Au Hybrid Research Articles

Fabrication of fluorescent silica–Au hybrid nanostructures for targeted imaging of tumor cells

Uniform "core-satellite" structured nanoparticles containing organic dye incorporated in the silica shell and fluorescence quenching Au nanoparticles have been synthesized with excellent fluorescent properties, and their targeted imaging application in tumor cells has been investigated.

Hybrid Nanorings: Magnetic Alloy Nanorings Loaded with Gold Nanoparticles: Synthesis and Applications as Multimodal Imaging Contrast Agents (Adv. Funct. Mater. 21/2010)

AbstractMulticomponent Ni7Co3 alloy–Au nanorings can be facilely synthesized at room temperature using metallic Ni7Co3 alloy nanorings as both reducing agent and sacrificial template in water. These novel alloy–Au hybrid nanorings are well biocompatible due to coating with poly(vinylpyrrolidone) and gold nanoparticles. When increasing the molar ratio of alloy to gold salt from 1:1 to 5:1, the number of the gold nanoparticles loaded on the surface of alloy nanorings were found to be decreased, and their morphology was transformed from rod to particle, remaining the ring‐like assemblies. Their saturation magnetization increased due to the ring‐like assemblies, resulting in the enhancement of the signal intensity in Spin–spin relaxation time (T2) weighted magnetic resonance imaging measurement. These alloy–Au hybrid nanocomposites can perform as multimodal imaging contrast agents for cancer cell diagnosis by two‐photon fluorescent imaging and T2‐weighted magnetic resonance imaging. In addition, their potential application for photothermal therapy was preliminarily investigated.

Magnetic Alloy Nanorings Loaded with Gold Nanoparticles: Synthesis and Applications as Multimodal Imaging Contrast Agents

AbstractMulticomponent Ni7Co3 alloy–Au nanorings can be facilely synthesized at room temperature using metallic Ni7Co3 alloy nanorings as both reducing agent and sacrificial template in water. These novel alloy–Au hybrid nanorings are well biocompatible due to coating with poly(vinylpyrrolidone) and gold nanoparticles. When increasing the molar ratio of alloy to gold salt from 1:1 to 5:1, the number of the gold nanoparticles loaded on the surface of alloy nanorings were found to be decreased, and their morphology was transformed from rod to particle, remaining the ring‐like assemblies. Their saturation magnetization increased due to the ring‐like assemblies, resulting in the enhancement of the signal intensity in Spin–spin relaxation time (T2) weighted magnetic resonance imaging measurement. These alloy–Au hybrid nanocomposites can perform as multimodal imaging contrast agents for cancer cell diagnosis by two‐photon fluorescent imaging and T2‐weighted magnetic resonance imaging. In addition, their potential application for photothermal therapy was preliminarily investigated.

Meso-Cenozoic tectonics of the southern Patagonian foreland: Structural evolution and implications for Au–Ag veins in the eastern Deseado Region (Santa Cruz, Argentina)

Located in the centre of the Argentinean Patagonia between 46° and 49°S, the Deseado Region represents the foreland domain of the Southern Patagonian Andes. Its geology is characterized by thick Mesozoic sequences which, at its eastern sector, present a Mesozoic and Cenozoic geologic evolution which has been strongly determined by the development of three major tectonic phases. The present research is based on field geological mapping, interpretation of seismic and aeromagnetic data, as well as satellite image analysis. This approach has allowed us to identify and characterize the deformation that occurred throughout Jurassic, Cretaceous and Miocene times. We interpret that the most relevant structural features are the result of normal faulting generated as a response to the Jurassic rifting stage. These extensional features have strongly influenced the subsequent geometry and distribution of younger Cretaceous and Cenozoic structures. The Jurassic extensional deformation, which affected major areas of Southern Gondwana, is the product of a major intra-continental rifting stage which was accompanied by synkinematic volcanism. This tectonic regime is characterized by SW-NE directed extension that generated major oblique WNW trending faults accommodating regional dextral-extension. In the study area, this tectonic regime is inferred from the geometries of major fault systems interpreted from available seismic reflection data, as well as from the spatial distribution and orientation of the extensional fracturing associated with the opening of hybrid and dilatational siliceous epithermal Au–Ag veins. Following the Jurassic rifting stage, a more restricted Cretaceous -post-Neocomian-compressional tectonic phase took place. Throughout this period, we interpret the previously formed Jurassic extensional structures to have been reactivated under sinistral transpression. Deformation during this period generated sinistral-reverse WNW belts of deformation, which accommodated reverse faulting, imbricate thrusts, dextral and sinistral R1 and R2 shears and disharmonic folds due to a buttress effect. Under the post-Oligocene Andean regime, W–E directed compression acted on previously-formed N to NNE-oriented normal faults. Compression and shortening uplifted a series of narrow and sub-meridional ranges which run as a 200 km long inversion-related tectonic front along the Patagonian foreland. Between 47°11′ and 48°40′S, one of these NNE ranges divides the entire Deseado Region into two distinctive structural domains. Whilst the western domain presents dominant NNW morphotectonic features, that to the east appears highly dominated by WNW fabrics of Jurassic and Cretaceous age. The structural features of the Eastern domain appear to extend further north of the Deseado Region towards the vicinity of the San Jorge Gulf. This WNW-trending belt hosts pre-Upper Cretaceous rocks and pre-drift basement rocks which include igneous Paleozoic metamorphic rocks and Permian to Triassic sedimentary units. The Deseado region’s epithermal Au–Ag Jurassic vein systems result from the infilling and deposition of low temperature hydrothermal fluids within dilatational and hybrid structures. These spectacular vein systems are compatible with the regional SW-NE extension direction controlled by the Jurassic intra-continental rifting of southern Gondwana. Dilatational and hybrid veins are preferentially hosted by fractures in the Jurassic volcanic rocks, while the veins located within the pre-volcanic basement preferentially infill normal faults. Finally, most of these epithermal vein fields where exhumed during a moderate phase of inversion during Cretaceous times.

Fe(3)O(4)-Au and Fe(2)O(3)-Au Hybrid Nanorods: Layer-by-Layer Assembly Synthesis and Their Magnetic and Optical Properties.

A layer-by-layer technique has been developed to synthesize FeOOH–Au hybrid nanorods that can be transformed into Fe2O3–Au and Fe3O4–Au hybrid nanorods via controllable annealing process. The homogenous deposition of Au nanoparticles onto the surface of FeOOH nanorods can be attributed to the strong electrostatic attraction between metal ions and polyelectrolyte-modified FeOOH nanorods. The annealing atmosphere controls the phase transformation from FeOOH–Au to Fe3O4–Au and α-Fe2O3–Au. Moreover, the magnetic and optical properties of as-synthesized Fe2O3–Au and Fe3O4–Au hybrid nanorods have been investigated.

Electronic Structure of the Thiophene/Au(111) Interface Probed by Two-Photon Photoemission

The electronic structure of thiophene adsorbed on Au(111) has been investigated by two-photon photoemission (2PPE) spectroscopy and density functional theory (DFT) calculations. The dominant interfacial feature observed in the 2PPE spectra is a nondispersive unoccupied state whose width and energy (referenced to the Fermi level) decrease with increasing coverage. We assign this feature to a thiophene LUMO-derived state of mixed sulfur and carbon p−π character. DFT calculations indicate that the experimentally observed decrease in width of this state with increasing coverage is a result of weakening of the thiophene−Au(111) interaction. Increasing the molecular density forces the thiophene plane to tilt away from the surface, rotating the molecular orbitals away from an orientation more favorable for S−Au and π−Au hybridization. We attribute the ∼0.2 eV shift of the LUMO toward the Fermi level to stabilization of the transient anion due to the increasing effect of charge-induced polarization of the neighbo...

Induced SER‐Activity in Nanostructured Ag–Silica–Au Supports via Long‐Range Plasmon Coupling

AbstractA novel Ag–silica–Au hybrid device is developed that displays a long‐range plasmon transfer of Ag to Au leading to enhanced Raman scattering of molecules largely separated from the optically excited Ag surface. A nanoscopically rough Ag surface is coated by a silica spacer of variable thickness from ∼1 to 21 nm and a thin Au film of ∼25 nm thickness. The outer Au surface is further functionalized by a self‐assembled monolayer (SAM) for electrostatic binding of the heme protein cytochrome c (Cyt c) that serves as a Raman probe and model enzyme. High‐quality surface‐enhanced resonance Raman (SERR) spectra are obtained with 413 nm excitation, demonstrating that the enhancement results exclusively from excitation of Ag surface plasmons. The enhancement factor is estimated to be 2 × 104–8 × 103 for a separation of Cyt c from the Ag surface by 28–47 nm, corresponding to an attenuation of the enhancement by a factor of only 2–6 compared to Cyt c adsorbed directly on a SAM‐coated Ag electrode. Upon immobilization of Cyt c on the functionalized Ag–silica–Au device, the native structure and redox properties are preserved as demonstrated by time‐ and potential‐dependent SERR spectroscopy.

Self‐Assembly, Disassembly, and Reassembly of Gold Nanorods Mediated by Bis(terpyridine)–Metal Connectivity

Since the advent of nanotechnology, a primary challenge has been to assemble materials from predesigned building blocks for the fabrication of nanometer-sized materials. Metal nanocrystals (NCs) have attracted significant attention due to their unique shape and size, as well as their tuneable electrical, optical and catalytic properties. A bottomup approach has generally been used for constructing the desired multi-unit composites from individual components. Although extensive studies have been performed on spherically shaped NCs, research on anisotropic nanoparticles, for example, nanorods (NRs) with a distinct 1D or linear structure, is limited. Since the properties of NCs are mostly sizeand shape-dependent, NRs have the potential to show novel as well as improved properties, such as in surface-enhanced Raman scattering (SERS) effects or optical and fluorescent properties, when compared to isotropic nanospheres (NSs). c,3] Geometrically, the aspect ratio (the length of major axis divided by the width of minor axis) of NRs is >1 and their cofacial assembly produces more angularly complex structures than that of the NSs. Side-to-side assemblies of NRs have been achieved by introducing active sites on the sides of the rods and subsequently connecting via DNA, electrostatic interaction, and more recently with click chemistry; however, arrangement of NRs in an endto-end orientation, for example, forming chains or branched structures, requires a regiospecific functionalization. Toward this goal, the tips of NRs have been modified with different metals, which were subsequently termed nanodumbbells, for participation in direct end-to-end assembly. It is well-known that Au NRs have different crystallographic facets, which comprise the ends and side surfaces. Recently, it was found that these side facets have a higher surface energy, and in turn, adsorb more bilayer surfactant, for example, cetyltrimethylammonium bromide (CTAB); notably, the yield of these surface-modified nanorods has been shown to be supplier (CTAB) dependent. Current progress on direct end-to-end Au NR assembly has focused on using biocompatible connectors, a,w-dithiols, and synthetic polymers. As well, organometallic connections, such as bis(terpyridine)-transition metal complexes, are also of interest due to their potential to impart unique electrical, optical, and photovoltaic properties. For example, hybrid Au NCs and bis(terpyridine)–Ru complexes have been fabricated and shown to exhibit enhanced electrochemical properties. Herein, we report the first example of a bottom-up approach for the end-to-end linear and branched assembly of Au NRs into multicomponent structures using [(disulfide-modified terpyridine)2–M ] (M=Fe or Cd) interconnectors and their facile disassembly and reassembly. The synthesis of disulfide-modified monoterpyridine (SStpy) 2, the [(SS-tpy)2–M ] complexes 3 (M=Fe), and 4 (M= Cd) is shown in Scheme 1. In a typical Gabriel synthesis, 4’(4-hydroxyphenyl)-2,2’:6’2’’-terpyridine was treated with N-(3-bromopropyl)phthalimide to afford the intermediate protected amine, which was subsequently deprotected (H2NNH2·H2O) to give the amine-modified monoterpyridine 1. The structure was supported (H NMR) by signals for the new OCH2 (4.17 ppm) and CH2NH2 (3.20 ppm) moieties; a dominate peak (ESI-MS) at m/z 383.3 [M+H] further confirms the structure. Disulfide-modified monoterpyridine 2 [a] Y.-T. Chan, Prof. Dr. G. R. Newkome Departments of Polymer Science and Chemistry The University of Akron, Akron, OH 44325-4717 (USA) Fax: (+1)330-972-2413 E-mail : newkome@uakron.edu [b] Dr. S. Li Excel Polymers, 14330 Kinsman Rd. Burton, OH 44325 (USA) [c] Dr. C. N. Moorefield Maurice Morton Institute for Polymer Science The University of Akron, Akron, OH 44325 (USA) [d] Dr. P. Wang ChemNano Materials, 2220 High St. Suite 605 Cuyahoga Falls, OH 44221 (USA) [e] Prof. Dr. C. D. Shreiner Chemistry Department, Hiram College, P.O. Box 67 Hiram, OH 44234 (USA) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201000040.

Numerical Design Methods of Nanostructure Array for Nanobiosensing

Numerical methods are very important for designing nanodevices since localized surface plasmon resonance is sensitive to the geometric parameters. Especially, as for nano-biosensor, the proper choice of design tool is very critical in terms of the accuracy and simulation time. In this paper, we compare the discrete dipole approximation (DDA) with the finite integration technique (FIT) of the full-wave electromagnetic commercial software (CST Microwave Studio) in worldwide use with popularity. The refractive index sensitivity of rhombic hybrid Au–Ag nanostructures is calculated and compared in visible wavelength using DDA and FIT. Comparing the calculated results, the DDA has two advantages over the FIT: easy control of geometric parameter and less simulation time without compromising the accuracy. The limitations of the DDA will be deliberated as well.

The Synthesis of Gel-Like Hybrid Nanomaterials Based on Carbon Nanotube Decorated with Metal Nanoparticles at 45°C

First, the monodispersed Au nanoparticle were fabricated with adsorption role of alkane thiol. Second, the gold was coated on multi-walled carbon nanotubes (MWNTs) through electrostatic interaction between the polar group of MWNTs and alkane thiol. Finally, the gel-like MWNTs-coated Au hybrid nanomaterials were obtained by hydrogen bonding of PEO-b-PPO-b-PEO polymer. The content of MWNTs and Au was up to 23 wt%. The material was a solid at room temperature, which behaved like a gel that was molten but not flowed at 45°C. The process of gel and solidification was reversible over many cycles. It could be dispersed in water for three months due to amphiphilic properties of the modifier molecule.

Synergistic Effects on Second Harmonic Generation of Hybrid CdSe−Au Nanoparticles

Hybrid semiconductor-metal nanoparticles exhibit a combination of properties from the disparate components or even, more interestingly, synergetic properties which arise from the coupling between the two materials. In this work, we study the second harmonic generation (SHG) in CdSe-Au hybrid nanoparticles in comparison with their components, using the Hyper-Rayleigh scattering (HRS) method. Possible contribution of symmetry effects was studied by comparing symmetric two-sided gold-tipped CdSe nanodumbbells with asymmetric one-sided quantum dot-Au (QD-Au) hybrids. A simplistic view of a symmetry effect is disproved in this case by the experimental data, which shows an unexpected reduction in the SHG response in both cases, compared to the respective mixtures of Au and CdSe nanoparticles. For CdSe-Au hybrids with a long semiconductor rod segment, we find that the SHG response corresponds to a sum of the contributions from the semiconductor and the metal components. However, for QD-Au and smaller dumbbells, the SHG response is smaller than expected from a simple sum of the contribution from both components. This reduction is assigned to the effects related to the CdSe-Au interfacial region within these hybrids. A first plausible contribution to the reduction is the dephasing induced by the gold, leading to diminished SHG from the CdSe component. This reduced response of the semiconductor component is accompanied by reduced SHG from the gold component which is assigned to a partial change of the surface of the gold once an interface with CdSe is formed. These observations regarding the SHG response manifest the unique properties that arise from the combination of a semiconductor and a metal within one hybrid nanoparticle.

(InSb/GaAs)-Au hybrid macro-structure prepared by flash evaporation

n-Type indium antimonide-Au hybrid macro-structure was successfully fabricated on p-GaAs substrate by a simple and economic flash evaporation technique. The elemental composition of the prepared InSb film was confirmed by energy dispersive X-ray spectroscopy microanalysis (EDX). The surface topography and crystal structure of the InSb film was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The magnetoresistance of the prepared hybrid macro-structure was measured and discussed in terms of the model of current redistribution.

Optical Characteristics of Rhombic Hybrid Au–Ag Nanostructures Calculated by Discrete Dipole Approximation Method

The extinction spectra of rhombic hybrid Au–Ag nanostructures have been calculated using the discrete dipole approximation (DDA) aided design method. The plasmon peaks of the rhombic hybrid Au–Ag nanostructures can be tuned not only by the structural parameters but also by the effective refractive index of the medium surrounding around the nanostructures. The relationship between the extinction efficiency and the polarizations of the incident light are also analyzed by the DDA method. Based on the calculated curves, the main parameters of the nanostructure arrays such as thickness, period and the refractive index sensitivity can be determined. Using this aided method, a hybrid Au–Ag nanostructures array is designed with the determinant parameters of thickness (Au 5 nm, Ag 25 nm), period (400 nm) and the refractive index sensitivity (400 nm/RIU). This study shows that the particle material, period and the effective refractive indexes of the mediums have significant effect on the optical properties of the nanostructures, and DDA aided design method can provide the perfect structure parameters for our hybrid nanostructures. Copyright © 2010 American Scientific Publishers All rights reserved

Image dipoles approach to the local field enhancement in nanostructured Ag–Au hybrid devices

We have investigated the plasmonic enhancement in the radiation field at various nanostructured multilayer devices that may be applied in surface enhanced Raman spectroscopy. We apply an image dipole method to describe the effect of surface morphology on the field enhancement in a quasistatic limit. In particular, we compare the performance of a nanostructured silver surface and a layered silver-gold hybrid device. It is found that localized surface plasmon states provide a high field enhancement in silver-gold hybrid devices, where symmetry breaking due to surface defects is a supporting factor. These results are compared to those obtained for multishell nanoparticles of spherical symmetry. Calculated enhancement factors are discussed on the background of recent experimental data.

Reductive dissolution of Fe3O4facilitated by the Au domain of an Fe3O4/Au hybrid nanocrystal: formation of a nanorattle structure composed of a hollow porous silicananoshell and entrapped Aunanocrystal

The Fe(3)O(4) grain of a Fe(3)O(4)/Au hybrid nanocrystal encapsulated in a silica nanosphere was rapidly and exclusively dissolved through a reductive process facilitated by the attached Au grain, resulting in the formation of a nanorattle structure which has utility as a nanoreactor to template the growth of nanocrystals inside the cavity.

Towards an accurate description of the electronic properties of the biphenylthiol/gold interface: The role of exact exchange

We investigate the role of the exact exchange in describing the biphenylthiol/gold interface. The study is performed by simulating the electronic properties of mercaptobiphenylthiol and aminobiphenylthiol molecules adsorbed on a Au(23) cluster, using local, semilocal and hybrid functionals and an effective exact exchange method, namely, the localized Hartree-Fock (LHF). We find that the local/semilocal functionals strongly underestimate the charge transfer and the bond dipole at the interface due to the self-interaction-error (SIE), which alters the correct level alignment. On the other hand the LHF method is SIE free and predicts a larger charge transfer and bond dipole. We also found that LHF results can be reproduced using hybrid functionals and that conventional local/semilocal correlation functionals are unable to improve over the exchange-only description.

Self-Guided One-Sided Metal Reduction in Te Nanowires Leading to Au−Te Matchsticks

Highly anisotropic nanoscale structures are fundamentally important for understanding the properties of hybrid nanoscale systems and self-organization phenomena, but they are typically difficult to prepare experimentally. Hybrid Au and Te matchstick-like nanostructures, which display high structural anisotropy, were synthesized using small Au clusters as seeds. The matchsticks were found to be an exclusive product of this reaction. We hypothesize that the mechanism of the synthesis is based on self-directed site-specific reduction of Au ions due to the gradually increasing dipole moment facilitating this process on one side of Te nanorods, which is supported by quantum mechanical calculations.

SnO 2–Au hybrid nanoparticles as effective catalysts for oxygen electroreduction in alkaline media

SnO 2 nanoparticles were synthesized by a facile electrochemical method based on anodic oxidation of a tin metal sheet. The resulting particles, with an average diameter of about 20 nm, were then loaded with varied amounts of HAuCl 4, forming SnO 2–Au( x) ( x = 0, 0.095, 0.38, 0.76, 1.9, 3.0, and 3.8 at.%) hybrid nanoparticles after calcination at elevated temperatures (700 °C). X-ray diffraction (XRD) and transmission electron microscopic (TEM) measurements showed that the SnO 2 particles exhibited high crystallinity with a rutile structure, and spherical Au nanoparticles were dispersed on the surface of the SnO 2 support. Based on the TEM images and the width of the Au(2 0 0) XRD diffraction peak, the size of the Au nanoparticles was found to be between 15 and 35 nm in diameter and decrease with increasing loading of the original HAuCl 4 precursor. The electrocatalytic activity of the resulting SnO 2–Au( x) composite nanoparticles toward oxygen reduction reactions (ORR) was then evaluated by cyclic and rotating disk voltammetric measurements in alkaline solutions. It was found that the incorporation of gold nanoparticles led to apparent improvement of the catalytic activity of SnO 2 nanoparticles. Moreover, the ORR electrocatalytic activity exhibited a strong dependence on the gold loading in the hybrid nanoparticles, and the most active catalyst was found with a gold loading of 1.9 at.%, based on the reduction current density and onset potential of ORR. Furthermore, at this gold loading, oxygen reduction was found to follow the efficient four-electron reaction pathway, whereas at other Au loadings, the number of electron transfer involved in oxygen reduction varied between 1 and 3. Additionally, Tafel analysis suggested that at low overpotentials, the first electron transfer might be the limiting step in oxygen reduction, whereas at high potentials, oxygen adsorption appeared to play the determining role at the SnO 2–Au hybrid electrodes. These results indicate that the SnO 2–Au composite nanoparticles might serve as effective catalysts for oxygen electroreduction in alkaline media.

FUNCTIONALIZATION OF MULTI-WALLED CARBON NANOTUBES WITH CYSTEAMINE FOR THE CONSTRUCTION OF CNT/GOLD NANOPARTICLE HYBRID NANOSTRUCTURES

Combining hybrid nanostructures of metal nanoparticles (NPs) and carbon nanotubes could afford a novel strategy to prepare promising nanomaterials for the highly sensitive sensors and imaging science applications. Conventional acid oxidation process was used to obtain carboxylic acid bound multi-walled carbon nanotubes (MWNTs) which was further acylated with thionyl chloride to give acyl chloride functionalized MWNTs. Thiol functionalized MWNTs were synthesized by amidation reaction of the acylated MWNTs with cysteamine. Further, gold nanoparticles (GNPs) were successfully fabricated on the tube walls to yield the CNT/ Au hybrid. Fourier transform infrared spectroscopy and energy dispersive X-ray studies were used to characterize the surface chemical functionalities and composition of MWNTs, respectively. Evidence for the attachment of GNPs to thiol functionalized MWNTs was obtained from ultraviolet–visible absorption spectra. In addition, TEM images provided a vivid image of uniform decoration of GNPs on the nanotube sidewalls.

Localized surface plasmon resonance-based hybrid Au–Ag nanoparticles for detection of Staphylococcus aureus enterotoxin B

A triangular hybrid Au–Ag nanoparticles array was proposed for the purpose of biosensing in this paper. Constructing the hybrid nanoparticles, an Au thin film is capped on the Ag nanoparticles which are attached on glass substrate. The hybrid nanoparticles array was designed by means of finite-difference and time-domain (FDTD) algorithm-based computational numerical calculation and optimization. Sensitivity of refractive index of the hybrid nanoparticles array was obtained by the computational calculation and experimental detection. Moreover, the hybrid nanoparticles array can prevent oxidation of the pure Ag nanoparticles from atmosphere environment because the Au protective layer was deposited on top of the Ag nanoparticles so as to isolate the Ag particles from the atmosphere. We presented a novel surface covalent link method between the localized surface plasmon resonance (LSPR) effect-based biosensors with hybrid nanoparticles array and the detected target molecules. The generated surface plasmon wave from the array carries the biological interaction message into the corresponding spectra. Staphylococcus aureus enterotoxin B (SEB), a small protein toxin was directly detected at nanogramme per milliliter level using the triangular hybrid Au–Ag nanoparticles. Hence one more option for the SEB detection is provided by this way.