Gold Arrays Research Articles

Optical Effects in Magnetic Hyperbolic Metamaterials

Abstract—We present the results of synthesis of arrays of gold and bilayer Au/Ni nanorods in a matrix of porous anodic alumina and of experimental investigation and numerical simulation of their optical and magnetooptical properties. We show that the spectra of these structures have two singular features located near 520 nm and in the range of 700–800 nm. Au/Ni nanorods exhibit a significant modulation and enhancement of the magnetooptical intensity effect in the range of the long-wavelength resonance. Experimentally observed features agree with results of numerical simulation.

Plasmon coupling between complex gold nanostructures and a dielectric substrate

Intercoupling of an incident electric field in metal nanoparticles causes asymmetric distribution of surface charges, which eventuates in shifting of the surface plasmon resonance frequency. This feature can be used in tuning the surface plasmon resonance and controlling the light absorption in a desired wavelength. This work provides a theoretical study of the plasmonic properties of complex gold nanostructures on a dielectric substrate where the nanoparticles have different morphologies. For analysis, we have developed a discrete dipole approximation with surface interactions-z, which is the third version of the MATLAB-based DDA-SI toolbox. In this version, lower-upper decomposition of the interaction matrix is used as a preconditioning of the LSQR iterative solver. This method accelerates the DDA-SI calculations by decreasing the total number of iteration steps and decreases the relative residual to achieve more accurate results. In the analysis, nanostructures are assumed to be gold dimers, trimers, and quadrumers with different sizes and elongations of cubical or spherical geometries on a BK7 substrate. The results show that absorption spectra exhibit both red- and blueshifted plasmon resonances in array, depending on the particle shape and elongation. The cubic structure of gold array provides the highest absorption efficiency, while the spherical structures give wider bandwidth; the combination of these structures could be used to design a system with intended features. We demonstrate that the geometrical symmetry plays an important role in the plasmon resonance of gold arrays, and it is shifted when the symmetry of the array is broken.

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.

Gold Nanowires-Based Hyperbolic Metamaterial Multiband Absorber Operating in the Visible and Near-Infrared Regimes

Spectral feature of gold nanowires-based hyperbolic metamaterial (NWHMM) absorber was investigated. The absorber has NWHMM surface as the top layer, which is composed of periodically arranged arrays of subwavelength-sized gold (Au) nanowires (of circular cross-section) immersed in silicon dioxide (SiO2) dielectric medium. Such NWHMM surface is over a planar dielectric SiO2 substrate, backed by a perfect (bottom) reflector comprised of nano-sized bulk layer of silver (Ag). Considering the incidence of electromagnetic waves (in the range of 400–1400 nm wavelength) on the top NWHMM surface, the absorption spectrum of the proposed structure was analyzed for different thickness values (of surface), incidence angles, and also Au nanowire radius. The presence of multiple absorption peaks was noticed, which comes into existence due to different resonance conditions. The absorption features can be tuned by altering the operational conditions.

Evaluation of herringbone carbon nanotubes-modified electrodes for the simultaneous determination of ascorbic acid and uric acid

An array of gold interdigitated microelectrodes (Au-IDA) has been modified by casting herringbone carbon nanotubes (hCNTs) producing a new electrochemical sensor suitable for the simultaneous determination of ascorbic acid (AA) and uric acid (UA) in PBS (0.25 M, pH 7.0). The sensor showed good electrocatalytic properties for both analytes with low working potentials, linear ranges between 0 and 600 μM for AA, and between 0 and 420 μM for UA. The empirical limits of detection (LODs) and the limits of quantification (LOQs) for both analytes were 15 μM and 50 μM, respectively. Moreover, UA does not interfere in the measurement of AA and vice versa. Furthermore, the presence of common analytes in physiological fluids as glucose, dopamine and epinephrine do not interfere in the quantification neither AA nor UA.

Sub-wavenumber linewidth mid-infrared notch filter enabled by a dual-period plasmonic structure

Abstract A transmission notch filter based on surface-plasmon resonance is proposed and numerically studied in the mid-infrared region. The metal structure is a dual-period grating constructed by using smaller-period gold arrays as the duty portions of a larger-period grating. The plasmonic filter shows high transmission of >85% over broad mid-infrared range, and a single notch at ∼ 4. 073 μ m with 24 dB extinction ratio. The stop bandwidth of the filter is ∼ 0.75 nm ( ∼ 0.45 cm−1), corresponding to the quality factor as high as 5400, which is improved by at least one order of magnitude. The rejection wavelength and bandwidth of the filter can be designed by adjusting the structure parameters. Additionally, the angle and polarization of the incidence and refractive index of the surrounding medium affect the performance of the filter.

Single-layer graphene-coated gold chip for enhanced SPR imaging immunoassay

Surface plasmon resonance imaging (SPRi) is a powerful tool for label-free, real-time and high-throughput immunoassay, but its sensitivity needs essential improvement. It has been recently reported that the sensitivity of angular-interrogation surface plasmon resonance (SPR) could be efficiently enhanced on single-layer graphene-coated gold chip. The usefulness of this method however remains unclear for reflectivity-based SPRi platform. Herein for the first time we demonstrate that the graphene coating-enabled intrinsic sensitivity enhancement is applicable to high-throughput SPRi and the enhancement factor is further quantitatively evaluated. High-quality single-layer graphene is transferred in a site-controllable manner to cover half of spots on the SPRi gold array chip. With anti-zearalenone (ZEN) antibody as a model target and polydopamine (PDA) thin film as a reactive layer for probe immobilization, the SPRi detection signals on two types of sensing spots are quantitatively compared on a single chip and the enhancement factor is evaluated. It is unambiguously disclosed that on the reflectivity-based SPRi platform, single-layer graphene coating results in a ca. 40% enhancement on the detection signal (reflectivity increase, ΔR). This work unveils the compelling SPRi sensitivity enhancement of graphene coating and may facilitate its broad practical applications.

A sensitive electrochemical immunosensor for label-free detection of Zika-virus protein

This work, as a proof of principle, presents a sensitive and selective electrochemical immunosensor for Zika-virus (ZIKV)-protein detection using a functionalized interdigitated micro-electrode of gold (IDE-Au) array. A miniaturized IDE-Au immunosensing chip was prepared via immobilization of ZIKV specific envelop protein antibody (Zev-Abs) onto dithiobis(succinimidyl propionate) i.e., (DTSP) functionalized IDE-Au (electrode gap/width of 10 µm). Electrochemical impedance spectroscopy (EIS) was performed to measure the electrical response of developed sensing chip as a function of ZIKV-protein concentrations. The results of EIS studies confirmed that sensing chip detected ZIKV-protein selectively and exhibited a detection range from 10 pM to 1 nM and a detection limit of 10 pM along with a high sensitivity of 12 kΩM−1. Such developed ZIKV immune-sensing chip can be integrated with a miniaturized potentiostat (MP)-interfaced with a smartphone for rapid ZIKV-infection detection required for early stage diagnostics at point-of-care application.

Gold surface plasmon crystal structure based-on polystyrene template for biosensor application.

In this communication, we assembled ordered polystyrene (PS) microsphere array as a template with the drop-coating method, and the oxygen plasma was used to etch the template to adjust the spacing between the PS microspheres. Nano-triangular gold array and silver nano-pyramid array were obtained by ion beam sputtering to deposit precious metal gold and silver. We observed the surface morphology of Au and Au/Ag composite films by scanning electron microscope and characterized the films by X-ray diffraction and ultraviolet/visible light spectrophotometer. The results show that the etching time of oxygen plasma has an obvious effect in adjusting the spacing between PSs and has a significant effect on the morphology of Au structure.

Gold nanochestnut arrays as ultra-sensitive SERS substrate for detecting trace pesticide residue

In comparison to conventional spectroscopic techniques based on chromatography, surface-enhanced Raman spectroscopy (SERS) enables the rapid identification and detection of trace pesticide residues present in trace amounts in the environment and foods. Herein, a facile approach to fabricate unique gold nanochestnuts (GNCs) as an ultra-sensitive SERS substrate for detecting trace pesticide residues has been developed based on anodic aluminum oxide (AAO) templates. The GNCs are synthesized through the galvanic replacement of Ag on the top of Ni nanorod arrays. The as-prepared GNCs have well-controlled structural parameters, and importantly have unique anisotropic morphologies that benefit the enhancement in SERS performance. As a result, rhodamine 6 G (R6G) can be efficiently detected with GNCs as the SERS substrate even with a concentration of only 10−12 M, and the Raman enhancement factor reaches up to 5.4 × 109 at this concentration. Further SERS measurement of thiram indicates a remarkable SERS-active sensitivity of the as-prepared GNCs with a detection limit of thiram up to 10−14 M. The GNCs also exhibit a high signal-to-noise ratio.

Comparing the effect of different surfactants on the aggregation and electrical contact properties of graphene nanoplatelets

We report the influence of different surfactants, Triton X-100, sodium dodecyl sulfate (SDS) and cetrimonium bromide (CTAB), on the suspended graphene nanoplatelets (GNPs) in aqueous solution studied via a single entity electrochemical technique. This method simply requires recording the current responses resulting from the impacts of individual and aggregated GNPs with an interdigitated gold electrode array. Upon impact the nanomaterial can bridge across two interdigitated gold microbands creating an electrical contact. The current magnitude reflects both the agglomeration state of the material and the contact resistance between the gold array and the carbon nanomaterial. The sensitivity of the magnitude of the current steps to the identity of the used surfactant was further evidenced, indicating the influence of these surfactants upon the electrical connectivity of the nanomaterial to the electrode substrate.

Gold Bowtie-Shaped Dimer Arrays in a Stretchable Substrate with Tunable LSPR

We proposed and demonstrated a gold bowtie-shaped dimer array semi-buried in a deformable polymer substrate. The wavelength tunability of coupled bonding localized surface plasmon resonance modes with different polarizations was confirmed by stretching simulations and experiments. The tuning operations were reconfigurable and reliable under applied elongations of up to 50%.

Photoelectrochemical reactivity of well-defined mesoscale gold arrays on SiO2/Si substrates in CO2-saturated aqueous electrolyte

In this article we present a study on the influence of the size of mesoscopic gold nanostructures on silicon (Si) with well-defined geometry on their reactivity towards hydrogen evolution and carbon dioxide reduction. The onset potential for these two reactions decreases by 170 mV with structure size decreasing from 1400 nm to 75 nm, whereby hydrogen evolution is accelerated somewhat more than carbon dioxide reduction. This effect is independent of the doping type and level of the substrate, i.e. it occurred for moderately doped p-type Si (p-Si) under illumination, as well as on n-type (n-Si) and degenerately doped p-type Si (p++-Si) in the dark. Therefore, the increase in reactivity is not influenced by the metal/semiconductor contact which changes from Schottky-type for p-Si to ohmic for p++-Si. Due to the relatively large structure size, quantum confinement and a change in surface defect density do not play a role. We argue that the role of the metal structure edges, which increases with decreasing structure size, is decisive. At the edges, the electrostatic charge and potential distribution as well as the chemical environment are different compared to the conditions at the interior surface. At present it remains unclear whether the reactivity enhancement is predominantly due to an electrostatic effect or a chemical, bifunctional mechanism.

Gold nanocone arrays directly grown on nickel foam for improved SERS detection of aromatic dyes

An efficient SERS substrate composed of gold nanocone arrays with abundant sharp tips directly grown on 3D porous Ni foam (AuNCA@Ni foam) was developed for sensitive detection of aromatic dyes.

Gold nano-elliptic arrays used in plasmonic waveguides in near infrared spectrum

Gold nano-elliptic arrays used in plasmonic waveguides in near infrared spectrum

Оптические эффекты в магнитных гиперболических метаматериалах

Abstract —We present the results of synthesis of arrays of gold and bilayer Au/Ni nanorods in a matrix of porous anodic alumina and of experimental investigation and numerical simulation of their optical and magnetooptical properties. We show that the spectra of these structures have two singular features located near 520 nm and in the range of 700–800 nm. Au/Ni nanorods exhibit a significant modulation and enhancement of the magnetooptical intensity effect in the range of the long-wavelength resonance. Experimentally observed features agree with results of numerical simulation.

Surface-enhanced Raman scattering active gold nanoparticle/nanohole arrays fabricated through electron beam lithography

Effective surface-enhanced Raman scattering (SERS)-active substrates from gold nanoparticle and gold nanohole arrays were successfully fabricated through electron beam lithography with precise computer-aided control of the unit size and intergap distance. Their SERS performance was evaluated using 4-mercaptobenzoic acid (4-MBA). These gold arrays yielded strong SERS signals under 785 nm laser excitation. The enhancement factors for 4-MBA molecules on the prepared gold nanoparticle and nanohole arrays maxed at 1.08 × 107 and 8.61 × 106, respectively. The observed increase in SERS enhancement was attributed to the localized surface plasmon resonance (LSPR) wavelength shifting toward the near-infrared regime when the gold nanohole diameter increased, in agreement with the theoretical prediction in this study. The contribution of LSPR to the Raman enhancement from nanohole arrays deposited on fluorine-doped tin oxide glass was elucidated by comparing SERS and transmission spectra. This simple fabrication procedure, which entails employing electron beam lithography and the controllability of the intergap distance, suggests highly promising uses of nanohole arrays as functional components in sensing and photonic devices.

Fabrication of highly ordered 2D metallic arrays with disc-in-hole binary nanostructures via a newly developed nanosphere lithography

2D metallic arrays with binary nanostructures derived from a nanosphere lithography (NSL) method have been rarely reported. Here, we demonstrate a novel NSL strategy to fabricate highly ordered 2D gold arrays with disc-in-hole binary (DIHB) nanostructures in large scale by employing a sacrificing layer combined with a three-step lift-off process. The structural parameters of the resultant DIHB arrays, such as periodicity, hole diameter, disc diameter and thicknesses can be facilely controlled by tuning the nanospheres size, etching condition, deposition angle and duration, respectively. Due to the intimate interactions between two subcomponents, the DIHB arrays exhibit both an extraordinary high surface-enhanced Raman scattering enhancement factor up to 5 × 108 and a low sheet resistance down to 1.7 Ω/sq. Moreover, the DIHB array can also be used as a metal catalyzed chemical etching catalytic pattern to create vertically-aligned Si nano-tube arrays for anti-reflectance application. This strategy provides a universal route for synthesizing other diverse binary nanostructures with controlled morphology, and thus expands the applications of the NSL to prepare ordered nanostructures with multi-function.

Gold nano disks arrays for localized surface plasmon resonance based detection of PSA cancer marker

Here in, we report prostate specific antigen (PSA) detection method using DNA aptamer functionalized gold nano disks array. The approach is based on DNA aptamer–PSA specific interaction and the localized surface plasmon resonance (LSPR) extinction λ max shifts of the transmitted light (UV–vis). The specific interaction results in a stable dynamic equilibrium. The concentration effect on equilibrium time has been described. We also describe the relationship between the aptamer concentration and the plasmon response. Using 2nM DNA aptamer on gold nano arrays, a detectable linear range from 1.7ng/mL to 20.4ng/mL was obtained with the R2 value>0.99. The limit of detection (LOD) value was found 1.49ng/mL. Finite difference time domain (FDTD) simulations were plotted for the gold substrate in air and water. Great agreement was found between the experimental and simulated shifts in both the cases. The refractive index sensitivities (S) of experimental spectra (113nm/RIU) and simulated spectra (116nm/RIU) were also found in good agreement. These results indicate that this NanoPlasmonic Sensing (NPS) detection platform is most suitable for the pre-biopsy test of prostate cancer patients. The DNA aptamers have been used as specific receptors for biomarkers for the first time; it provided the method with great potential for monitoring other biological interaction due to its great versatility and resistance to denaturation. Furthermore, substrate is recoverable which gives it clear advantage over most of the prevalent methods.

Plasmonic Photovoltaic Cells with Dual-Functional Gold, Silver, and Copper Half-Shell Arrays.

Solid-state photovoltaic cells based on plasmon-induced charge separation (PICS) have attracted growing attention during the past decade. However, the power conversion efficiency (PCE) of the previously reported devices, which are generally loaded with dispersed metal nanoparticles as light absorbers, has not been sufficiently high. Here we report simpler plasmonic photovoltaic cells with interconnected Au, Ag, and Cu half-shell arrays deposited on SiO2@TiO2 colloidal crystals, which serve both as a plasmonic light absorber and as a current collector. The well-controlled and easily prepared plasmonic structure allows precise comparison of the PICS efficiency between different plasmonic metal species. The cell with the Ag half-shell array has higher photovoltaic performance than the cells with Au and Cu half-shell arrays because of the high population of photogenerated energetic electrons, which gives a high electron injection efficiency and suppressed charge recombination probability, achieving the highest PCE among the solid-state PICS devices even without a hole transport layer.