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The development of analytical platforms incorporating Au nanoparticles (NPs) for optical biosensing requires approaches to produce optically responsive and target selective materials. In the present work, fluorescence emission and bioselectivity of Au NPs have been combined by a one-step surface functionalization using fluorescein isothiocyanate (FITC) and biotin. First, colloidal Au NPs (d =17.7 ± 2.7 nm) exhibiting an absorption maximum ([λ.sub.max]) at 524.5 nm have been surface-modified with the polyelectrolytes (PE) poly(allylamine hydrochloride) (PAH) and poly(sodium styrene sulfonate) (PSS). Two strategies were then assessed for the functionalization of Au NPs: (i) functionalization of PAH with biotin and subsequent coating of the NPs and (ii) surface modification of the NPs with the PE followed by postfunctionalization with biotin. The effect of the surface functionalization on the colloidal NPs was monitored by optical absorption and fluorescence emission spectroscopies, dynamic light scattering (DLS), zeta potential measurements and transmission electron microscopy (TEM). Finally, the optical response and specificity of the functionalized NPs towards avidin was evaluated by optical measurements. The results have shown that these hybrid nanostructures have potential to be used in biosensing. In particular, the aggregation of biotinylated Au assemblies associated with the biorecognition of avidin could be assessed by fluorescence emission spectroscopy. Keywords Biosensor * Gold nanoparticles * Optical properties * Hybrid nanostructures * Polyelectrolytes * Biotinylation, Introduction Gold nanoparticles (Au NPs) have been widely studied for diverse bioapplications namely due to their optical properties which are dependent on the morphological characteristics and surrounding medium [1-5]. These [...]

Localized surface plasmons can modify linear optical responses of materials located in their vicinity. In particular, rare earth ions luminescence can be enhanced by gold nanoparticles. Luminescence exaltation is a complex phenomenon that depends on multiple parameters, a critical one being the coupling distance between the emitting species and the plasmonic core. An original multilayer nanostructure de-signed to precisely control the distance between the gold cores and the luminescent ions, and to study its effect on the luminescent properties is presented here. Homogeneous silica shells with controlled thicknesses adjustable from 2 to 50 nm and rare earth ion doping rates up to 2x[10.sup.20] Eu/[cm.sup.3] of silica were deposited onto gold nanospheres. These original nanostructures are then incorporated into densified solgel silica composites with high-optical quality. Luminescence properties are studied for increasing gold-europium (III) distances. Strong luminescence quenching is evidenced for coupling distances up to 28 nm. Keywords Gold nanoparticles. Coreshell nanoparticles. Luminescence exaltation. Rare earth. Silica coating. Luminescence quenching, Introduction Gold nanoparticles interact with light and exhibit strong and tunable surface plasmon resonance (SPR). These localized surface plasmons originating from gold nanoparticles in various media can enhance linear and [...]

It is well known that coupling a single emitter to metallic structures modifies drastically its fluorescence properties compared to single emitter in vacuum. Depending on various parameters such as the nature of the metal or the geometry of the metallic structure, quenching or intensity enhancement as well as radiative processes acceleration are obtained through the creation of new desexcitation channels. The use of metallic random structures gives the opportunity to magnify the effect of the coupling by strongly confined electromagnetic fields. A gold film at the percolation threshold is an interesting illustration of that effect. Here, we study the influence of the method used to realize these films through two different examples. First, we show that the mean size of the gold clusters constituting the film depends on the deposition method. Even if similar optical properties (in particular far-field absorption) are exhibited by the structures, crucial differences appear in the fluorescence of single emitters when coupled to the two kinds of random gold film. Especially, we focus our attention on the creation of desexcitation channels and show that they are cluster size dependent. Keywords Nanocrystals * Metallic random structures * Surface plasmon resonances * Purcell effect, Introduction Colloidal core-shell nanocrystals (NCs) are promising single emitters. They are synthesized in solution and so are easy to use and to prepare at low cost. They are bright (high [...]

Layers of thiophenol functionalized spherical gold nanoparticles grafted on Si(100) are probed by linear UV-vis, Fourier transform infrared and nonlinear infrared-visible vi-brational sum/difference-frequency generation spectroscopies as a function of the nanoparticles surface coverage. Depending on the dipping time (5 min, 20 min, 1 h, and 24 h) in the colloidal solution, AFM imaging corroborates that the silicon surface coverage with gold nanoparticles increases, while the distance between neighbouring nanoparticles decreases, leading to their aggregation which dramatically impacts their optical properties. In the UV-vis reflectance spectra after the appearance of the 525-nm individual plasmonic band, a second broad band located at 660 nm and related to the gold nanoparticles aggregation on silicon rapidly dominates in intensity. Nonlinear vibrational spectroscopy is able to detect the specific vibration of the thiophenol molecules (3, 055 [cm.sup.-1]) whatever the immersion time and at least down to 1 % of the substrate filling factor by the gold nanoparticles, overtaking the molecular sensitivity threshold of surface infrared and Raman spectroscopies on small gold nanostructures (17 nm) adsorbed on a semiconductor. Moreover, a quantitative analysis of the nonlinear vibrational fingerprint from 5 min to 24 h in the framework of the effective medium models of Maxwell-Garnett and Bruggeman illustrates the role played by the interband and the plasmonic properties of gold modulated by the silicon optical response. In this case, the sample reflectivity affects the molecular oscillator strength measured by nonlinear optical vibrational spectroscopy. For this latter technique, no coupling with the optical properties of aggregated AuNps is evidenced while the localized surface plasmon resonance excitation amplifies the molecular response. Keywords Gold. Nanospheres. Silicon. Nonlinear optics. UV-visible spectroscopy. Atomic force microscopy, Introduction The manufacturing of well-designed nanosensors is a key step to improve their sensitivity threshold in the probe-target scheme encountered in molecular recognition, especially when expecting the detection of materials [...]

In recent years, there has been considerable interest and research activity in using gold nanoparticle materials for biomedical applications including biomolecular detection, bioimaging, drug delivery, and photothermal therapy. In order to apply gold nanoparticles in the real biological world, we need to have a better understanding of the potential interactions between gold nanoparticle materials and biomolecules in vivo and in vitro. Here, we report the use of dynamic light scattering (DLS) for gold nanorods characterization and nanorod-protein interaction study. In the size distribution diagram, gold nanorods with certain aspect ratios exhibit two size distribution peaks, one with an average hydrodynamic diameter at 5-7 nm, and one at 70-80 nm. The small size peak is attributed to the rotational diffusion of the nanorods instead of an actual dimension of the nanorods. When proteins are adsorbed to the gold nanorods, the average particle size of the nanorods increases and the rotational diffusion-related size distribution peak also changes dramatically. We examined the interaction between four different proteins, bovine serum albumin, human serum albumin, immunoglobulin G, and immunoglobulin A (IgA) with four gold nanorods that have the same diameter but different aspect ratios. From this study, we found that protein adsorption to gold nanorods is strongly dependent on the aspect ratio of the nanorods, and varies significantly from protein to protein. The two serum albumin proteins caused nanorod aggregation upon interaction with the nanorods, while the two immunoglobulin proteins formed a stable protein corona on the nanorod surface without causing significant nanorod aggregation. This study demonstrates that DLS is a valuable tool for nanorod characterization. It reveals information complementary to molecular spectroscopic techniques on gold nanorod-protein interactions. Keywords Gold nanoparticle. Gold nanorod. Protein interaction. Dynamic light scattering, Introduction Gold nanoparticle materials have attracted considerable attention due to their unique properties and potential applications as optical probes. Within their surface plasmon resonance (SPR) wavelength region, gold nanoparticles absorb [...]

Dynamic fight scattering (DIS) is an analytical tool used routinely for measuring the hydrodynamic size of nanoparticles and colloids in a liquid environment. Gold nanopartieles (GNPs) are extraordinary light scatterers at or near their surface plasmon resonance wavelength. In this study, we demonstrate that DLS can be used as a very convenient and powerful tool for gold nanoparticle bioconjugation and biomolecniar binding studies. The conjugation process between protein A and gold nanoparticles under different experimental conditions and the quality as well as the stability of the prepared conjugates were monitored and characterized systematically by DLS. Furthermore, the specific interactions between protein A-conjugated gold nanoparticles and a target protein, human IgG, can be detected and monitored in situ by measuring the average particle size change of the assay solution. For the first time, we demonstrate that DLS is able to directly and quantitatively measure the binding stoichiometry between a protein-conjugated GNP probe and a target analyte protein in solution. 10.1021/ac901822w

An active volume scaling is carried out in bore and length of a Sr atom laser excited in a nanosecond pulsed longitudinal He-Sr[Br.sub.2] discharge. The optimal discharge conditions are provided for achieving a maximal average output power at many Sr atom and ion lines.

Surface plasmon polaritons (SPPs) are responsible for exotic optical phenomena, including negative refraction, surface enhanced Raman scattering, and nanoscale focusing of light. Although many materials support SPPs, the choice of metal for most applications has been based on traditional plasmonic materials (Ag, Au) because there have been no side-by-side comparisons of the different materials on well-defined, nanostructured surfaces. Here, we report a platform that not only enabled rapid screening of a wide range of metals under different excitation conditions and dielectric environments, but also identified new and unexpected materials for biosensing applications. Nanopyramidal gratings were used to generate plasmon dispersion diagrams for Al, Ag, Au, Cu, and Pd. Surprisingly, the SPP coupling efficiencies of Cu and AI exceeded widely used plasmonic materials under certain excitation conditions. Furthermore, grazing angle excitation led to the highest refractive index sensitivities (figure of merit >85) reported at optical frequencies because of extremely narrow SPP resonances (full-width-at-half-minimum nanophotonics | surface plasmon polariton | dispersion diagrams | chemical and biological sensing

We investigate the influence of the binding layer on the reflectance of a Au film in vacuum ultraviolet (VUV) wavelength region theoretically and experimentally. The reflectance of Au films on quartz glass substrates with an ~2 nm binding layer of Ti, Cr, and Ir are estimated and fabricated. Their reflectance in the 115-140 nm wavelength region are measured continuously by the reflectometer located in the National Synchroton Radiation Laboratory. The testing results show that the addition of the binding layer indeed greatly enhances the interfacial adhesion of the Au layer to the quartz glass substrate, but it also exerts a considerably adverse impact on the reflectance of the Au layer in VUV wavelength region. In near normal incidence, the reflectance of the Au layer with a 2 nm thick binding layer is less than 20%, ~5% lower than those without the binding layer. The material used for the binding layer has little impact on the reflectance if this layer is thin enough. OCIS codes: 310.6860, 310.3915.

The feasibility of photoacoustic (PA) flow estimation with wash-in analysis using gold nanorods as a PA contrast agent is described. Results show that the high optical absorption and scattering of tissue constituents reduces the sensitivity of detection when using gold nanorods.

The working and characteristics of a low pass x-ray polarizer, which is based on metal-dielectric-metal triple reflection configuration and suppresses the higher-order diffraction light from vacuum ultraviolet and x-ray monochromators, are described. It is found that the polarizer can easily tune the cutoff photon energy in a broadband spectral region by an appropriate optimization of material and angle of incidence.

The preparation of patterned size-selected [Au.sub.N] (N = 300-23000) clusters on various optical substrates (glass, quartz, polymethyl methacrylate, and mica) is reported. Confocal laser scanning microscopy measurements using an interferometric detection scheme validated the expected optical behavior of the deposited size-selected gold clusters governed by the well known plasmon resonance.

The study focuses on the effects of a gold bulk contamination on the performances of boron doped p-type crystalline solar cells made from contaminated silicon wafers, which varies for different base doping levels and different kinds of materials. This process is extremely useful because of its hydrogenation effects, though the presence of impurities in such materials containing large densities of defects lead to several undesired impurity-defect interactions.

Nanocomposite thin films formed by gold nanoparticles embedded in a titanium dioxide matrix are synthesized by pulsed laser deposition. The results proved the possibility of tuning the optical properties of gold-titanium dioxide nanocomposites with the choice of laser irradiation parameters.

Polyhedral gold nanocrystals with [O.sub.h] symmetry are synthesized by a modified polyol process in refluxing 1,5-pentanediol (PD). The selective growth conditions are extended to the synthesis of anisotropic nanocrystals, such as rods, wires and branched structures, displaying intriguing optical properties for biomedical applications.

The effect of geometrical parameters and metal composition on the sensitivity of the plasmon response (frequency and bandwidth) of Ag, Au, and their alloy nanorods to changes in the refractive index of the surrounding medium is investigated. The calculations show that the plasmon resonance sensitivity does not change with the metal composition and Ag, Au and Ag-Au alloy nanorods have similar sensitivity at the same size and shape.

A study shows that gold nanoparticles can be used as a contrast agent to assist quantitative blood flow estimation in photoacoustic (PA) imaging. The in vitro results have shown good linearity between the measurements and the theory, indicating the potential of relative PA flow measurements with gold nanoparticles.

A study on the optical properties of gold semicontinuous films near the percolation threshold is conducted using a scanning nearfield optical microscope (SNOM) operated in a collection/transmission mode. Local field intensity enhancements due to localized surface-plasmon-polaritons are accurately observed.

A fluorescein derivative (SAMSA) bound to gold nanoparticles of different diameters is investigated by using time resolved fluorescence at the single molecule level in a wide dynamic range, from nanosecond to second time scale. The results have revealed a strong coupling between the vibro-electronic configuration of the dye and the plasmonic features of the metal nanoparticles that provide dye radiationless deactivation channels on a wide dynamic range.

Light emission at ~415 nm was observed for gold particles with diameters of 2.6-6.0 nm dispersed in a solution containing bis(2,4,6-trichlorophenyl) oxalate and hydrogen peroxide. It was found that the light intensity was independent of the protecting reagents of the gold nanoparticles with similar size, the light intensity with gold nanoparticles of 5.0 and 6.0 nm in diameter was stronger than that with gold nanoparticles of 2.6 and 2.8 nm in diameter, and the light intensity increased linearly with the concentration of the gold nanoparticles using 6.0-nm gold nanoparticles. The gold nanoparticles were identified as emitting species, and the quantum yield was determined to be (2.8 [+ or -] 0.3) x [10.sup.-5] using 6.0-nm gold nanoparticles. The light emission is suggested to involve a sequence of steps: the oxidation reaction of bis(2,4,6-trichlorophenyl) oxalate with hydrogen peroxide yielding an energy-rich intermediate 1,2-dioxetanedione, the energy transfer from this intermediate to gold nanoparticles, and the radiative relaxation of the as-formed exited-state gold nanoparticles. The observed luminescence is expected to find applications in the field of bioanalysis owing to the excellent biocompatibility and relatively high stability of gold nanoparticles.

The use of SiO2-overcoated Au films as a substrate for PA-SPR is described. Changes in SPR angle shift upon Au nanosphere binding are investigated as a function of the SiO2 thickness.

Near-field and far-field extinction and scattering efficiencies for UV-vis-irradiated spherical gold nanoparticles of varying size is estimated as a function of the radiationwavelength. The role of quantum-size effects is explored by using several different dielectric function models.

A simple growth technique for preparation of metal-organic bilayer films consisting magnetic Gd and nonmagnetic Au metalic layers is presented. The bilayer films are an essentially nanostructured network of islands and interconnects that exhibit nonohmic I-V characteristics when measured laterally across the film using a conducting AFM tip.

In this study, damage evolution on Sm and O sublattices in gold implanted samarium titanate pyrochlore was studied by Rutherford backscattering spectroscopy and nuclear reaction analysis. The results showed that the atomic disorder on both the Sm and O sublattices increase nonlinearly with ion influence, eventually achieving a fully amorphous state.

On the basis of the mechanism of surface enhanced Raman scattering, it is shown that coherent anti-Stokes Raman scattering (CARS) of molecules attached to isolated gold nanoparticles are strongly enhanced and the signal from each particle is well localized. The surface enhanced CARS combined with a scanning system of metallic nanoprobe tip can realize high spatial resolution CARS microscopy beyond the diffraction limit of light.

Series of experiments were conducted to evaluate the stability of adsorption of aliphatic dithiocarboxylic acids (ADTCAs) self-assembled monolayers (SAMS) on gold. These materials found the applications where temporary nanoscale coatings are needed.

Au(super omicron) was produced at 77k by gamma-irradiation, of MTHF solution containing Au(super +). The steady state emission and excitation spectra were measured by photoexcitation at 73 K before and after gamma-irradiation of the solid solutions containing [Au(super +)] ions.

Study of the self-assemble of Hs-Pc and its application as a hole injection material in OLEDs is presented. Phthalocyanine monolayer-modified gold substrates showed high efficiency as anodes for organic light-emitting diodes.

Laser-assisted size-reduction and network formation of gold nanoparticles were performed in pure water and in a sodium dodecyl sulfate (SDS) solution and the mechanisms were studied by applying optical absorption spectroscopy and electron microscopy. Results reveal that the laser-assisted size reduction and network formation of gold nanoparticles is a promising method for preparing nanoscale devices consisting of nanoparticles and nanowires with a desired size.

The study focuses on characterizing the packing structure variation of alkanethiol gradients, and then developing RGD (Arg-Gly-Asp) containing gradients, which are mapped by Fourier transform infrared external reflection spectroscopy (FTIR-ERS). This study has important implications for the study of cellular motility and haptotactic behavior.

Self-assembled monolayers of electron donor tetramethyl xylyl dithiol (TMXYL) are synthesized and chemically switched to a conducting state by reaction with an electron acceptor tetracyanoethylene (TCNE). Low bias conductance measurements obtained by scanning tunneling spectroscopy under ultrahigh vacuum conditions reveals a significant change from insulating to ohmic behavior.

The formation of MoO3 and its spontaneous spread over an Au (111) surface is studied by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). O2 and NO2 oxidations of Mo clusters deposited on Au (111) via Mo(CO)6 CVD are compared. The results indicate that the Mo clusters on Au are probably encapsulated by gold.

The gold nanoparticles were produced by femtosecond laser ablation of a gold metal plate in an aqueous solution of alpha-cyclodextrins (CD), beta-CD, or gamma-CD. The size distribution of the nanoparticles measured by transmission electron microscopy (TEM) shifted to a drastically smaller size of ~2-2.4 nm and narrower size distribution of less than 1-1.5 nm fwhm with an increase in the concentration of cyclodextrin.

The light emission decay in bare gold particles by using the fluorescence up-conversion technique is reported. The results indicate that a weak light emission from relatively large gold nanoparticles is attributable to the interactions between surface plasmons and incident photons that occur simultaneously with the thermal electron relaxation.

The absorption properties of molecules adsorbed on single gold and silver nanoparticles are investigated, with particular emphasis on an examination of the effect on the spectrum of the absorbate. A number of absorbates studied are similar to those reported in surface-enhanced Raman scattering.

The experimental observation of electronic Raman scattering between image potential surface states is described and is observed from roughened Au and Ag surfaces covered with long-chain alkanethiol self-assembled monolayers. Models potential incorporating step edge surface roughness features indicate that the image state electron resides within or near the sulfur headgroup layer.

Ordered protein assembly, high stability and sensitivity and fast controllable electronic transfer is indicated. These properties can hold a perspective for electronic mapping of single redox protein molecules.

Near edge x-ray absorption fine structure (NEXAFS) and the density functional theory (DFT) calculation are used to study the interaction of 1-epoxy-3-butene(EpB) with Ag(110) surface. The results demonstrate the importance of both theory and experiment in determining the identity, structure, and reactivity of complex surface intermediates such as the newly discovered oxametallacycles.

The homogenous films of Au@SiO(sub 2) particles are deposited on glass as a prototype 3D 'artificial solid' with the help of the LBL method. The films are found to be uniform, colorful and had metallic reflections at low angles of incidence, even at low volume fractions.

The recent progress towards characterizing electron transport in gold nanoparticles as a function of capping ligand charge state is highlighted. Single electron tunneling energies can be manipulated predictably via pH-induced charged changes of surface bound thiol capping ligands.

The adsorption behavior of 1,3-propanedithiol (1,3-PDT) on a colloidal gold surface is investigated by means of surface-enhanced Raman scattering (SERS). The study discuses that a separate ellipsometry measurement revealed that a best one and one-half layered film could be assembled on gold in polar and protic solvents while up to three layers were assembled on gold in n-hexane solution of 1,3-PDT.

Low-voltage tetracene-based photo thin-film transistors (TFTs) with thin poly-4-vinylphenol (PVP)/Al[O.sub.x] bilayer dielectric was fabricated. It was seen that when two electrodes of Au and semitransparent Ni[O.sub.x] were adopted for source/drain, the tetracene based TFTs with Ni[O.sub.x] exhibited higher field mobility than those with Au due to the band alignment advantage of Ni[O.sub.x] over Au.

The shape-controlled evolution and in-situ stabilization of gold nanoparticles using several well-known beta-diketone chelating agents is reported. The generalization of the new strategy for realizing ligand-stabilized shape-selective gold nanoparticles that finds wide application in nanomaterial synthesis, catalysis and nanoelectronics is described.

A paradigm for tuning the optical properties of gold nanorods by organizing them longitudinally using thioalkylcarboxlic acid based bifunctional molecules is reported. A generalized procedure for uniaxial plasmon coupling through longitudinal self-assembly of Au nanorods, initially to dimers and further to linear assemblies, is presented.

The colloidal gold nanoparticles with a broad size distribution are prepared with the help of laser ablation of a gold metal plate in an aqueous solution of sodium dodecyl sulfate (SDS). Laser ablation in combination with the laser-induced size control provides a versatile full physical preparation method of size-selected gold nanoparticles.

The article explains the synthesis of an unprecedented luminescent polynuclear gold (I) [[mu].sub.3]-sulfido cluster, which is shown to exhibit a thiacrown-like architecture. The addition of [CH.sub.3]CN compound is shown to lead to numerous binding and spectroscopic changes in the system.

The interplay observed between the metal nanoparticles and dielectric spacing layers during the growth of the granular Au/[Si.sub.3][N.sub.4] multilayers grown by vapor deposition method is analyzed. An increase in the thickness of the deposited Au per bilayer in the system is shown to lead to a significant enhancement in its crystalline order.