Two-dimensional Arrays Of Gold Nanoparticles Research Articles

Conformational control of two-dimensional gold nanoparticle arrays in a confined geometry within a vesicular wall

The two-dimensional (2D) assembly of gold nanoparticles (AuNPs) in a confined geometry is a rare phenomenon that has not been experimentally verified for complex systems. In this study, this process was investigated in detail using two types of block copolymers with hydrophobic and hydrophilic blocks and a series of AuNPs of three different sizes protected by hydrophobic ligands. In aqueous solutions, the selected block copolymers self-assembled into vesicular nanostructures with a hydrophobic domain in the wall, which functions as a confined geometrical space for hydrophobic AuNPs (i.e., it exerts a confinement effect and restricts the movement of AuNPs). Small-angle X-ray scattering studies revealed that AuNPs of different sizes assembled differently in the same confined geometry of the vesicular wall. In addition, optimal conditions for the formation of a regular NP array in the hydrophobic domain were determined. The AuNPs successfully self-assembled into a regular 2D lattice structure, forming a shell around the vesicle, when their size matched the thickness of the hydrophobic domain of the vesicular nanostructure. This study provides guidelines for the fabrication of nanoparticle arrays with controlled structures, which could enhance the functionality of materials and their physical properties.

Fabrication of One- and Two-Dimensional Gold Nanoparticle Arrays on Computationally Designed Self-Assembled Peptide Templates

Templating methods, combined with colloidal chemistry synthesis, provide a strategy to fabricate inorganic nanomaterials with controllable architectures. Computationally designed peptide assemblies...

Goos–Hänchen and Imbert–Fedorov shifts in a two-dimensional array of gold nanoparticles

Using an oblique linearly polarized laser beam, Goos–Hanchen (GH) and Imbert–Fedorov (IF) reflection shifts of a two-dimensional array of gold nanoparticles (NPs) on water substrate are investigated within the framework of a theoretical model. The dependences of spatial ( Δ ) and angular ( Θ ) shifts on the angle of radiation, the polarity of light, the size, and concentration of particles have been studied in detail. It is shown that a grazing p-wave light yields to the highest negative amount of GH shifts, while a 45-deg polarization that radiates at 45 deg would maximize IF shifts. The deviations are sensitive to the particle size linearly and decrease using larger NPs except in the angular out-of-plane shift ΘIF, which has a critical point where its sign and trend change. The curves of ΔGH, ΘGH, and ΘIF for various lattice constant exhibit peaks for a specific arrangement that moves toward smaller values as the particle size increases. On the other hand, ΔIF always has an additive behavior. Accurate monitoring of these parameters may serve as a precise method to determine thickness and aggregation of nanostructured films.

Guided Assembly of Two-Dimensional Arrays of Gold Nanoparticles on a Polycrystalline Gold Electrode for Electrochemical Surface-Enhanced Raman Spectroscopy

Development of a reproducible two-dimensional array of gold nanoparticles (AuNPs) through a guided assembly approach and sequentially using an electrochemical cleaning procedure to remove all cappi...

Investigating the Dynamic Behavior of TCR Microclusters by a Gold Nanoparticle Array

T cell receptor (TCR) microclusters play an important role in early signaling in T cells, and their properties and dynamic behavior are the active target of research. TCR microclusters are, however, difficult to study because their size is too small for conventional fluorescence microscopy and too large for physicochemical methods that depend on proximity effect such as FRET. We developed a new platform for probing and manipulating TCR microclusters by mechanical means. A two-dimensional array of gold nanoparticles is embedded on the glass substrate. A supported membrane, which acts as a surrogate cell membrane that has laterally fluid ligand molecules for cells, was deposited on a glass substrate with a regular array of gold nanoparticles. The supported membrane interacted with T cells and the behavior of TCR microclusters on the T cell surface was effectively altered by the gold nanoparticles. This platform offers many opportunities for studying this poorly understood size regime of protein assemblies.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Oscillatory Optical Response of an Amorphous Two-Dimensional Array of Gold Nanoparticles

The optical response of metallic nanoparticle arrays is dominated by localized surface plasmon excitations and is the sum of individual particle contributions modified by interparticle coupling that depends on specific array geometry. We demonstrate a so far unexplored distinct oscillatory behavior of the plasmon peak position, full width at half maximum, and extinction efficiency in large area amorphous arrays of Au nanodisks, which depend on the minimum particle center-to-center distance in the array. Amorphous arrays exhibit short-range order and are completely random at long distances. In our theoretical analysis we introduce a film of dipoles approach, within the framework of the coupled dipole approximation, which describes the array as an average particle surrounded by a continuum of dipoles with surface densities determined by the pair correlation function of the array.

Resonant Photoconductance of Molecular Junctions Formed in Gold Nanoparticle Arrays

We investigate the photoconductance properties of oligo(phenylene vinylene) (OPV) molecules in metal-molecule-metal junctions. The molecules are electrically contacted in a two-dimensional array of gold nanoparticles. The nanoparticles in such an array are separated by only few nanometers. This allows to bridge the distance between the nanoparticles with molecules considered as molecular wires such as OPV. We report on the photoconductance of electrically contacted OPV upon resonant optical excitation of the molecules. This resonant photoconductance is sublinear in laser intensity, which suggests that trap state dynamics of the optically excited charge carriers dominate the optoelectronic response.

Self-Assembled Two-Dimensional Array of Gold Nanoparticles with Different Size for the Sensing Application

Self-assembled two-dimensional array of gold nanoparticles (GNPs) on the glass substrate was systematically investigated in terms of glass cleaning, K2CO3 addition, GNP size, and pH of gold colloids. An ambient-air plasma treatment produced a highly-activated glass surface with the lowest air/water contact angles and K2CO3 addition is very effective to preserve the optical properties of gold nanoparticles for a long time. Small GNPs (≤40 nm) was uniformly arrayed on the amine-functionalized glass through the optimization process of electrostatic attractions between positively-charged glass and negatively-charged gold nanoparticles. For large GNPs (≥50 nm) that resulted in discrete (or loosely-packed) array on the glass substrate, pH adjustment of gold colloids (from pH 11 to 9) produced more densely-packed array of GNPs with less void areas, probably due to the reduction of electrostatic repulsion forces between large gold nanoparticles.

Surface plasmon enhanced photoconductance of gold nanoparticle arrays with incorporated alkane linkers

We report on a photoconductive gain effect in two-dimensional arrays of gold nanoparticles (NPs) in which alkane molecules are inserted. The NP arrays are formed by a self-assembly process from alkanethiol-coated gold NPs, and subsequently they are patterned on a Si/SiO2 chip by a microcontact printing technique. We find that the photoconductance of the arrays is strongly enhanced at the frequency of the surface plasmon of the NPs. We interpret the observation as a bolometric enhancement in the conductance of the NP arrays upon excitation of the surface plasmon resonance.

Diffractive coupling in gold nanoparticle arrays and the effect of disorder

Two-dimensional arrays of gold nanoparticles with a periodicity commensurate with the wavelength of resonant excitation of localized plasmons have been shown to exhibit a strong long-range interaction between particles. We investigate experimentally the effect of varying the degree of disorder in the geometrical arrangement from a periodic to a disordered lattice with constant occupancy. We also investigate the effect of disorder arising from variations in particle size for a regular lattice, and the effect this has on the broadening of the spectral line shape is discussed. A coupled dipole model is used to describe the observed spectral features.

Experimental observation of narrow surface plasmon resonances in gold nanoparticle arrays

We demonstrate that coupling between grating diffraction and localized surface plasmons in two-dimensional gold nanoparticle arrays in water leads to narrow near-infrared resonance peaks in measured far field extinction spectra. Good agreement is obtained between finite difference time domain (FDTD) calculations and experimental extinction spectra. The FDTD calculations predict that the gold nanoparticle arrays exhibit near-field electric field intensity (E2) enhancements approximately one order of magnitude greater than those of single isolated gold nanoparticles.

Spatially Controlled Functionalization and Chemical Manipulation to Fabricate Two-Dimensional Arrays of Gold Nanoparticles onto Indium Tin Oxide

We demonstrate the formation of two-dimensional (2D) arrays of gold nanoparticles (AuNPs) by controlled functionalization in a regular linear fashion, on the basis of the self-assembly and vacuum ultraviolet (VUV) lithography approaches. An octadecyltrimethoxysilane (ODS) monolayer, self-assembled on an indium tin oxide (ITO) surface, was exposed to VUV light (172 nm) through a photomask to construct the linear pattern by photodegradation of the ODS monolayer. Subsequently, an aminopropyltriethoxysilane (APS) monolayer was deposited on VUV-exposed sites by chemical vapor deposition. The immobilization of AuNPs on amino-terminated sites is due to the electrostatic attraction between citrate-stabilized AuNPs and amino groups of the APS monolayer, while the methyl-terminated sites remain unexposed. The structural organization of AuNPs in an alternating linear fashion was demonstrated by scanning electron microscope (SEM) analysis. The X-ray photoelectron microscopy (XPS) measurements were performed to probe the self-assembly of ODS, the APS monolayer, photopatterning and AuNPs immobilization.

Electron Transfer Dynamics in Two-Dimensional Arrays of Gold Nanoparticles

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Monodisperse gold nanoparticles formed on bacterial crystalline surface layers (S-layers) by electroless deposition

The fabrication of patterned arrays of nanoparticles whose electronic, optical and magnetic properties will find technological applications, such as ultra-high-density memories, is currently one of the most important objectives of inorganic material research. In this study, the in situ electroless nucleation of ordered two-dimensional arrays of gold nanoparticles (5 nm in size) by using bacterial S-layers as molecular templates and their characterization by small spot X-ray photoelectron emission spectroscopy (XPS) is presented. This yielded the elemental composition of the nanoclusters, which consisted of almost entirely elemental gold, and possible side reactions on the cluster and protein surface. The preferential deposition of the gold nanoparticles on the S-layer suggests that topography and functional groups are important for superlattice formation.

Optical excitation of coupled waveguide-particle plasmon modes: A theoretical analysis

Using the first-principles layer-multiple-scattering method we developed in previous work, we analyze recent experimental data on the extinction of light by rectangular two-dimensional arrays of gold nanoparticles on a dielectric waveguide. The theoretical results reproduce accurately the measured spectra and provide a transparent physical picture of the underlying processes.

Enhanced substrate-induced coupling in two-dimensional gold nanoparticle arrays

The influence of substrate induced coupling on plasmon excitations is probed by means of visible and near-infrared extinction microspectroscopy on various arrays of gold oblate spheroidal particles deposited onto a 20-nm-thick gold film. At zero incidence angle and for an interparticle spacing smaller than 250 nm, the spectra exhibit two bands instead of the single one observed for similar particles but deposited on indium tin oxide coated glass. We suggest that the short-wavelength band proceeds from two simultaneous mechanisms: (i) Excitation of a surface-plasmon resonance localized on the particles. (ii) Generation at the gold-glass interface of a propagating surface-plasmon wave due to the fact that the gold particles can act as a grating coupler. Surface-enhanced Raman-scattering experiments performed on oblate spheroid arrays give arguments in favor of the attribution of the long-wavelength band to surface-plasmon resonance of an ensemble of strongly coupled particles. When increasing the spacing between particles of the array beyond 250 nm, extinction spectra display the emergence of a new band. Calculations suggest that this new band proceeds from the excitation of a surface-plasmon standing wave on the film due to Bragg scattering. This assignment to Bragg scattering is supported by the investigation of the effect of varying the incidence angle under both transverse magnetic and transverse electric polarizations.

Evaporation-induced self-assembly of gold nanoparticles into a highly organized two-dimensional array

This paper provides a convenient and simple method for fabricating a self-organized two-dimensional (2D) array of gold nanoparticles on a silicon substrate. The silicon substrate, modified with an aminopropyltriethoxylsilane(APTES) monolayer, was first exposed to a gold colloidal suspension to deposit the gold particles and form a submonolayer of gold nanoparticles. This was followed by treatment with an alkanethiol solution, and then this randomly scattered submonolayer of nanosized gold particles on the silicon substrate was organized into small patches of 2D nanoparticle aggregates. Finally an alcohol solvent was used to drive these small patches of gold nanoparticle aggregates to self-organize together and form continuous ordered arrays on the silicon surface. The SEM images of the samples show that ordered two-dimensional arrays of gold nanoparticles are formed over a very large area and that the nanoparticles are highly organized and formed hexagonally closed packed structured arrays. This highly organized structure of gold nanoparticles can be reproduced over a large area by these effective procedures. Therefore, it is believed such procedures hold promise as an advanced new approach to construct ordered mesoscopic structural materials or for the controlled self-assembly of nanoparticles and could provide the possibility of detecting the collective physical properties of the ensemble.

Behaviour of two-dimensional arrays of gold nanoparticles under H 2S: agglomeration and regeneration

The use of an inorganic link, H 2S, leads to two-dimensional assemblies of the Au quantum dots via a gas phase procedure. The morphology of the networks created in this way and the behaviour of the Au nanoparticles under H 2S have been studied by scanning electron microscopy (SEM) and the absorption spectroscopy in the visible region.

Selective suppression of extinction within the plasmon resonance of gold nanoparticles

We present extinction measurements on rectangular two-dimensional arrays of gold nanoparticles on a dielectric waveguide. The spectra exhibit spectrally narrow bands of suppressed extinction within the particle–plasmon resonance, resulting from destructive interference between the incident light field and the excited waveguide modes. The dependence of the spectral position of these high-transmission bands on different waveguide modes is investigated in detail.

Nanoscale Patterns of Metal Nanoparticles Chemically-Assembled on Biomolecular Scaffolds: Assembly, Stability and Electron Transport Properties

ABSTRACTA wet chemical approach to preparing one- and two-dimensional arrays of gold nanoparticles assembled onto a polypeptide (poly-L-lysine) scaffold layer is reported. The electrical properties of biopolymer templated and nontemplated gold nanoparticle samples are compared. The electrical response of nontemplated samples is unstable, likely due to nanoparticle mobility. Biopolymer templating provides a simple, chemical method to immobilize the particles and is found to stabilize the electrical response (Coulomb blockade) of the array. A striking feature of the electrical properties is that the electron transport properties are dominated by transport through one-dimensional chains within the sample. Structural studies by AFM and XPS support the transport findings and provide evidence for the formation of one-dimensional assemblies within the arrays.