Gold Nanoparticle Arrays Research Articles

A space-tunable gold nanoparticle arrays and investigation on their SERS performance

Studies on two dimensional gold nanoparticle (2D Au NPs ) arrays evidence that intense electricmagnetic fields (‘hot spots’) generated within the gaps between adjacent Au NPs could promote the Surface-Enhanced Raman scattering (SERS) performance a lot. To achive these ‘hot spots’, tightly arrayed metallic nanostructures are required, however, fabricaton of these arrays with a facile method still poses as a challenge. In this work, a new strategy of preparing novel Au NPs arrays with UV-light tunable space between adjacent Au NPs was proposed. Photosensitive films of polyionic films containing poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl,sodium salt] (PAZO)/poly(diallyldimethyl ammonium chloride) (PDDA) on Si substrate were first prepared by implementing a Layer-by-Layer adsorption technique. Then, large-area and uniform arrays of Au NPs were tranferred onto the PAZO/PDDA films by the Langmuir-Blodgett method. SERS performance of the prepared substrate was evaluated by using 4-mercaptobenzoic acid (4-MBA) as the Raman reporter under a 785-nm laser excitation. The experimental results indicate that Raman signal can be significantly improved as the time of UV irradiating on the substrate increases. More specifically, the signal intensity at the peak of 1078 cm−1 is 1.6 times higher than that of the initial value. In consideration of the mechanism of the above observation, it is ascribed to the UV-light induced inter space shrinking between Au NPs and providing enhanced ‘hot spots’.

Electrochemical Synthesis of Flower-Like Gold Nanoparticles for SERS Application

Surface-enhanced Raman spectroscopy (SERS) is a technique that is increasingly used in the identification and quantification of organic molecules at very low concentrations. In this analytical technique SERS-active substrates play a crucial role. Beside silver, gold is also widely used as a material for making SERS substrates. In this report we present a simple method for synthesizing arrays of flower-like gold nanoparticles (also referred to as gold nanoflowers—AuNFs), which can be used as SERS substrates. The AuNFs have been electrodeposited on a silicon surface coated with silver nanoparticles, which served as seeds for the growth of AuNFs. As a result, AuNFs were formed on the silicon surface with relatively dense density and with fairly uniform distribution. Arrays of AuNFs, as SERS substrates, were tested with a rhodamine B (RhB) molecular probe. The results showed that these AuNFs allow the detection of RhB down to a concentration of 1 ppb, a relatively low concentration. This demonstrates the applicability of fabricated AuNFs as a highly active SERS substrate.

Stimuli-Responsive DNA-Linked Nanoparticle Arrays as Programmable Surfaces

Self- and directed-assembly approaches have enabled precise control over the composition and geometry of 2D and 3D nanoparticle constructs. However, the resulting structures are typically static, providing only a single structural arrangement of the nanoparticle building blocks. In this work, the power of DNA-linked nanoparticle assembly is coupled to a grayscale patterning technique to create programmable surfaces for assembly and thermally activated reorganization of gold nanoparticle arrays. Direct grayscale patterning of DNA monolayers by electron-beam lithography (DNA-EBL) enables the production of surfaces with nanometer-scale control over the density of functional DNA. This enables tuning of the particle-surface interactions with single-nanoparticle resolution and without the need for a physical template as employed in most directed assembly methods. This technique is applied on suspended membrane structures to achieve high-resolution assembly of 2D nanoparticle arrays with highly mutable architectures. Gold nanorods assembled on grayscale-patterned surfaces exhibit temperature-dependent configurations and ordering behavior that result in tunable polarization-dependent optical properties. In addition, spherical gold particles assembled from a bimodal suspension produce arrays with temperature-dependent configurations of small and large particles. These results have important implications for the design and fabrication of reconfigurable nanoparticle arrays for application as structurally tunable optical metasurfaces.

Evaluation of the inter-particle distance of gold nanoparticles dispersed on silane-treated substrates to fabricate dithiol-connected arrays

Small tunnel junctions using gold nanoparticles (GNPs) as electrodes have been studied to fabricate single-electron devices. GNPs connected via dithiol molecules have been used as small tunnel junctions, and a two-stage dispersion method was used to fabricate dithiol-connected GNP arrays. In this process, the GNPs were fixed on silane-treated substrates by immersing the substrate in a colloidal gold solution. For fabricating dithiol-connected arrays, the inter-particle distance of the dispersed GNPs must be smaller than the GNP diameter. Consequently, the inter-particle distance controlled by the immersion time (TIM1) was evaluated. For TIM1 values exceeding 8 h, the inter-particle distance was less than the GNP diameter. A second dispersion of GNPs after treating samples with dithiol realized particle connections. For the GNP arrays produced with TIM1 values greater than 8 h, the I–V characteristics were measured at 77 K, and the yield of devices exhibiting nonlinear I–V curves was 23%.

Actively Tunable Collective Localized Surface Plasmons by Responsive Hydrogel Membrane

AbstractCollective (lattice) localized surface plasmons (cLSP) with actively tunable and extremely narrow spectral characteristics are reported. They are supported by periodic arrays of gold nanoparticles attached to a stimuli‐responsive hydrogel membrane, which can on demand swell and collapse to reversibly modulate arrays period and surrounding refractive index. In addition, it features a refractive index‐symmetrical geometry that promotes the generation of cLSPs and leads to strong suppression of radiative losses, narrowing the spectral width of the resonance, and increasing of the electromagnetic field intensity. Narrowing of the cLSP spectral band down to 13 nm and its reversible shifting by up to 151 nm is observed in the near infrared part of the spectrum by varying temperature and by solvent exchange for systems with a poly(N‐isopropylacrylamide)‐based hydrogel membrane that is allowed to reversibly swell and collapse in either one or in three dimensions. The reported structures with embedded periodic gold nanoparticle arrays are particularly attractive for biosensing applications as the open hydrogel structure can be efficiently post‐modified with functional moieties, such as specific ligands, and since biomolecules can rapidly diffuse through swollen polymer networks.

Polyethylenimine-mediated gold nanoparticle arrays with tunable electric field enhancement for plasmonic applications

Localized surface plasmon resonance (LSPR) technologies are used in some of the most effective optical biosensors and can be used for the detection of biomolecules at ultralow concentrations. The construction of ordered nanoparticle arrays is important for LSPR and biosensing applications. The main challenge in the development of LSPR-based sensors is optical instability, which mainly originates from the detachment or aggregation of the gold nanoparticles (AuNPs) on the plasmonic surfaces. In this study, highly monodisperse and stable AuNPs with a particle size from 20.39 ± 1.2 to 106.17 ± 1.6 nm were synthesized by using the Turkevich and seed-and-growth methods. Here, we aimed to control the construction of plasmonic AuNPs by using the electrostatic assembly of oppositely charged polycationic polymer. For this purpose, we used positively charged polyethylenimine (PEI) to immobilize AuNPs on the disposable polystyrene surface and designed a model for plasmonic sensing. Our results confirmed that the 1-mg/mL PEI concentration efficiently prevented the aggregation or detachment of immobilized AuNPs. LSPR peak wavelengths were adjustable in the range from 530 ± 2.0 to 548 ± 1.5 nm. In addition, we theoretically showed that electric field enhancement within the gaps of nanoparticle arrays could enhance the sensitivity of the plasmonic surfaces. Such nanoplasmonic surfaces could be important in fabricating facile sensing devices and could be easily integrated into bioelectronics and microfluidic devices.

Ultra-dense (~20 Tdot/in2) nanoparticle array from an ordered supramolecular dendrimer containing a metal precursor

The fabrication of an ultra-dense, highly periodic nanoparticle array from a soft template is one of the most important issues in the fields of material science and nanotechnology. To date, block copolymer (BCP) structures have been primarily used as templates for fabricating highly periodic nanoparticle arrays with high areal densities. Herein, we demonstrate for the first time the use of a supramolecular dendrimer assembly for the formation of a highly ordered nanoparticle array with a high areal density of ~20 Tdot/in2, four times larger than that of the currently reported BCP-based nanoparticle arrays. By the simple thermal annealing of a dendrimers containing a metal precursor between two flat, solid substrates, a hexagonal array of small gold nanoparticles (with a diameter of ~1.6 nm and center-to-center distance of ~5.3 nm), oriented normal to the bottom, was achieved. Density functional theory calculations demonstrated that the gold cation strongly bound to the head group of the dendrimer. This structure served as a building block for self-assembly into a stable cylindrical structure. We anticipate that this study will lead to the creation of a large family of supramolecular dendrimers that can be utilized as soft templates for creating periodic, ultra-dense nanoparticle arrays.

Design of a Dual-Technology Fusion Sensor Chip with a Ring Electrode for Biosensing Application.

Quartz crystal microbalance (QCM) is still a new high-precision surface detection technique. However, the adsorption quality detected by the QCM currently contains a solvent-coupling quality and cannot separate the actual biomolecular mass. Local surface plasmon resonance (LSPR) can detect the mass of biomolecules, but requires a certain contrast between the solvent of the surrounding medium and the refractive index of the adsorbed layer. The sensor chip, combining two compatible technologies, can realize the simultaneous detection of biomolecules and improve the refractive index sensitivity. The structure of our chip is to prepare the ring-shaped gold electrode on the upper surface of the quartz crystal, the circular gold electrode on the bottom surface, and the spherical gold nanoparticles arrays in the center region of the ring electrode to form a QCM/LSPR dual-technology chip. Through simulation, we finally get the size of the best energy trap by the two electrodes on the upper surface and the lower surface: the ring-top electrode with a thickness of 100 nm, an inner diameter of 4 mm, and an outer diameter of 8 mm; and the bottom electrode with a thickness of 100 nm and a radius of 6 mm. By comparing the refractive index sensitivity, we chose a spherical gold nanoparticle with a radius of 30 nm and a refractive sensitivity of 61.34 nm/RIU to design the LSPR sensor chip.

Ultrasonication‐Induced Self‐Assembled Fixed Nanogap Arrays of Monomeric Plasmonic Nanoparticles inside Nanopores

AbstractMonomeric gold (Au) and silver (Ag) nanoparticle (NP) arrays are self‐assembled uniformly into anodized aluminium oxide (AAO) nanopores with a high homogeneity of greater than 95%, using ultrasonication. The monomeric metal NP array exhibits asymmetric plasmonic absorption due to Fano‐like resonance as interpreted by finite‐difference time‐domain (FDTD) simulation for the numbers up to 127 AuNPs. To examine gap distance‐dependent collective‐plasmonic resonance, the different dimensions of S, M, and L arrays of the AuNP diameters/the gap distances of ≈36 nm/≈66 nm, ≈45 nm/≈56 nm, and ≈77 nm/≈12 nm, respectively, are prepared. Metal NP arrays with an invariable nanogap of ≈50 nm can provide consistent surface‐enhanced Raman scattering (SERS) intensities for Rhodamine 6G (Rh6G) with a relative standard deviation (RSD) of 3.8–5.4%. Monomeric arrays can provide an effective platform for 2D hot‐electron excitation, as evidenced by the SERS peak‐changes of 4‐nitrobenzenethiol (4‐NBT) adsorbed on AgNP arrays with a power density of ≈0.25 mW µm‐2 at 514 and 633 nm. For practical purposes, the bacteria captured by 4‐mercaptophenylboronic acid are found to be easily destroyed under visible laser excitation at 514 nm with a power density of ≈14 mW µm‐2 for 60 min using Ag due to efficient plasmonic‐electron transfer.

Polymer-Templated Gold Nanoparticles on Optical Fibers for Enhanced-Sensitivity Localized Surface Plasmon Resonance Biosensors.

Dense arrays of well-dispersed gold nanoparticles (AuNPs) on optical fibers are shown to bridge the gap in sensitivity and sensing performance between localized surface plasmon resonance (LSPR) and classical SPR sensing. A simple self-assembly method relying on a poly(styrene- b-4-vinylpyridine) (PS- b-P4VP) block copolymer brush layer was used to immobilize AuNPs of different diameters from 10 to 92 nm on optical fibers. In comparison with standard AuNP deposition methods using (3-aminopropyl)trimethoxysilane (APTMS) and polyelectrolytes, the sensitivity with the PS- b-P4VP templating method was found to be 3-fold better, a consequence of the smaller gap between particles and the presence of fewer AuNP aggregates. Hence, the sensitivity of the LSPR sensor for IgG was comparable to a classical SPR, also on optical fibers, and about 68% of that for a prism-based wavelength-interrogation SPR instrument. The reproducibility and the detection limit of the LSPR sensor were about the same as the SPR sensor. The enhanced performance of the LSPR sensors using the PS- b-P4VP block copolymer fabrication method paves the way for use of these LSPR biosensors in a smaller and more cost-effective platform.

Limits of the Effective Medium Theory in Particle Amplified Surface Plasmon Resonance Spectroscopy Biosensors

The resonant wave modes in monomodal and multimodal planar Surface Plasmon Resonance (SPR) sensors and their response to a bidimensional array of gold nanoparticles (AuNPs) are analyzed both theoretically and experimentally, to investigate the parameters that rule the correct nanoparticle counting in the emerging metal nanoparticle-amplified surface plasmon resonance (PA-SPR) spectroscopy. With numerical simulations based on the Finite Element Method (FEM), we evaluate the error performed in the determination of the surface density of nanoparticles σ when the Maxwell-Garnett effective medium theory is used for fast data processing of the SPR reflectivity curves upon nanoparticle detection. The deviation increases directly with the manifestations of non-negligible scattering cross-section of the single nanoparticle, dipole-dipole interactions between adjacent AuNPs and dipolar interactions with the metal substrate. Near field simulations show clearly the set-up of dipolar interactions when the dielectric thickness is smaller than 10 nm and confirm that the anomalous dispersion usually observed experimentally is due to the failure of the effective medium theories. Using citrate stabilized AuNPs with a nominal diameter of about 15 nm, we demonstrate experimentally that Dielectric Loaded Waveguides (DLWGs) can be used as accurate nanocounters in the range of surface density between 20 and 200 NP/µm2, opening the way to the use of PA-SPR spectroscopy on systems mimicking the physiological cell membranes on SiO2 supports.

Nanostructured Bifunctional Hydrogels as Potential Instructing Platform for Hematopoietic Stem Cell Differentiation

Hematopoietic stem cells (HSCs) are blood forming cells which possess the ability to differentiate into all types of blood cells. T cells are one important cell type HSCs can differentiate into, via corresponding progenitor cells. T cells are part of the adaptive immune system as they mediate cellular immune responses. Due to this crucial function, in vitro differentiated T cells are subject of current studies in the biomedical field in terms of cell transplantation. Studies show that the density of the immobilized Notch ligand Delta-like 1 (DLL1) presented in HSCs´ environment can stimulate their differentiation toward T cells. The development of reliable synthetic cell culture systems presenting variable densities of DLL1 is promising for the future expansion of T cells´ clinical applications. Here we introduce bifunctional polyethylene glycol-based (PEG-based) hydrogels as potential instructing platform for the differentiation of human hematopoietic stem and progenitor cells (HSPCs) to T cells. PEG hydrogels bearing the cell adhesion supporting motif RGD (arginyl-glycyl-aspartic acid) were synthesized by UV-light induced radical copolymerization of PEG diacrylate and RGD modified PEG acrylate. The hydrogels were furthermore nanostructured by incorporation of gold nanoparticle arrays that were produced by block copolymer micelle nanolithography (BCML). BCML allows for the decoration of surfaces with gold nanoparticles in a hexagonal manner with well-defined interparticle distances. To determine the impact of DLL1 density on the cell differentiation, hydrogels with particle distances of approximately 40 nm and 90 nm were synthesized and the gold nanoparticles were functionalized with DLL1. After 27 days in culture, HSPCs showed an unphysiological differentiation status and, therefore, the differentiation was evaluated as atypical T lymphoid differentiation. Cluster of differentiation (CD) 4 was the only tested T cell marker which was expressed clearly in all samples. Thus, although the applied nanopatterned hydrogels affected two important signaling pathways (integrins and Notch) for T cell differentiation, it appears that more functionalities that control T cell differentiation in nature need to be considered for achieving fully synthetic in vitro T cell differentiation strategies.

Plasmonic Nanosensor Array for Multiplexed DNA-based Pathogen Detection.

In this research we introduce a plasmonic nanoparticle based optical biosensor for monitoring of molecular binding events. The sensor utilizes spotted gold nanoparticle arrays as sensing platform. The nanoparticle spots are functionalized with capture DNA sequences complementary to the analyte (target) DNA. Upon incubation with the target sequence, it will bind on the respectively complementary functionalized particle spot. This binding changes the local refractive index, which is detected spectroscopically as the resulting changes of the localized surface plasmon resonance (LSPR) peak wavelength. In order to increase the signal, a small gold nanoparticle label is introduced. The binding can be reversed using chemical means (10 mM HCl). It is demonstrated that multiplexed detection and identification of several fungal pathogen DNA sequences subsequently on one sensor array are possible by this approach.

Self-Healing Plasmonic Metal Liquid as a Quantitative Surface-Enhanced Raman Scattering Analyzer in Two-Liquid-Phase Systems.

Liquid-state interfacial plasmonic systems are emerging as an alternative for the quantitation and practicability of the surface-enhanced Raman scattering (SERS) technique in analytical science, especially for complex liquid-phase systems. Here we show a general strategy for the three-dimensional (3D) self-assembly of gold nanoparticle (GNP) arrays on a spherical oil-water (O-W) interface, denoted as a plasmonic metal liquid (PML). The PML has excellent self-healing and shape-adaptive features; it can be transferred into containers of any shape; and it presents fast, quantitative, and multiplex SERS capability. Accurate control of nanoparticle density (PD) on the 3D interface enables tunable SERS strength. In situ synchrotron radiation small angle X-ray scattering (SR-SAXS) provides evidence that the interfacial PD is quantifiable and can be precisely regulated in the range of 24-216 particles/μm2, which produces optimizable Raman enhancement. The strongest SERS signal is achieved at 167 particles/μm2 with GNP diameters of approximately 64 nm. In particular, the O phase acts not only as the assembly media for spherical PML arrays but also as the extracting agent for targets with different natures in complex media. Moreover, the O phase with continuous-phase features generates inherent and sharp SERS fingerprints and provides an effective internal standard (IS) for calibrating the fluctuation of samples and measuring conditions. By virtue of the triple roles of the O phase, the PML platform exhibits excellent mechanical stability, detection sensitivity, and signal reproducibility. This study demonstrates the concept of a fast and quantitative liquid-state SERS platform in common cuvettes on a portable Raman device that is as simple as a spectrophotometer.

Optical Conduction Resonance in Self-Assembled Metal Nanoparticle Array-Dielectric Thin Films

Optical conduction resonance- (OCR-) enhanced third-order optical nonlinearity of two dimensional (2D) periodic gold nanoparticle array-dielectric thin films has been investigated. The third-order optical susceptibility of periodic gold nanoparticle array embedded in silica thin film shows ~104 enhancement comparing to gold nanoparticle colloids. The 2D gold nanoparticle arrays were synthesized by using the electrostatic self-assembly (ESA) technique. During the fabrication process, the positively or negatively functionalized gold nanoparticles are automatically self-aligned to establish a 2D array with a very small interparticle spacing due to the polymer shell on the metal particles. Then, a monolayer of silica can be coated on the top of the 2D metal nanoparticle array. This type of 2D gold nanoparticle array-dielectric thin films has high volume fraction of gold nanoparticles. According to the extended Maxwell-Garnett theory, this kind of films can exhibit OCR. The OCR frequency can be tuned from visible to mid-infrared by controlling the gold nanoparticle volume fraction. During OCR, the real part of the composite dielectric constant is zero to make the induced electromagnetic waves in gold nanoparticles to couple effectively within the film. The open-aperture z-scan technique is used to measure the nonlinear optical properties of the ESA films.

Superficial-Layer-Enhanced Raman Scattering (SLERS) for Depth Detection of Noncontact Molecules.

Although the strength of Raman signals can be increased by many orders of magnitude on noble metal nanoparticles, this enhancement is confined to an extremely short distance from the Raman-active surface. The key to the development of Raman spectroscopy for applications in diagnosis and detection of cancer and inflammatory diseases, and in pharmacology, relies on the capability of detecting analytes that are noninteractive with Raman-active surfaces. Here, a new Raman enhancement system is constructed, superficial-layer-enhanced Raman scattering (SLERS), by covering elongated tetrahexahedral gold nanoparticle arrays with a superficial perovskite (CH3 NH3 PbBr3 ) film. Plasmonic decay is depressed along the vertical direction away from the noble metal surface and the penetration depth is increased in the perovskite media. The vertical penetration of SLERS is verified by the spatial distribution of the analytes via Raman imaging in layer-scanning mode.

Sensitive and Reproducible Gold SERS Sensor Based on Interference Lithography and Electrophoretic Deposition.

Surface-enhanced Raman spectroscopy (SERS) is a promising analytical tool due to its label-free detection ability and superior sensitivity, which enable the detection of single molecules. Since its sensitivity is highly dependent on localized surface plasmon resonance, various methods have been applied for electric field-enhanced metal nanostructures. Despite the intensive research on practical applications of SERS, fabricating a sensitive and reproducible SERS sensor using a simple and low-cost process remains a challenge. Here, we report a simple strategy to produce a large-scale gold nanoparticle array based on laser interference lithography and the electrophoretic deposition of gold nanoparticles, generated through a pulsed laser ablation in liquid process. The fabricated gold nanoparticle array produced a sensitive, reproducible SERS signal, which allowed Rhodamine 6G to be detected at a concentration as low as 10−8 M, with an enhancement factor of 1.25 × 105. This advantageous fabrication strategy is expected to enable practical SERS applications.

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...

Significant enhancement of direct electric communication across enzyme-electrode interface via nano-patterning of synthetic glucose dehydrogenase on spatially tunable gold nanoparticle (AuNP)-modified electrode

In this study, the effect of inter-enzyme steric hindrance that occurs during enzyme immobilization on the electrode, on direct electrical communications of enzyme with electrode was investigated via nano-patterning of enzymes on the electrode. Here, the nano-patterning of enzymes was achieved through the combination of DET-capable enzyme that was produced via fusion of site-specific gold binding peptide (GBP) to catalytic subunit of enzyme and gold nanoparticle (AuNP) array with highly tunable dimensions of AuNPs, resulting in spatially controllable enzyme-electrode. The nano-scale spatial control between immobilized enzymes on the highly tuned AuNPs shows different DET efficiency across the enzyme-electrode interface, showing 18.47% of maximum electron recovery which is 3.2-fold enhanced electron recovery efficiency compared to spatially non-controlled enzymes on the electrode where showed 5.7% of electron recovery. The result affirms that inter-enzyme interaction is a significant parameter that decides the enzyme-electrode performance.

An optoelectronic tongue based on an array of gold and silver nanoparticles for analysis of natural, synthetic and biological antioxidants

A colorimetric array, which can discriminate 20 food antioxidants of natural, synthetic and biological groups, is described. It consists of gold and silver nanoparticles that were synthesized using six different reducing and/or capping agents. The function of the array relies on the interaction of the antioxidants with the nanoparticles which causes aggregation or morphological changes. This, in turn, causes a change in the sensors' colors. The array produces a unique combination of colors for each antioxidant. The resulting colorations are determined by recording the absorbances of the arrays at wavelengths of 405, 450, 490 and 630 nm, or by capturing the images with a digital camera. The discriminatory ability of the array is investigated by principle component analysis and hierarchical cluster analysis. The method was applied to quantitative assay of gallic acid, caffeic acid, catechin, dopamine, citric acid, butylated hydroxytoluene and ascorbic acid. The respective limits of detection are 4.2, 13, 53, 6.9, 47, 3.5 and 43nM, respectively. The simultaneous determination of 5 different antioxidants is achieved utilizing partial least square regression. The root mean square errors for prediction of the test set are 0.0650, 0.0782, 0.811, 0.0206 and 0.135nM for gallic acid, catechin, butylated hydroxytoluene, dopamine, and ascorbic acid, respectively. This method demonstrates excellent potential for analysis of antioxidants in beverages such as tea and lemon juice. Graphical abstract Schematic of a method for the simultaneous determination of several antioxidants based on changes in the color of gold and silver nanoparticles. The antioxidants cause aggregation and/or morphological changes which can be detected by using both image analysis or by colorimetry.