Spontaneous deposition of gold nanoparticle nanocomposite on polymer surfaces through sol-gel chemistry

A aminosilica nanocomposite layer containing a monolayer of gold nanoparticles (d = 18-22 nm) with a well-defined spacing was spontaneously deposited on an unmodified polystyrene surface via a sol-gel reaction when the reduction reaction was carried out under 1:8 molar ratio (gold(III):aminosilane). The amount of aminosilica and spacing between gold nanoparticles were found to be a function of the aminosilane:water molar ratio, which contributes to the plasmonic property of the films with its absorption wavelength ranging between 701 and 548 nm. Furthermore, the nanocomposite film that consists of a monolayer of nanoparticles in aminosilica has also been deposited on the surface of polystyrene beads. This core-shell structure was found capable of storing electrostatic charges and forming a well-separated 2D array.     

Au–ZnO Nanocomposite Films for Plasmonic Photocatalysis

Nanocomposites based on plasmonic nanoparticles and metal‐oxide semiconductors are emerging as promising materials for conversion of solar energy into chemical energy. In this work, a Au–ZnO nanocomposite film with notably enhanced photocatalytic activity is successfully prepared by a single‐step process. Both ZnO and Au nanoparticles are synthesized in situ during baking of the film spin‐coated from a solution of Zn(CH₃COO)₂ and HAuCl₄. Furthermore, it is shown that this precursor solution can be formulated as a nanoink for the generation of micropatterns by microplotter printing, opening the way for the miniaturization of devices with enhanced properties for photocatalysis, optoelectronics, and sensing. The study demonstrates that Au–ZnO films exhibit 4.5‐fold enhanced photocatalytic properties for the decomposition of methyl orange upon sunlight exposure in comparison with ZnO films. Au nanoparticles improve significantly the photocatalytic activity of ZnO because they act as photosensitizers, absorbing photons at the localized surface plasmon resonance range (500–600 nm) and transferring electrons to the nearby ZnO semiconductor. XPS analysis of the Au–ZnO nanocomposite supports this explanation, indicating strong interactions between Au and ZnO.     

Refractive index of silver nanoparticles dispersed in polyvinyl pyrrolidone nanocomposite

A silver nanoparticles/polymer composite was fabricated by reduction of silver nitrate in the presence of the polymer polyvinyl pyrrolidone. The plasmonic resonance of silver nanoparticles leads to a remarkable change of the dielectric dispersion of the polymer in the visible range. The refractive indexes of the nanocomposite with different fractions of the precursor silver nitrate at the wavelengths of 488, 532, and 633 nm were investigated by using reflectometry. At a fraction larger than 0.122, the refractive index change was larger than 0.1, and the maximal refractive index change of 0.84 was achieved at a wavelength of 488 nm with a fraction of 0.422. The experimental results were consistent with the prediction of Maxwell Garnett theory. The solid-state nanocomposite with a strong refractive index dispersion and tunability has promising applications in optics and communication devices.     

Effect of a thin <Emphasis Type="Italic">a</Emphasis>-SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>: H film on plasmonic properties of gold nanoparticles

Data on the optical properties of a nanocomposite material constituted by gold nanoparticles covered with a thin film of amorphous hydrogenated silicon suboxide have been obtained for the first time. The thin film was deposited by gas-jet electron-beam plasma chemical-vapor deposition. As gold particles situated on the surface of quartz glass are covered with a thin a-SiO _x : H film, their plasmonic resonance peak is shifted to longer wavelengths. The calculations made in the study demonstrated a good agreement with the experiment.     

Low noise patch‐clamp current amplification by nanoparticles plasmonic–photonic coupling (analysis and modelling)

In this article, a patch‐clamp low noise current amplification based on nanoparticles plasmonic radiation is analyzed. It is well‐known, a very small current is flowing from different membrane channels and so, for extra processing the current amplification is necessary. It is notable that there are some problems in traditional electronic amplifier due to its noise and bandwidth problem. Because of the important role of the patch‐clamp current in cancer research and especially its small amplitude, it is vital to intensify it without adding any noises. In this study, the current amplification is performed firstly: from the excitement of nanoparticles by the patch‐clamp pico‐ampere current and then, the effect of nanoparticles plasmonic far‐field radiation on conductor''s carriers, which will cause the current amplification. This relates to the plasmonic‐photonic coupling and their effect on conductor carriers as the current perturbation agent. In the steady state, the current amplification can reach to 1000 times of initial level. Furthermore, we investigated the nanoparticles morphology changing effect such as size, nanoparticles inter‐distance, and nanoparticles distance from the conductor on the amplifier parameters. Finally, it should note that the original aim is to use nanoparticles plasmonic engineering and their coupling to photonics for output current manipulating.Inspec keywords: nanoparticles, plasmonics, biomembranes, low noise amplifiers, cancer, bioelectric phenomena, nanomedicine, biomedical electronicsOther keywords: output current manipulation, NP plasmonic engineering, amplifier parameters, NP morphology changing effect, steady state, current perturbation agent, conductor carrier effect, NP plasmonic far‐field radiation effect, patch‐clamp picoampere current, bandwidth problem, noise, traditional electronic amplifier, membrane channels, nanoparticle plasmonic radiation, nanoparticle plasmonic‐photonic coupling analysis, low noise patch‐clamp current amplification     

Building plasmonic nanostructures with DNA

Plasmonic structures can be constructed from precise numbers of well-defined metal nanoparticles that are held together with molecular linkers, templates or spacers. Such structures could be used to concentrate, guide and switch light on the nanoscale in sensors and various other devices. DNA was first used to rationally design plasmonic structures in 1996, and more sophisticated motifs have since emerged as effective and versatile species for guiding the assembly of plasmonic nanoparticles into structures with useful properties. Here we review the design principles for plasmonic nanostructures, and discuss how DNA has been applied to build finite-number assemblies (plasmonic molecules), regularly spaced nanoparticle chains (plasmonic polymers) and extended two- and three-dimensional ordered arrays (plasmonic crystals).     

Optothermal escape of plasmonically coupled silver nanoparticles from a three-dimensional optical trap

We demonstrate that optical trapping of multiple silver nanoparticles is strongly influenced by plasmonic coupling of the nanoparticles. Employing dark-field Rayleigh scattering imaging and spectroscopy on multiple silver nanoparticles optically trapped in three dimensions, we experimentally investigate the time-evolution of the coupled plasmon resonance and its influence on the trapping stability. With time the coupling strengthens, which is observed as a gradual red shift of the coupled plasmon scattering. When the coupled plasmon becomes resonant with the trapping laser wavelength, the trap is destabilized and nanoparticles are released from the trap. Modeling of the trapping potential and its comparison to the plasmonic heating efficiency at various nanoparticle separation distances suggests a thermal mechanism of the trap destabilization. Our findings provide insight into the specificity of three-dimensional optical manipulation of plasmonic nanostructures suitable for field enhancement, for example for surface-enhanced Raman scattering.     

Nanoarray-based biomolecular detection using individual Au nanoparticles with minimized localized surface plasmon resonance variations

Here, we present a mean to expand the use of individual metallic nanoparticles to two-dimensional plasmonic nanoarrays. An optical detection platform to track down localized surface plasmon resonance (LSPR) signals of individual nanoparticles on substrates was built for the application of plasmonic nanoarrays. A pseudoimage of nanoparticles on a substrate was reconstructed from their scattering spectra obtained by scanning a user-defined area. The spectral and spatial resolutions of the system were also discussed in detail. Most importantly, we present a method to normalize the localized surface plasmon resonance from geometrically different nanoparticles. After normalization, plasmonic responses from different particles become highly consistent, creating well-fitted dose-response curves of both surrounding refractive index changes and receptor-analyte binding to the surface of individual nanoparticles. Finally, the proof-of-concept system for plasmonic nanoarray detection is demonstrated by the measurement of the aptamer-thrombin binding event.     

Plasmonic Graphene Transparent Conductors

Plasmonic graphene is fabricated using thermally assisted self‐assembly of silver nanoparticles on graphene. The localized surface‐plasmonic effect is demonstrated with the resonance frequency shifting from 446 to 495 nm when the lateral dimension of the Ag nanoparticles increases from about 50 to 150 nm. Finite‐difference time‐domain simulations are employed to confirm the experimentally observed light‐scattering enhancement in the solar spectrum in plasmonic graphene and the decrease of both the plasmonic resonance frequency and amplitude with increasing graphene thickness. In addition, plasmonic graphene shows much‐improved electrical conductance by a factor of 2–4 as compared to the original graphene, making the plasmonic graphene a promising advanced transparent conductor with enhanced light scattering for thin‐film optoelectronic devices.     

Plasmonic Light Trapping in Thin-film Silicon Solar Cells with Improved Self-Assembled Silver Nanoparticles

Plasmonic metal nanoparticles are of great interest for light trapping in thin-film silicon solar cells. In this Letter, we demonstrate experimentally that a back reflector with plasmonic Ag nanoparticles can provide light-trapping performance comparable to state-of-the-art random textures in n-i-p amorphous silicon solar cells. This conclusion is based on the comparison to high performance n-i-p solar cell and state-of-the-art efficiency p-i-n solar cells deposited on the Asahi VU-type glass. With the plasmonic back reflector a gain of 2 mA/cm(2) in short-circuit current density was obtained without any deterioration of open circuit voltage or fill factor compared to the solar cell on a flat back reflector. The excellent light trapping is a result of strong light scattering and low parasitic absorption of self-assembled Ag nanoparticles embedded in the back reflector. The plasmonic back reflector provides a high degree of light trapping with a haze in reflection greater than 80% throughout the wavelength range 520-1100 nm. The high performance of plasmonic back reflector is attributed to improvements in the self-assembly technique, which result in a lower surface coverage and fewer small and irregular nanoparticles.     

Precisely Size‐Tunable Monodisperse Hairy Plasmonic Nanoparticles via Amphiphilic Star‐Like Block Copolymers

In situ precision synthesis of monodisperse hairy plasmonic nanoparticles with tailored dimensions and compositions by capitalizing on amphiphilic star‐like diblock copolymers as nanoreactors are reported. Such hairy plasmonic nanoparticles comprise uniform noble metal nanoparticles intimately and perpetually capped by hydrophobic polymer chains (i.e., “hairs”) with even length. Interestingly, amphiphilic star‐like diblock copolymer nanoreactors retain the spherical shape under reaction conditions, and the diameter of the resulting plasmonic nanoparticles and the thickness of polymer chains situated on the surface of the nanoparticle can be readily and precisely tailored. These hairy nanoparticles can be regarded as hard/soft core/shell nanoparticles. Notably, the polymer “hairs” are directly and permanently tethered to the noble metal nanoparticle surface, thereby preventing the aggregation of nanoparticles and rendering their dissolution in nonpolar solvents and the homogeneous distribution in polymer matrices with long‐term stability. This amphiphilic star‐like block copolymer nanoreactor‐based strategy is viable and robust and conceptually enables the design and synthesis of a rich variety of hairy functional nanoparticles with new horizons for fundamental research on self‐assembly and technological applications in plasmonics, catalysis, energy conversion and storage, bioimaging, and biosensors.     

Thermochromic nanocrystalline Au-VO2 composite thin films prepared by radiofrequency inverted cylindrical magnetron sputtering

Highly crystalline Au-VO₂ nanocomposite thin films were prepared on Corning glass substrates by reactive radiofrequency inverted cylindrical magnetron sputtering (ICMS). It is a low cost potential coating technology for the production of large area uniform nanocomposite thin films exhibiting plasmonic properties. This paper reports the synthesis and feasibility of reliably reproduced high quality of Au-VO₂ by ICMS. Structural, morphological, interfacial analysis and optical properties of synthesized Au-VO₂ nanocomposite thin films are reported.     

Embedded layer of Ag nanoparticles prepared by a combined PECVD/PVD process producing SiOxCy-Ag nanocomposite thin films

Structural properties of SiO(x)C(y)-Ag nanocomposite thin films prepared by a dual process PVD-PECVD in the same reactor have been investigated. The experimental results have demonstrated the influence of a PECVD process carried out at room temperature for the growth of a dielectric matrix on the size and the distribution density of Ag nanoparticles (NPs) deposited beforehand by magnetron sputtering. The plasma during the growth of the encapsulation SiO(x)C(y) layer caused a diffusion of silver from NPs through the SiO(x)C(y) matrix associated with a decrease in the average size of nanoparticles and an increase of their distribution density. Silver diffusion is blocked at a barrier interface to form a buried layer of individual Ag NPs which, for instance, can find plasmonic applications. Silver also diffuses toward the outer surface inducing antibacterial properties. In both cases initial Ag NPs act as reservoirs for multifunctional properties of advanced nanostructured films.     

Direct writing of large-area plasmonic photonic crystals using single-shot interference ablation

We report direct writing of metallic photonic crystals (MPCs) through a single-shot exposure of a thin film of colloidal gold nanoparticles to the interference pattern of a single UV laser pulse before a subsequent annealing process. This is defined as interference ablation, where the colloidal gold nanoparticles illuminated by the bright interference fringes are removed instantly within a timescale of about 6 ns, which is actually the pulse length of the UV laser, whereas the gold nanoparticles located within the dark interference fringes remain on the substrate and form grating structures. This kind of ablation has been proven to have a high spatial resolution and thus enables successful fabrication of waveguided MPC structures with the optical response in the visible spectral range. The subsequent annealing process transforms the grating structures consisting of ligand-covered gold nanoparticles into plasmonic MPCs. The annealing temperature is optimized to a range from 250 to 300?°C to produce MPCs of gold nanowires with a period of 300 nm and an effective area of 5 mm in diameter. If the sample of the spin-coated gold nanoparticles is rotated by 90° after the first exposure, true two-dimensional plasmonic MPCs are produced through a second exposure to the interference pattern. Strong plasmonic resonance and its coupling with the photonic modes of the waveguided MPCs verifies the success of this new fabrication technique. This is the simplest and most efficient technique so far for the construction of large-area MPC devices, which enables true mass fabrication of plasmonic devices with high reproducibility and high success rate.     

Precision Synthesis: Designing Hot Spots over Hot Spots via Selective Gold Deposition on Silver Octahedra Edges

A major challenge in plasmonic hot spot fabrication is to efficiently increase the hot spot volumes on single metal nanoparticles to generate stronger signals in plasmon‐enhanced applications. Here, the synthesis of designer nanoparticles, where plasmonic‐active Au nanodots are selectively deposited onto the edge/tip hot spot regions of Ag nanoparticles, is demonstrated using a two‐step seed‐mediated precision synthesis approach. Such a “hot spots over hot spots” strategy leads to an efficient enhancement of the plasmonic hot spot volumes on single Ag nanoparticles. Through cathodoluminescence hyperspectral imaging of these selective edge gold‐deposited Ag octahedron (SEGSO), the increase in the areas and emission intensities of hot spots on Ag octahedra are directly visualized after Au deposition. Single‐particle surface‐enhanced Raman scattering (SERS) measurements demonstrate 10‐fold and 3‐fold larger SERS enhancement factors of the SEGSO as compared to pure Ag octahedra and non‐selective gold‐deposited Ag octahedra (NSEGSO), respectively. The experimental results corroborate well with theoretical simulations, where the local electromagnetic field enhancement of our SEGSO particles is 15‐fold and 1.3‐fold stronger than pure Ag octahedra and facet‐deposited particles, respectively. The growth mechanisms of such designer nanoparticles are also discussed together with a demonstration of the versatility of this synthetic protocol.     

Ion beam surface nanostructuring of noble metal films with localized surface plasmon excitation

Noble metal nanoparticles strongly adhered to dielectric matrices have been extensively studied because of their potential applications in plasmonic devices based on tunable localized surface plasmon (LSP) excitation. Compared with conventional synthesis methods, the noble metal nanoparticles formed by ion-beam irradiation draw significant interest in recent years because a single layer dispersion of nanoparticles strongly bonded on the dielectric substrate can be obtained. In this paper, important phenomena related to ion-beam surface nanostructuring including ion-induced reshaping of metal nanoparticles, ion-induced core-satellite structure formation, and ion-induced burrowing of these nanoparticles are discussed, with their individual effects on LSP excitation. Consequently, ion-induced surface nanostructuring of Ag-Au bimetallic films on amorphous silica glass and sapphire with tunable LSP excitation are presented. In addition, theoretical studies of far-field and near-field optical properties of these nanoparticles under ion irradiation are introduced, and the enhanced localized electric field (hot spot) is interpreted. Finally, the futures and challenges of the emerging plasmonic applications based on tunable LSP excitations in bio-sensing and surface enhanced Raman spectroscopy (SERS) are presented.     

Optical and morphological characterisation of a silver nanoparticle/fluorescent poly(phenylenethynylene) composite for optical biosensors

Thiol silver nanoparticles prepared by the phase transfer method have been mixed with a fluorescent poly(phenylenethynylene) sequenced with dithioester-diethylsulfide moieties in order to develop a nanocomposite for its possible application in optical biosensors for the detection and attack of fungi such as Paecilomyces variotii. Films have been prepared by dipping technique and characterized by AFM, XPS, UV-Visible and fluorescence spectroscopy. Optical Absorption properties of the nanocomposite are similar to those of the polymer with an absorption tail in the visible which supports the presence of silver nanoparticles. Despite the lack of fluorescence of the nanoparticles, the composite emits in the yellow green region and the intensity of the fluorescence of the nanocomposite film decreases after the immersion in the culture thus permitting the detection of the fungus by this technique. The fungus can be deposited on films of both the polymer and nanocomposite, nevertheless only in the latter case, an attack on mycelium is observed revealing the fungicidal effect of silver nanoparticles in the nanocomposite.     

Nanostructured surfaces and assemblies as SERS media

Metallic nanostructures attract much interest as an efficient media for surface-enhanced Raman scattering (SERS). Significant progress has been made on the synthesis of metal nanoparticles with various shapes, composition, and controlled plasmonic properties, all critical for an efficient SERS response. For practical applications, efficient strategies of assembling metal nanoparticles into organized nanostructures are paramount for the fabrication of reproducible, stable, and highly active SERS substrates. Recent progress in the synthesis of novel plasmonic nanoparticles, fabrication of highly ordered one-, two-, and three-dimensional SERS substrates, and some applications of corresponding SERS effects are discussed.     

Preparation and hydrophilicity of TiO2 sol-gel derived nanocomposite films modified with copper loaded TiO2 nanoparticles

In this study, TiO₂ nanocomposite films with 10 g/L of TiO₂ and copper loaded TiO₂ nanoparticles as nanofillers were deposited on the glass substrates using the sol gel dip-coating method. FE-SEM and UV-vis spectrophotometer were used to evaluate morphological and optical properties of copper loaded titania nanoparticles. In addition, XPS and water contact angle techniques were used to study the surface properties and superhydrophilicity of titania nanocomposite films, respectively. The results indicated that copper loaded TiO₂ nanoparticles had a significant effect on the hydrophilicity of nanocomposite film and maintaining it in a dark place for a long time (6.2 degree for titania nanocomposite films with copper loaded nanoparticle and 23.7 degree for nanocomposite film with titania nanoparticles).     

Separation by nanoparticles plasmonic resonance with low stress in microfluidics channel (analytical and design)

In this study, nanoparticles near‐field plasmonic resonance is used to improve the traditional cell separation main outputs such as viability and efficiency. The live cells viability is severely depend on stresses, which are applied on cells in the microfluidics channel. Hence, for improving the cell viability, the enforced stresses inside of the structure should be declined. The major factors of the enforced stresses are related to the electric field non‐uniformity, which are attributed to the hurdles and applied voltage magnitude. Therefore, in this study, a new structure is presented and thereby, the magnitude of the applied stresses on live cells is minimised which is contributed to the decreasing the non‐uniformity strength of channel. It should be noted that in the new structure two arrays of nanoparticles were used to produce a short range and localised non‐uniform electrical field because of their near‐field plasmonic resonance. Hence, the enforced stress on the live cell severely decreased at the far‐field and confined at the small section of the channel. It is due to, the near‐field plasmonic amplitude is dramatically disappeared by increasing distance, hence, the cells far from the nanoparticles will be endured the low level but effective amount of the optical force.Inspec keywords: nanoparticles, nanomedicine, plasmonics, cellular biophysics, microfluidics, bioMEMS, electrophoresis, separationOther keywords: optical force, dielectrophoresis, short range localised nonuniform electrical field, cell viability, microfluidics channel, cell separation, near‐field plasmonic resonance, nanoparticles