits much better response/recovery time which is 19/20 s at the optimal operating temperature of 50 °C to 5 ppm NO2, compared with the pure rGO (798/8319 s) and rGO/SnO2 (427/908 s). The enhanced sensing features can be attributed to the heterojunctions with the highly conductive graphene, SnO2 thin film and Au nanoparticles.

Restructural confirmation and photocatalytic applications of graphene oxide–gold composites synthesized by Langmuir–Blodgett method

We present a first report on the use of Langmuir Blodgett (LB) technique for the synthesis of edge decorated graphene oxide gold (GO–Au) nanostructures by simple manipulation of electrostatic interactions. The GO–Au nanostructures when characterized using spectroscopy, surface, chemical and micro structural techniques, displayed unique physical and structural properties. The results re-established the theoretical corroboration that the carboxyl groups are primarily located at the edges of the 2D sheets of GO. The exploitation of air–water interface platform makes this process novel and fundamentally different from existing protocols for synthesis of GO–metal composites. These GO–Au hybrid materials favoured visible-light driven plasmonic photo catalysis together with enhanced charge separation and transportation properties, resulting in the augmentation of photocatalytic activity and conductivity with high transmittance. A plausible reaction mechanism for the degradation of pollutant dye and the role of gold nanoparticles (NPs) on GO has been established.

Facile synthesis of the SiO2/Au hybrid microspheres for excellent catalytic performance

Abstract

Enhancement of Pd-catalyzed Suzuki–Miyaura coupling reaction assisted by localized surface plasmon resonance of Au nanorods

Localized surface plasmon resonance (LSPR) induced by Au nanorods was employed to enhance the catalytic activity of Pd-driven Suzuki–Miyaura coupling reaction under light irradiation at ambient temperatures. The optical properties of the obtained Pd–Au/SiO2 samples were investigated by UV–vis spectroscopy, which exhibit intense absorption bands in the low energy region, and the ratio between Pd NPs and Au nanorods has a significant impact on turning the optical property and catalytic performance of Pd–Au alloy. The optimized weight ratio of Pd–Au hybrid catalyst for Suzuki–Miyaura coupling reaction under light irradiation was found to be 1:0.5. The enhanced activity can be attributed to the cooperative promoting effects between Au nanorods and Pd nanoparticles in effective conversion of solar energy for generation of energetic electrons to activate the palladium and increasing temperature in the reaction solution.

Transmission electron microscopy of unstained hybrid Au nanoparticles capped with PPAA (plasma-poly-allylamine): Structure and electron irradiation effects

Hybrid (organic shell–inorganic core) nanoparticles have important applications in nanomedicine. Although the inorganic components of hybrid nanoparticles can be characterized readily using conventional transmission electron microscopy (TEM) techniques, the structural and chemical arrangement of the organic molecular components remains largely unknown. Here, we apply TEM to the physico-chemical characterization of Au nanoparticles that are coated with plasma-polymerized-allylamine, an organic compound with the formula C3H5NH2. We discuss the use of energy-filtered TEM in the low-energy-loss range as a contrast enhancement mechanism for imaging the organic shells of such particles. We also study electron-beam-induced crystallization and amorphization of the shells and the formation of graphitic-like layers that contain both C and N. The resistance of the samples to irradiation by high-energy electrons, which is relevant for optical tuning and for understanding the degree to which such hybrid nanostructures are stable in the presence of biomedical radiation, is also discussed.

Defect Enhanced Efficient Physical Functionalization of Graphene with Gold Nanoparticles Probed by Resonance Raman Spectroscopy

We demonstrate efficient physical functionalization of single layer graphene with Au nanoparticles mediated by in-plane defects in graphene grown by a chemical vapor deposition technique. The effect of an ultrathin Au layer on the single layer, bi layer, and few layer graphene with intrinsic defects was studied by resonance Raman spectroscopy and high resolution transmission electron microscopy (HRTEM). We observed a striking enhancement in the intensity of sharp D and D′ bands after sputter deposition of an ultrathin Au layer on graphene. In contrast, G and 2D bands show a lower enhancement in intensity and a change in line width due to the charge transfer from Au to the graphene and strong interaction between the Au and graphene layers, respectively. X-ray photoelectron spectroscopy (XPS) analysis shows a 40% decrease in integrated intensity ratio of sp3 and sp2 bands in C-1s spectra after Au functionalization indicating bonding of Au atoms preferentially at the defect sites in graphene. This was further substantiated by HRTEM imaging and position dependent Raman spectral line shape analysis. The calculations of interdefect distance and areal defect density from the Raman analysis on the graphene–Au hybrid are in close agreement with the HRTEM analysis. Further, Raman spectral line shape dependence of Au functionalization on the number of layers in graphene reveals that Au functionalized single layer graphene behaves like a pristine bi layer graphene due to strong interaction between Au and the graphene layer. These results open up possibilities for efficient physical functionalization of graphene with foreign atoms through defect engineering for novel applications of graphene in catalysis, biosensors, and optoelectronic and photonic devices.

Thermo-, pH-, and light-responsive poly(N-isopropylacrylamide-co-methacrylic acid)--Au hybrid microgels prepared by the in situ reduction method based on Au-thiol chemistry.

In recent years, it has been an attractive challenge to fabricate multiple stimuli-responsive hybrid microgels composed of polymer microgel and gold nanoparticle (AuNP). Herein, we report on the detailed synthesis of poly(N-isopropylacrylamide-co-methacrylic acid)--Au hybrid microgels by in situ reduction of gold precursor in the presence of thiol-functionalized poly(N-isopropylacrylamide-co-methacrylic acid) microgels. The as-synthesized hybrid microgels showed well-defined swelling/deswelling transition in response to the surrounding temperature, pH, and light irradiation. The hybrid microgels had a unique microstructure where a large number of AuNP's distribute mainly in the interior of microgel with a fluff-like surface. The plasmonic property of the hybrid microgels can be modulated through the volume phase transition induced by the external triggers such as temperature and pH. In the reduction of 4-nitrophenol catalyzed by the hybrid microgels, it was found that the reaction rate did not increase monotonously with temperature but greatly decreased in a certain temperature range, showing a tunable catalytic activity.