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Abstract: We present a process for the phase-transfer of gold nanoparticles from an aqueous to an organic medium with normal alkanethiols. This method can be applied not only to large nanospheres (d ∼100nm) but also to anisotropic nanoparticles like nanorods and nanoplates. It allows the comparison of the nanoparticle optical properties when they are dispersed in both aqueous and organic media. [Copyright &y& Elsevier]

Abstract: This paper describes a performance of precise control of shell thickness in silica-coating of Au nanoparticles based on a sol–gel process, and an investigation into X-ray imaging properties for the silica-coated Au (Au/SiO2) particles. The Au nanoparticles with a size of 16.9±1.2nm prepared through a conventional citrate reduction method were used as core particles. The Au nanoparticles were silica-coated with a sol–gel reaction using tetraethylorthosilicate (TEOS) as a silica source, sodium hydroxide (NaOH) as a catalyst, and (3-aminopropyl) trimethoxysilane (APMS) as a silane coupling agent. An increase in TEOS concentration resulted in an increase in shell thickness. Under certain concentrations of Au, H2O, NaOH, and APMS, the Au/SiO2 particles with silica shell thickness of 6.0–61.0nm were produced with varying TEOS concentration. Absorption peak wavelength of surface plasmon resonance of the Au/SiO2 colloid solution depended on silica shell thickness, which agreed approximately with the predictions by Mie theory. The as-prepared colloid solution could be concentrated up to an Au concentration of 0.19M with salting-out and centrifugation. The concentrated colloid solution showed an X-ray image with high contrast, and a computed tomography value for the colloid solution with an Au concentration of 0.129M was achieved 1329.7±52.7HU. [Copyright &y& Elsevier]

Abstract: We report quantitative measurement of heat generation in Au-nanoparticle colloidal solutions induced by radiofrequency (RF) electromagnetic waves (13.56MHz; 25W). The possible role of Au nanoparticles in RF heating was systematically investigated by separating the metal nanoparticles away from the colloidal solutions by centrifugation. Contrary to the previously made assumption in this field, it is found that Au nanoparticles do not contribute to RF energy absorption. The electrical conductivity measurement of the solutions with and without Au nanoparticles reveals that the Joule heating via ionic conduction in the electrolyte solutions is the dominant mechanism of RF-radiation-to-thermal conversion. [Copyright &y& Elsevier]

Abstract: Detailed exploratory and mechanistic investigations on spontaneous formation of dye-functionalized gold nanoparticles (GNPs) using dye-based reverse micellar systems are described in this publication. The accumulated results from spectroscopic and microscopic investigations demonstrated that water molecules confined within nanoscopic enclosure of the self-assembled reverse micelles played critical role in the redox processes of aurate ions to produce GNPs, which are assumed to have approximately constant size distributions. The resulting dye-functionalized GNPs were found to offer their absorption and fluorescence emission tunability by changing the medium polarity as well as to exhibit excellent film-forming properties to give optically homogeneous polystyrene thin films. These key findings in addition to broad applicability of the self-assembling process with a variety of dye analogues have led to a conclusion that the protocol presented here serves as a versatile synthetic method to provide a potential convenience for future development of new organic–inorganic hybrid nanomaterials. [Copyright &y& Elsevier]

Abstract: Self-assembled poly(4-vinylpyridine)-grafted gold (Au) nanoparticles (NPs) and polystyrene-b-poly(4-vinylpyridine) block copolymers were fabricated by the introduction of a selective solvent to a common solution. The assembled mixtures were spin-coated onto solid substrates to fabricate composite gold/polymer thin films composed of copolymer-hybridized Au NPs and independent copolymer micelles. The obtained composite Au thin films had variable localized surface plasmon resonance (LSPR) bands and microscopic morphologies upon vapor annealing with selective solvents because the adsorption and dissolving of solvent molecules into the films could rearrange the copolymer block. The hybrid nanostructured Au thin films may have potential in vapor sensing and organic assays. [ABSTRACT FROM AUTHOR]

Abstract: A surface plasmon resonance biosensor based on ZnO–Au nanocomposites was developed for the detection of rabbit IgG. The ZnO–Au nanocomposites can bind protein by covalent attachment to construct a probe for target analyte. The probe with unique optical properties and good biocompatibility could enhance the sensitivity of SPR biosensor. Under the optimized conditions, the biosensor based on ZnO–Au nanocomposites exhibits a satisfactory response to rabbit IgG in the concentration range of 0.15–20.00μgml−1. For comparison, the biosensor based on Au film and the biosensor based on Au nanoparticles were also studied for the detection of rabbit IgG. The biosensor based on Au film shows a response to rabbit IgG in the concentration range of 2.50–20.00μgml−1. The biosensor based on Au nanoparticles shows a response in the concentration range of 0.30–20.00μgml−1. The biosensor based on ZnO–Au nanocomposites was therefore found to be the most sensitive of the three types of biosensors. The lowest concentration of rabbit IgG that can be determined by the proposed biosensor is about 16-fold lower than that of the biosensor based on Au film alone. [ABSTRACT FROM AUTHOR]

Abstract: The interactions of a biomolecule glutathione (GSH) with citrate-capped gold nanoparticles (AuNP) have been investigated to evaluate the viability of a rapid GSH-capture by gold nanoparticle carriers, as a model system for applications ranging from designing nanoparticle-enhanced functional biosensor interfaces to nanomedicine. The measurements, performed using resonance elastic light scattering (RELS) spectroscopy, have shown a strong dependence of GSH-induced scattering cross-section on gold nanoparticle size. A large increase in RELS intensity after injection of GSH, in a short reaction time (τ =60s), has been observed for small AuNP (5nm dia.) and ascribed to the fast ligand-exchange followed by AuNP assembly. The unexpected non-Langmuirian concentration dependence of scattering intensity for AuNP5nm indicates on a 2D nucleation and growth mechanism of the ligand-exchange process. The ligand-exchange and small nanoparticle ensemble formation followed by relaxation have been observed in long term (10h) monitoring of GSH–AuNP interactions by RELS. The results of molecular dynamics and quantum mechanical calculations corroborate the mechanism of the formation of hydrogen-bonded GSH-linkages and interparticle interactions and show that the assembly is driven by multiple H-bonding between GSH-capped AuNP and electrostatic zwitterionic interactions. The RELS spectroscopy has been found as a very sensitive tool for studying interparticle interactions. The application of RELS can be expanded to monitor reactivities and assembly of other monolayer-protected metal clusters, especially in very fast processes which cannot be followed by other techniques. [ABSTRACT FROM AUTHOR]

Abstract: Gold nanoprisms with average edge size of ∼140nm and thickness of ∼8nm were achieved in high-purity (∼97%) by exploiting the electrostatic aggregation and shape effects through a modified seed-mediated approach. The proposed strategy lies in the dramatically different stability and aggregation potential between the produced gold nanoprisms and spherical gold nanoparticles, which can be modulated by varying the anion concentration in the reaction solution. Hence, the gold nanoprisms spontaneously aggregated into precipitate whereas most of the spherical ones were still kept in the solution. Moreover, this strategy is also flexible enough that ultra-small gold nanoprisms with average width less than 50nm can be collected in good-purity. The structure and optical properties of these nanoprisms have been studied by TEM, SAED, XRD and UV–vis–NIR spectroscopy, respectively. These high-purity colloidal gold nanoprisms exhibit remarkably enhanced surface plasmon resonance (SPR) as well as strong near-infrared absorption. Furthermore, we have also investigated their potential for biosensing based on the sensitive changes of SPR band induced by the antibody–antigen recognition events. The experimental results clearly suggest that gold nanoprisms can be a promising nanostructured system for plasmonic sensor applications. [Copyright &y& Elsevier]

Abstract: Colloidal gold has been used as a label in sandwich assays for human IgG, in which intercalating N-[tris(hydroxymethyl)methyl]acrylamide (pTHMMAA) polymers have been employed to stabilise the particles coated with antibody fragments. A direct absorbance reading of the particles could be obtained from sandwich assays on polystyrene, and a strongly amplified response was observed in similar assays based on Surface Plasmon Resonance (SPR): for h-IgG, detection limits below 100pg/mL could be achieved. Three different polymer lengths and two different particles sizes were compared in sandwich assays performed on polystyrene and gold. The resulting binding curves fitted well to the Langmuir–Freundlich isotherm and the binding constants were in good agreement with the values found in earlier studies. The amplification afforded by the nanoparticles was strongly dependent on the antigen concentration, on the type of polymer and on the particle size. Compared to the direct response of the antigen, amplification factors larger than 100 could be achieved. The study proves that the polymers give stabilised particles, which can be used in highly sensitive sandwich assays. [Copyright &y& Elsevier]

Abstract: An aqueous suspension of gold nanoparticles of sizes from 20 to 90nm can be conjugated with mercaptosuccinic acid and exposed to a second phase of toluene containing an electrostatic coupler, tetraoctylammonium bromide, to organize the gold particles at the interface between water and toluene. The particles have an amphiphilic character similarly to Janus beads. The thus formed membrane can be transferred to a solid surface to yield centimeter-sized densely packed particle layers. We show that by changing the coupler concentration, the particle distances can be tailored, which modifies the optical properties. [Copyright &y& Elsevier]

Abstract: This paper described a facile method for preparation of gold nanoparticles with high efficient SERS activity within short reaction time in the presence of an environmentally benign and low-cost reagent named inositol hexaphosphate (IP6). IP6 acted as a tunable cross-linker to obtain a suitable separation (about 2nm) between the neighboring particles for certain surface plasmons by adjusting the dosages of IP6. When the molar ratio of Au to IP6 was 10:1, gold particles presented in nano-pearl-necklace pattern, demonstrating the high enhancement factor (>107) for 2-mercaptopyridine (2-Mpy) Raman scattering and high stability (>2months). [Copyright &y& Elsevier]

Abstract: In this study, we demonstrated a simple, efficient, and low-cost method to fabricate large-area self-assembly Au nanoparticles (AuNPs) encapsulated within silica nanofibers (Au/SiO2). The method is based on electrospinning and thermal decomposition of hybrid nanofibers prepared from the solution of tetraethylorthosilicate (TEOS), polyvinylpyrrolidone (PVP) and AuNPs. This study employed the electrospinning technique for the first time as a successful method for preparing a self-organized AuNP peapod chain in a silica nanofiber matrix, under mild conditions. It has the advantage of easily controlling the diameters of the silica nanofibers as well as the concentration of the AuNPs in the spinning solution. The Au/SiO2 hybrid nanofibers fabricated by this method exhibited an obvious photoelectric response under the illumination wavelength around the Au/SiO2 nanofibers surface plasmon resonance (SPR) absorption band, whereas no photoelectric response was observed for the pure silica fibers. The excellent characteristics of photoelectric response suggest that the electrospinning technique has a great potential for large-scale fabrication of functional nanofiber devices. The ability of coupling light responses into the nanosystems dependent on metallic nanoparticle SPR opens up new prospects for the construction of nanoscale waveguiding devices, sensors and optoelectronics. [Copyright &y& Elsevier]

Abstract: The application of localized surface plasmon resonance (LSPR) of gold nanoparticles for the detection of biotin–streptavidin binding, as a typical biological reaction, was investigated by using optical waveguide spectroscopy, and two different modes for the use of gold nanoparticles, one as a probe and the other as a label were compared with each other. The combination with optical waveguide spectroscopy was found to bring about a high sensitivity for the biomolecular detection system using LSPR of gold nanoparticles in both modes. In particular, the mode using gold nanoparticles as a label was demonstrated to be of advantage to devising proper procedures for using nanoparticles and evaluating actual response relevant to the phenomenon concerned, and thus to sensitive detection. [Copyright &y& Elsevier]

Abstract: Polymers of 2-(2-methoxyethoxy)ethyl methacrylate (MDM) were prepared by atom transfer radical polymerization using 2-(2′-bromoisobutyroyloxy)ethyl disulfide as initiator. An aqueous solution of the disulfide-carrying polymer (DT-PMDM) turned to be opaque above certain temperature (22 °C for DT-PMDM ()), which was corresponding to the lower critical solution temperature (LCST) of the polymer. The disulfide-carrying polymer could be accumulated on the surface of gold colloid as a polymer brush as confirmed by the increase in absorbance at 550 nm ascribable to the localized surface plasmon resonance (LSPR). Furthermore, the polymer brush could also be constructed on a monolayer of colloidal gold that had been deposited on a glass plate beforehand. The PMDM brush on both the free and surface-confined gold colloids showed definite temperature responsiveness in the absorbance at 550 nm. Moreover, non-specific adsorption of various proteins to the surface of polymer brush on the glass plate was examined by the absorption increase at 550 nm. The PMDM brush, which had been prepared with the DT-PMDM pretreated with NaBH4, did not adsorb lysozyme significantly below the LCST of the polymer chain, whereas substantially adsorbed the protein above the LCST. These results suggest usability of the polymer brushes with pendent ω-methoxy oligo(ethylene glycol) groups to coat various materials for biomedical applications. [Copyright &y& Elsevier]