Arrangement Of Gold Nanoparticles Research Articles

Sensitivity enhancement of the LSPR-based tapered optical fiber biosensor by variation of nanoparticle arrangement

A tapered optical fiber sensor with four arrangements of gold nanoparticles (Au NPs) on its waist is simulated and the fiber transmittance by changing the analyte refractive index (RI) is obtained. The method is a combination of the finite-difference time-domain method and the finite element method. The effect of NPs on top of each other and dimers is investigated, which is the first step in studying the aggregation of NPs in the cluster NP model. In addition, the effects of fiber diameter, NP diameter, and fiber length are examined. It is shown that by variation of NP arrangement, the amplitude sensitivity increases from 1.5 per refractive index unit (RIU−1) to 4.53RIU−1 and the wavelength sensitivity increases from 58.24 to 116.74 nm/RIU. The dimensions of the structures and the ranges of analyte RIs are in the field of practical biosensors, to be close to reality and to be effective in diagnosing diseases.

Towards Digital Twins of Plasmonic Sensors: Constructing the Complex Numerical Model of a Plasmonic Sensor Based on Hexagonally Arranged Gold Nanoparticles.

In this work, we aim to design the digital twin of a plasmonic sensor based on hexagonally arranged ellipsoidal gold nanoparticles fixed to a glass substrate. Based on electron microscopy images of three experimentally realized nanoparticle arrangement types, we constructed numerical models in environments based on finite element method (FEM) and boundary element method (BEM), namely COMSOL Multiphysics for FEM and the MNPBEM Matlab Toolbox for BEM. Models with nonperiodic and periodic boundary conditions with different unit cells were constructed to study the plasmonic behavior of both the single ellipsoidal particles and the hexagonal nanoparticle arrangements. The effect of the geometrical parameters, namely the interparticle distance, the nanoparticle diameter and thickness, on the resulting LSPR peak positions and bulk refractive index sensitivities were studied in detail, also taking into account the effect of the SiO2 substrate (pillars) under the ellipsoidal particles. We have demonstrated that by optimizing the models, the LSPR peak positions (and sensitivities) can match the experimentally measured values within 1 nm (nm/RIU) precision. The comparison of simulation conditions and the detailed discussion of the effect of the geometrical parameters and used gold dielectric functions on the obtained sensitivities can be very beneficial for the optimization of plasmonic sensor constructions through numerical simulations.

A highly sensitive electrochemical sensor derived from peptide amphiphilic inspired self-assembled, ordered gold nanoparticles for determination of 22 β-lactams

Achieving ordered arrangement of gold nanoparticles (AuNPs) on an electrode can further improve the signal intensity of an electrochemical immunosensor. This ordered AuNPs self-assembly can be inspired by peptide amphiphile (PA). The rational design of hydrophobic chains in PA is a crucial step when the range of hydrophobic alkane chain from 14 to 18 carbons. As arginine (R) can combine specifically with Au surface plane (111), four PAs, i.e., C15H23CO-RR (C16R2), C15H23CO-RRR (C16R3), C15H23CO-RRRR (C16R4), and C15H23CO-RRRRR (C16R5), in this work are designed to investigate the extent of ordered AuNPs self-assembly. The results indicate that C16R4 presented a dominant electron donating ability and can inspire the self-assembly of AuNPs to form a mono-dispersed raspberry-like structure (C16R4-AuNPs) to obtain the largest ΔI (15.4 μA). In the detection system, C16R4-AuNPs firstly capture and immobilize anti-β-lactam receptor monoclonal antibodies (mAb) by electrostatic adsorption, and the anti-β-lactam receptor mAb possess antigen-antibody binding sites away from the active site of the receptors. Then, they capture β-lactam receptors through an antigen-antibody reaction to form a ternary complex (C16R4-AuNPs-mAb-β-lactam receptors). Based on this indirect-labeling process, the receptor active sites have been exposed completely, facilitating ligand recognition, which greatly further improves the sensitivity of the present method. Finally, a highly sensitive electrochemical immunosensor based on the ternary complex is developed to achieve the determination of 22 β-lactam antibiotics, which is more sensitive and applicable than other reported electrochemical sensors.

1D micro-nanopatterned integrin ligand surfaces for directed cell movement.

Cell-extracellular matrix (ECM) adhesion mediated by integrins is a highly regulated process involved in many vital cellular functions such as motility, proliferation and survival. However, the influence of lateral integrin clustering in the coordination of cell front and rear dynamics during cell migration remains unresolved. For this purpose, we describe a novel protocol to fabricate 1D micro-nanopatterned stripes by integrating the block copolymer micelle nanolithography (BCMNL) technique and maskless near UV lithography-based photopatterning. The photopatterned 10μm-wide stripes consist of a quasi-perfect hexagonal arrangement of gold nanoparticles, decorated with the RGD (arginine-glycine-aspartate) motif for single integrin heterodimer binding, and placed at a distance of 50, 80, and 100nm to regulate integrin clustering and focal adhesion dynamics. By employing time-lapse microscopy and immunostaining, we show that the displacement and speed of fibroblasts changes according to the nanoscale spacing of adhesion sites. We found that as the lateral spacing of adhesive peptides increased, fibroblast morphology was more elongated. This was accompanied by a decreased formation of mature focal adhesions and stress fibers, which increased cell displacement and speed. These results provide new insights into the migratory behavior of fibroblasts in 1D environments and our protocol offers a new platform to design and manufacture confined environments in 1D for integrin-mediated cell adhesion.

Synthesis and Organization of Gold-Peptide Nanoparticles for Catalytic Activities.

A significant development in the synthesis strategies of metal-peptide composites and their applications in biomedical and bio-catalysis has been reported. However, the random aggregation of gold nanoparticles provides the opportunity to find alternative fabrication strategies of gold-peptide composite nanomaterials. In this study, we used a facile strategy to synthesize the gold nanoparticles via a green and simple approach where they show self-alignment on the assembled nanofibers of ultrashort oligopeptides as a composite material. A photochemical reduction method is used, which does not require any external chemical reagents for the reduction of gold ions, and resultantly makes the gold nanoparticles of size ca. 5 nm under mild UV light exposure. The specific arrangement of gold nanoparticles on the peptide nanofibers may indicate the electrostatic interactions of two components and the interactions with the amino group of the peptide building block. Furthermore, the gold-peptide nanoparticle composites show the ability as a catalyst to degradation of environmental pollutant p-nitrophenol to p-aminophenol, and the reaction rate constant for catalysis is calculated as 0.057 min–1 at a 50-fold dilute sample of 2 mg/mL and 0.72 mM gold concentration in the composites. This colloidal strategy would help researchers to fabricate the metalized bioorganic composites for various biomedical and bio-catalysis applications.

AuNPs network structures as a plasmonic matrix for ultrasensitive immunoassay based on surface plasmon resonance spectroscopy

Nanoparticle gap, degree of order, and the structure of the nanocomposite functionalized interface have a significant impact on sensing properties. Orderly arranged gold nanoparticles enhance the local surface plasmon resonance and the surface plasmon wave coupling on the surface of the gold film, thereby effectively improving the SPR sensitivity. The orderly adjustment of AuNPs spacing can be achieved by changing the concentration of guest, and a precise self-assembled three-dimensional network structure (3D NS) can be successfully constructed. A simple and feasible sensor based on the 3D NS formed by the self-assembly of pSC4-AuNPs was proposed. SPR refractive index change experiment was performed to value the sensitivity performance of the sensor, and the three main parameters were improved. Multiple optimization experiments proved that 3D NS mediated by 1 mM paraquat showed the highest SPR sensitization effect. Bovine serum albumin antibody immune experiment was performed as a model to verify the SPR performance of 3D NS, which was identical to the performance analysis experiment.

Hierarchical superstructures assembled from pH-responsive gold nanoparticles in deformable emulsion droplets.

Integrating stimuli-responsive nanoparticles (NPs) into shape-tunable hierarchical superstructures has emerged as a powerful way to fabricate smart materials. Here, we propose a robust strategy for the fabrication of sheet-like superlattices and hollow capsules by precisely tuning the interfacial tension of emulsion droplets containing pH-responsive gold nanoparticle building blocks, providing an efficient route to construct hierarchical superstructures with different applications.

Controlled Arrangement of Gold Nanoparticles on Planar Surfaces via Constrained Dewetting of Surface-Grafted RAFT Polymer.

Linear and four-arm star polystyrene samples prepared by RAFT polymerization were grafted to gold surfaces directly via their thiocarbonylthio-end groups. Nanoscale polymer patterns were subsequently formed via constrained dewetting. The patterned polymer films then served as a template for the precise arrangement of gold nanoparticles in a monolayer with a well-defined and regular structure. Using star polymers as a linker between the planar gold surface and the particles, the structural stability of the arranged particles can be further enhanced. The surface-bound nanocomposite films made of polymer and nanoparticles can also reversibly switch their nanostructures by simple wetting or dewetting treatment.

Third order nonlinear optical properties of gold/alumina multilayer nanocomposites with different nanoparticle arrangements

The linear and nonlinear optical properties of gold nanoparticle/alumina matrix multilayer nanocomposites obtained by successive laser deposition were studied. The nonlinear optical properties of the gold nanoparticle layers embedded in alumina were determined by Z-scan at 532 nm, using a picosecond pulse laser. The linear absorption, third-order nonlinear absorption and refraction were found to depend on the arrangement of gold nanoparticles in the nanocomposite thin film, when essential characteristics such as nanoparticle dimension, metal concentration and total film thickness are constant. When partial self-correlation between gold nanoparticles in successive layers occurs, in the case of thin alumina layers, linear and nonlinear optical properties of the nanocomposites are enhanced, reaching values of -2.8 × 10−6 m/W and 1.6 × 10−13 m2/W for the third-order nonlinear absorption and refraction coefficients, respectively.

Mesoporous silica supported orderly-spaced gold nanoparticles SERS-based sensor for pesticides detection in food

In this study, a novel sensor fabricated with compactly arranged gold nanoparticles (AuNPs) templated from mesoporous silica film (MSF) via air-water interface has been confirmed as a promising surface-enhanced Raman scattering (SERS) substrate for detecting trace levels of 2,4-dichlorophenoxyacetic acid (2,4-D), pymetrozine and thiamethoxam. The densely arranged AuNPs@MSF had an average AuNPs size of 5.15 nm with small nanogaps (<2nm) between AuNPs, and exhibited a high SERS performance. SERS spectra of pesticides were collected after their adsorption on the AuNPs@MSF. The results showed that the concentration of 2,4-D, pymetrozine and thiamethoxam gave a good linear relationship with SERS intensity. Moreover, the designed SERS-based sensor (AuNPs@MSF) was stable for 3 months with ca. 3% relative standard deviation (RSD) and was applied successfully for the analysis of 2,4-D extraction from both environmental and food samples. The proposed SERS-based sensor was further validated by HPLC and showed satisfactory result (p > 0.05).

Tensile control of the thermal flow in plasmonic heaters realized on flexible substrates.

In this paper, we present a simple and robust numerical method capable of predicting, with high accuracy, the thermal effects occurring for different gold nanoparticle arrangements under externally applied strain. The physical system is numerically implemented in the COMSOL Multiphysics simulation platform. The photothermal response of different arrangements of gold nanoparticles, resonantly excited by linearly polarized light, is considered with the system at rest and under the action of mechanical stress. The generation of heat at the nanoscale is analyzed by considering how this is affected by the variation of the extinction cross section. We describe the peculiar conditions under which mechanically controlled gold nanoparticle arrangements can significantly increase the local temperature due to the formation of localized photothermal hot spots. The resulting systems are envisioned in applications as optomechanically tunable plasmonic heaters.

Uniform arrangement of gold nanoparticles on magnetic core particles with a metal-organic framework shell as a substrate for sensitive and reproducible SERS based assays: Application to thequantitation of Malachite Green and thiram.

Magnetite (Fe3O4) spheres acting as a core were evenly decorated with gold nanoparticles (AuNPs) and coated with a shell of a metal organic framework (MOF) of type MIL-100(Fe). The resulting hybrid nanomaterial of type Fe3O4-Au@MIL-100(Fe) hybrid is shown to be a viable new SERS substrate. The integration of magnetic core, build-in plasmonic gold nanoparticles and a MOF shell endows the Fe3O4-Au@MIL-100(Fe) with highly efficient magnetic separation and enrichment ability, abundant interparticle hotspots, and significant chemical enhancement effect. This leads to a large enhancement, and greatly improved reproducibility of the SERS signals as shown for Malachite Green (MG) and the fungicide thiram. MG in solution can be quantified with a 50-fold lower detection limit (0.14nM for peak at 1398cm-1) and largely improved reproducibility (RSD = 9%, 1398cm-1) when compared to the use of (a) AuNPs anchored on MIL-100(Fe) (RSD = 27%, 1186cm-1), or (b) AuNPs embedded in MIL-100(Fe) (RSD = 36%, 1398cm-1). The method was applied to the quantitation of MG and thiram in spiked water samples. The lower limits of detection are 4.4nM for MG (1398cm-1) and 15nM for thiram (1380cm-1), respectively, and signals' RSDs are 13% (1398cm-1) and 5% (1380cm-1) for MG and thiram, respectively. The substrate is recyclable. Graphical abstract Schematic illustration of the preparation and SERS molecule sensing application of Fe3O4-Au@MIL-100(Fe) hybrid. PMMA: poly(methacrylic acid; BPEI: branched poly(ethyleneimine); BTC: 1,3,5-tricarboxybenzene.

Smart Golden Leaves Fabricated by Integrating Au Nanoparticles and Cellulose Nanofibers

AbstractA simple processing technology based on spontaneous arrangement of gold nanoparticles (AuNPs) on cellulose nanofibers (CNFs) makes it possible to form a gold leaf with superior mechanical, chemical and electrical characteristics with a small amount of gold (&lt;15 vol.%). The electrical resistivity of the AuNP/CNF hybrid film reached 8.7×10−6 Ω cm at 13 vol.% corresponding to that of a gold plate (2.9×10−6 Ω cm) through a distribution of AuNP inside the film in the form of a band. The AuNPs work not only as linkers between various CNFs in the hybrid structure but also as scaffolds. Self‐assembly allows the formation of leaves on three‐dimensional micrometer‐sized substrates, on which it is impossible to form a uniform flexible metallic layer using conventional techniques such as sputtering, vapor deposition, and electroless plating. The hybrid film holds great promise as a novel gold leaf for a wide range of applications, including coatings, smart papers, electronic skins, and wearable devices owing to its unique combination of superior properties, as well as good productivity, processability, and renewability.

3D confined assembly of polymer-tethered gold nanoparticles into size-segregated structures

A mixture of binary polystyrene (PS)-tethered gold nanoparticles (GNPs) with different sizes can co-assemble into size-segregated core–shell structures under 3D confinement. The location and arrangement of GNPs can be effectively tuned by varying the chain length of the modified PS.

Functionalized gold electroless-plated optical fiber gratings for reliable surface biosensing

In the context of plasmonic sensing using optical fibers, the controlled deposition of thin metal films remains a challenge, especially because of their cylindrical shape. In this work, we study the gold electroless plating (ELP), which is a direct and cost-effective technique to improve the quality and reproducibility of the metal deposition. In this paper, we use optical fibers to monitor the deposition process in real time. Our analysis is conducted on gratings photo-imprinted in the fiber core. Using polarized light, we show how the comb-like amplitude spectra of tilted fiber Bragg gratings (TFBGs) evolve depending on the ELP duration. This spectral evolution linked to a thorough study of the metal surface allows us to define the optimized process for improved surface refractometry. We experimentally show that this happens for a particular arrangement of gold nanoparticles yielding spectral features comparable to those obtained for localized surface plasmon resonance (LSPR) excitation. Biosensing experiments were performed and a LOD of 1 ng/mL (14 pM) is reported. This comes along with an enhanced specificity, contrasting with a poor sensitivity to bulk refractive index. All this is paving the way to a fast online coating procedure for nano-scaled and label-free biosensing using optical fibers.

Site Selective Arrangement of Gold Nanoparticles on Aminosilane Self-Assembled Monolayer Modified Indium Tin Oxide

Site Selective Arrangement of Gold Nanoparticles on Aminosilane Self-Assembled Monolayer Modified Indium Tin Oxide

Radiative Pumping and Propagation of Plexcitons in Diffractive Plasmonic Crystals.

Strong coupling between plasmons and excitons leads to the formation of plexcitons: quasiparticles that combine nanoscale energy confinement and pronounced optical nonlinearities. In addition to these localized modes, the enhanced control over the dispersion relation of propagating plexcitons may enable coherent and collective coupling of distant emitters. Here, we experimentally demonstrate strong coupling between carbon nanotube excitons and spatially extended plasmonic modes formed via diffractive coupling of periodically arranged gold nanoparticles (nanodisks, nanorods). Depending on the light-matter composition, the rather long-lived plexcitons (>100 fs) undergo highly directional propagation over 20 μm. Near-field energy distributions calculated with the finite-difference time-domain method fully corroborate our experimental results. The previously demonstrated compatibility of this plexcitonic system with electrical excitation opens the path to the realization of a variety of ultrafast active plasmonic devices, cavity-assisted energy transport and low-power optoelectronic components.

High surface roughness gold nanoparticle/centimeter level silver nanowire heterostructure detectors for SERS application

Gold nanoparticle/centimeter level silver nanowire heterostructures were prepared by vacuum thermal evaporation method and solid-state ionics method under 10 μA direct current electric field (DCEF) using fast ionic conductor RbAg4I5 films. The surface morphology and chemical composition of the heterostructures were characterized by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), respectively. The surface enhanced Raman scattering (SERS) performance was detected by Rhodamine 6 G (R6 G) aqueous solutions as probe molecules. The results indicate that the gold nanoparticle/silver nanowire heterostructures were long-range order and short-range order with the longest length of 2 cm were prepared by vacuum thermal evaporation method and solid-state ionics method. The diameters of the heterostructures ranged from 40 to 90 nm and many regularly arranged gold nanoparticles with the diameter from 5 to 20 nm lie in the prepared heterostructures, which lead to the heterostructures have high surface roughness. The molar ratio of Au:Ag in the heterostructures is 1:19. The limiting concentrations of R6 G for the prepared high surface roughness gold nanoparticle/silver nanowire heterostructures SERS substrates is 10−17 mol/L.

Bimetallic Network with Hetero‐interfacial Plasmons

AbstractFabrication of bimetallic networks consisting of periodically arranged gold nanoparticles (AuNPs) embedded with a grid of silver nanowires, where solution‐processing materials or techniques are involved in all of the fabrication procedures, is reported. Annealing of the colloidal gold nanoparticles and the photoreduction of the silver ions in the mixture solution of AgNO3 and polyvinyl pyrrolidone in water are the main processes. The key to this fabrication is that the AuNP array is used as the mask for the photoreduction of silver ions into nanowires, where the silver nanowires are thus located between the AuNPs. Two sets of dipolar and quadrupolar plasmons, as well as their respectively coupled resonance modes, are observed in the measurements and specified using theoretical analysis. Thus, the bimetallic photonic structures not only show enhanced and extended resonance spectrum due to the overlap of multiple localized surface plasmons but also induce plasmonic hetero‐interfacial interaction between the closely adjacent AuNPs and silver nanowires.

Chiral DNA Origami Nanotubes with Well-Defined and Addressable Inside and Outside Surfaces.

We report the design and assembly of chiral DNA nanotubes with well-defined and addressable inside and outside surfaces. We demonstrate that the outside surface can be functionalised with a chiral arrangement of gold nanoparticles to create a plasmonic device and that the inside surface can be functionalised with a track for a molecular motor allowing transport of a cargo within the central cavity.