Gold Nanowire Arrays Research Articles

Closed Bipolar Nanoelectrode Array for Ultra-Sensitive Detection of Alkaline Phosphatase and Two-Dimensional Imaging of Epidermal Growth Factor Receptors.

The combination of closed bipolar electrodes (cBPE) with electrochemiluminescence (ECL) imaging has demonstrated remarkable capabilities in the field of bioanalysis. Here, we established a cBPE-ECL platform for ultrasensitive detection of alkaline phosphatase (ALP) and two-dimensional imaging of epidermal growth factor receptor (EGFR). This cBPE-ECL system consists of a high-density gold nanowire array in anodic aluminum oxide (AAO) membrane as the cBPE coupled with ECL of highly luminescent cadmium selenide quantum dots (CdSe QDs) luminophores to achieve cathodic electro-optical conversion. When an enzyme-catalyzed amplification effect of ALP with 4-aminophenyl phosphate monosodium salt hydrate (p-APP) as the substrate and 4-aminophenol (p-AP) as the electroactive probe is introduced, a significant improvement of sensing sensitivity with a detection limit as low as 0.5 fM for ALP on the cBPE-ECL platform can be obtained. In addition, the cBPE-ECL sensing system can also be used to detect cancer cells with an impressive detection limit of 50 cells/mL by labeling ALP onto the EGFR protein on A431 human epidermal cancer cell membranes. Thus, two-dimensional (2D) imaging of the EGFR proteins on the cell surface can be achieved, demonstrating that the established cBPE-ECL sensing system is of high resolution for spatiotemporal cell imaging.

Design of a high-resolution magneto-plasmonic biosensor for analyte detection

This paper introduces the design of a magneto-plasmonic refractometric sensor aimed at achieving high resolution. This sensor consists of arrays of gold nanowires and layers of SiO2 and Co6Ag94, where the analyte is placed on the gold nanowires. A p-polarized optical field with a wavelength of 631 nm is used to excite the structure, which is applied in the range of 1° to 45°. A magnetic field is applied to z-axis to create the magneto-optical effect. The reflected optical field of the samples is used to calculate the signal of the transverse magneto-optical Kerr effect, which shows significant changes in the refractive index of the samples and the direction of the magnetic field. The highest displacement is 4°. The highest value of the figure of merit is 3611 RIU−1, and the maximum sensitivity is obtained as 71 °/RIU.

Gold nanowires-based sensor for quantification of H2O2 released by human airway epithelial cells

Hydrogen peroxide (H2O2) is a biomarker relevant for oxidative stress monitoring. Most chronic airway diseases are characterized by increased oxidative stress. To date, the main methods for the detection of this analyte are expensive and time-consuming laboratory techniques such as fluorometric and colorimetric assays. There is a growing interest in the development of electrochemical sensors for H2O2 detection due to their low cost, ease of use, sensitivity and rapid response. In this work, an electrochemical sensor based on gold nanowire arrays has been developed. Thanks to the catalytic activity of gold against hydrogen peroxide reduction and the high surface area of nanowires, this sensor allows the quantification of this analyte in a fast, efficient and selective way. The sensor was obtained by template electrodeposition and consists of gold nanowires about 5 μm high and with an average diameter of about 200 nm. The high active surface area of this electrode, about 7 times larger than a planar gold electrode, ensured a high sensitivity of the sensor (0.98 μA μM−1cm−2). The sensor allows the quantification of hydrogen peroxide in the range from 10 μM to 10 mM with a limit of detection of 3.2 μM. The sensor has excellent properties in terms of reproducibility, repeatability and selectivity. The sensor was validated by quantifying the hydrogen peroxide released by human airways A549 cells exposed or not to the pro-oxidant compound rotenone. The obtained results were validated by comparing them with those obtained by flow cytometry after staining the cells with the fluorescent superoxide-sensitive Mitosox Red probe giving a very good concordance.

Conformal coating of CdS onto flexible enokitake-like standing gold nanowire arrays for omnidirectional low-light-intensity photocatalysis

Nature’s photocatalysis system is typically flexible and can function with omnidirectional sunlight illumination (e.g. plant leaves), sometimes even under low-intensity sunlight conditions (e.g. seagrass). Previous research efforts have been mainly directed at designing photocatalysts in solutions or on rigid substrates with the aim of achieving high efficiency rather than mimicking the features of ubiquitous natural biosystems. Here we report on flexible artificial leaves by using elastomer-bonded, CdS-coated, enokitake-like gold nanowire (AuNW) arrays, which can perform model chemical reactions under omnidirectional light illumination and at a low light intensity of ∼1.2 mW/cm2 – about 1% of the sunlight energy at the sea surface level, which corresponds to the disphotic zone in the sea. The key attributes of our photocatalytic system include: (1) closely-packed, vertically aligned AuNWs offering high surface area and efficient light absorption; (2) the conformal and tunable deposition of CdS onto AuNWs enabling optimization of photocatalytic efficiency; (3) free-standing and flexible features allowing for a versatile design that mimics Nature’s photocatalytic process.

Highly Bright Gold Nanowires Arrays for Sensitive Detection of Urea and Urease.

In this work, highly fluorescent gold nanowire arrays (Au NWs) are successfully synthesized by assembling Zn2+ ions and non-emissive oligomeric gold-thiolate clusters using mercaptopropionic acid both as a reducing agent and a growth ligand. The synthesized Au NWs exhibited strong bluish green fluorescence with an absolute quantum yield up to 32% and possessed ultrasensitive pH stimuli-responsive performance in the range of 7.0-7.8. Based on the excellent properties of the as-prepared nanowire arrays, we developed a facile, sensitive, and selective fluorescent method for quantitative detection of urea and urease. The fabricated nanoprobe showed superior biosensing response characteristics with good linearities in the range of 0-100 μM for urea concentration and 0-12 U/L for urease activity. In addition, this fluorescent probe afforded relatively high sensitivity with the detection limit as low as 2.1 μM and 0.13 U/L for urea and urease, respectively. Urea in human urine and urease in human serum were detected with satisfied results, exhibiting a promising potential for biomedical application.

High-Q localized surface plasmon resonance based on bound states in the continuum for enhanced refractive index sensing.

Nanophotonics based on localized surface plasmon resonance (LSPR) has emerged as a vibrant arena for research into enhanced light-matter interactions with potential applications in imaging, sensing, and computing. However, the low quality (Q) factor of LSPR is a significant barrier to comprehensive device applications. Here, we demonstrate that coupling the LSPR of a gold nanowire array with the optical bound states in the continuum (BIC) of a dielectric double-layer grating can significantly increase the Q factor of LSPR. We realize two hybrid modes with Q factors of up to 111 at 558 nm and 83 at 582 nm, which are about 14 and 10 times larger than those of an uncoupled gold nanowire array. Based on temporal coupled-mode theory, we further show that the resonance frequencies and Q factors of the hybrid modes can be modulated and optimized by varying relevant structural parameters. This coupled system provides a new platform for improving the figures of merit (FoMs) of LSPR-based refractive index sensors, and the concept of LSPR-BIC coupling can be extended to other similar nanosystems.

Acoustic graphene plasmon resonator based on gold nanowire arrays.

An acoustic graphene plasmon (AGP) resonator based on gold nanowire arrays structure is proposed in this paper. The resonator is designed by continuous graphene layer/gold nanowire arrays/optical resonant cavity. The infrared light excites the AGP in the graphene/gold arrays structure and propagates along the graphene surface. The coupling efficiency can be improved by the optical resonator cavity. The finite-difference time-domain method is used to simulate and optimize the property of the resonator. The results show that the resonator has a stronger optical limiting effect and higher coupling efficiency. The AGPs are a prospective platform that enhances light-matter interactions, reduces spread loss, and exhibits a double resonance absorption phenomenon in the studied mid-infrared wavelength range. The research results provide a basis for the design of optoelectronic devices and more.

Coupled localized surface plasmon resonances in periodic arrays of gold nanowires on ion-exchange waveguide technology

Coupled localized surface plasmon resonances (LSPRs) in periodic arrays of metallic nanowires are attractive for use in sensing applications due to their light enhancement and their sensitivity to the surrounding environment. Due to the interwire coupling, they behave as plasmonic waveguides with high wavevector modes that require bulky methods for efficient excitation. In this contribution, we demonstrate the excitation of coupled LSPRs in gold nanowires with photonic modes supported by an optical waveguide made with ion exchange technology. Currently, although weakly-coupled LSPRs are experimentally demonstrated, strongly-coupled LSPRs are only demonstrated numerically due to the challenge represented by the fabrication of a high density nanowire array with current electron beam lithography. Due to their operation across the visible spectrum and its low-loss coupling to standard optical fibers, integrated nanowires on glass waveguides open new perspectives for the development of hybrid photonic-plasmonic integrated optical devices.

Association between Cell Microenvironment Altered by Gold Nanowire Array and Regulation of Partial Epithelial‐Mesenchymal Transition

AbstractCell microenvironment is an essential factor in determining cell growth and cell fate. Many studies have been carried out to understand the functions and mechanisms of small molecules or growth factors/cytokines; however, the effects of the physical environment on cells are relatively unknown. Changes in the cell's physical microenvironment affect cell adhesion and modify intracellular signaling controlled by adhesion properties, resulting in altering the cytoskeletal structure and cellular properties. Herein, it is demonstrated that the changes in cell adhesion can affect the epithelial‐mesenchymal transition (EMT) of epithelial cells by implementing a cell microenvironment with a gold (Au) nanowire array to influence cell adhesion. A forcible decrease in cell adhesion leads to the downregulation of epithelial biomarkers and the upregulation of mesenchymal biomarkers. The results of force‐distance experiments using atomic force microscopy showed that the overall stiffness of epithelial cells declined similarly to the case for mesenchymal‐like cells. With this comprehensive analysis of cellular properties, a physical microenvironment for cell adhesion alteration is suggested, that can induce mesenchymal characteristics in both epithelial and mesenchymal cells through partial EMT.

Nanowire-based metamaterial for antireflective applications

In this paper, we introduce a hexagonal array of vertical gold nanowires with enhanced antireflective properties in the UV-Vis and near-IR wavelengths. The array reduces the reflectance of the underlying silicon wafer, based on the plasmonic resonances that metals exhibit at the nanoscale. The design is optimized with the particle swarm optimization algorithm, an evolutionary algorithm able to drive the morphology of a nano-object towards an optimum. The nanowires' optical properties are evaluated with numerical simulations. The reflectance of the optimized array decreases 100%, mainly in the visible wavelengths, unveiling its potential as an antireflective coating.

Carboxylic Acid-Functionalized, Graphitic Layer-Coated Three-Dimensional SERS Substrate for Label-Free Analysis of Alzheimer’s Disease Biomarkers

Surface-enhanced Raman spectroscopy (SERS)-based protein analysis is a promising alternative to existing early stage diagnoses. However, SERS research conducted thus far accompanies challenges such as nonuniformity of plasmonic nanostructures, irregular coating of analytes, and denaturation of proteins, which seriously limit the practicability of suggested approaches. Here, we introduce a carboxylic acid-functionalized and graphitic nanolayer-coated three-dimensional SERS substrate (CGSS) fabricated by sequential nanotransfer printing. The substrate consists of well-defined, uniform gold nanowire arrays for effective Raman signal enhancement and a strong protein-immobilization layer. With an enhancement factor (EF) of 5.5 × 105, on par with the highest ever reported values, the CGSS allows the detection of protein conformational changes and the determination of protein concentration via Raman measurements. Exploiting the CGSS, we successfully measured the SERS spectra of Alzheimer's biomarkers, tau protein and amyloid β, based on which secondary structural changes were analyzed quantitatively.

Atomistic treatment of periodic gold nanowire array nanofasteners under shear loading

Comprehensive molecular dynamics simulations are conducted to unravel the mechanics and mechanisms associated with the strength and fracture behavior of a highly ordered gold nanowire (Au-NW) array of a pair of nanofasteners (nanoconnectors) under externally applied shear strain. Large-scale atomic/molecular massively parallel simulator (LAMMPS and embedded atom method were adopted to model the atomic interactions of a number of neighboring nanofasteners. This was affected via the use of a periodic simulation box around a pair of highly ordered nanotube arrays to minimize the cost of the computations. Energy minimization using a conjugate gradient algorithm was first performed and followed by atomic relaxation to achieve an equilibrated configuration under the canonical ensemble of constant temperature and volume. The relaxed equilibrated configuration of the nanofastener was then subjected to an externally applied shear strain at a rate of per nanosecond under the canonical ensemble. Our results reveal the importance of the morphology and the overlap depth of the mating nanowire arrays upon the mechanical and fracture behavior of the nanofastener under shear loading. Our work also disclosed the phenomenon of multiple contacts of some displaced nanowires with their neighbors even after their fracture leading to multiple cold-welds with added redundancy to the nanofastener. Finally, in this research, we identified the locations of dislocation emissions and the resulting fracture processes that govern the mechanical integrity and ultimately the functionality of the Au-NW connector. The proposed highly ordered alignment, as conceived numerically herein, can yield a peak stress two to three times higher than that corresponding to a random alignment reported in a previous study. The Au-NW connector also exhibited resistance to fracture, even in cases where small overlap depth is considered in joint bonding. The nanoconnector was also tested at high temperatures (up to 450 K). Our results show that the rising temperature only leads to a minor reduction in the load transmitted by the nanoconnector.

Footprint of plexcitonic states in low-power green–blue plasmonic random laser

Green–blue plasmonic random laser is attained by two-dimensional plexcitonic structure. The main gain plexcitonic media contained two-dimensional periodic arrays of gold nanowires which is covered by dye layer. Due to the change in the strength of exciton and plasmon coupling in these plexcitonic gain structures, different close loop, and thus random lasing must be takes place. For this purpose, we fabricate six samples with different plexcitonic power and pumped fabricated two-dimensional nanostructures by green nanosecond pulsed laser. Our results show efficient coherent random lasing due to the plexcitonic nanostructure in the blue, because two-photon absorption and also green part of the visible spectral region considering its applicability in the design and fabrication of compact and miniaturized random laser sources.

T61SUICIDE DEATHS SELECTED FOR GENETIC RISK: POLYGENIC RISK SCORE CHARACTERISTICS AND HIGH-IMPACT SEQUENCE VARIANTS

Plasmon lasers can support ultrasmall mode confinement and ultrafast dynamics with device feature sizes below the diffraction limit. At present in the single visible light frequency, the optical gain method of constraint SPP on metal nanowires structure reported less. We design the gold nanowire array structure, consisting of PMMA and R6G dye molecules as gain, by 488 nm pump in the middle of the nanowires position for wide range of light, use symmetry broken overcome that momentum does not match the photonic and SPP energy conversion. Theoretical analysis shows that dyes provide coherent optical feedback, resulting in nanowires face will observe laser properties of surface plasmons. Feature analysis: the incident light and pump joint strength is greater than the sum of strength which is the incident light, pump respectively. Under the effect of dye molecules gain effective, length of SPP transmission can increase 1 µm. The results achieved in a single optical frequency of stimulated radiation, application of dye optical gain can achieve continuous gain effect. This is for the future development of plasma amplifier and the wavelength laser.

1-nm-Wide Hydrated Dipole Arrays Regulate AuNW Assembly on Striped Monolayers in Nonpolar Solvent

Summary We show that striped phases of horizontally oriented phospholipids presenting 1-nm-wide orientable dipole arrays can order and straighten flexible 2-nm-diameter gold nanowires (AuNWs) with lengths (up to 1 μm) that greatly exceed the template pitch (∼7.5 nm). AuNW ordering can extend over areas > 100 μm2. Whereas wires bundle in solution, with contact between ligand shells, wires adsorbing to the template separate to much larger center-to-center distances (e.g., 12–30 nm) near multiples of the template pitch, consistent with repulsive interactions between wires emerging during interactions with dipole arrays in the template. AuNW assembly was carried out in cyclohexane, a nonpolar solvent. Interestingly, we found that wire ordering was contingent on the extent of phospholipid headgroup hydration and the presence of excess oleylamine, which assembled into hemicylindrical micelles around the hydrated headgroups. Together, these components generated a protected polar environment that enabled the phospholipid headgroups to function collectively to regulate AuNW assembly.

Design and development of plasmonic and nanophotonic devices

Research work at Dr. Anuj Dhawan’s laboratory at IIT Delhi is primarily based on the design and development of nanophotonic and plasmonic devices. Dr. Dhawan’s research group has primarily focused on the design and modeling of plasmonic chemical and biological sensors, optical switches, and photonic waveguides and interconnects. In this paper, firstly research work carried out in Dr. Dhawan’s laboratory on sensor devices based on surface plasmon resonance, localized surface plasmon resonance, and surface-enhanced Raman scattering, is described. Subsequently, the research work being carried out in Dr. Dhawan’s laboratory on fabrication of plasmonic nanostructures and their characterization, is discussed. Finally, EM modeling of optical switching devices—consisting of a plasmonic nanostructure system consisting of an array of gold nanowires separated from an underlying gold film by a vanadium dioxide thin film spacer layer—is discussed.

Singular graphene metasurfaces

The spatial tunability of the electron density in graphene enables the dynamic engineering of metasurfaces in the form of conductivity gratings, which can bridge the momentum gap between incident radiation and surface plasmons. Here, we discuss singular graphene metasurfaces, whose conductivity is strongly suppressed at the grating valleys. By analytically characterising their plasmonic response via transformation optics, we first review the physical principles underlying these structures, which were recently found to exhibit broadband, tunable THz absorption. We characterise the spectrum with different common substrates and then move to study in further detail how conductivity gratings may be finely tuned by placing an array of charged gold nanowires at sub-micron distance from the graphene.

Effects of Nanowire Length on Charge Transport in Vertically Aligned Gold Nanowire Array Electrodes.

In this study, we demonstrate that vertically aligned gold nanowire array electrodes provide rapid ion and electron transport to the electrode-electrolyte interface. The charge-transport properties of the nanowire electrodes were investigated through cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy under a constant-volume device configuration. The total charge stored in the corresponding devices increases monotonically with the length of the nanowires owing to the concomitant increase in the electroactive real surface area of the electrode. A remarkable feature of the electrodes is that the internal resistance associated with charge transport decreases with increasing nanowire length. The electric double-layer capacitance per unit electroactive surface area remains constant up to high charge/discharge rates. Our results demonstrate that charge migration occurs rapidly on the surfaces of the nanowires regardless of their length and the charge/discharge rate used. Thus, vertically aligned nanowire array electrodes show promise as current collectors for next-generation electrochemical energy-storage devices.

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.

Plasmonic Biosensor Based on Vertical Arrays of Gold Nanoantennas.

Implementing large arrays of gold nanowires as functional elements of a plasmonic biosensor is an important task for future medical diagnostic applications. Here we present a microfluidic-channel-integrated sensor for the label-free detection of biomolecules, relying on localized surface plasmon resonances. Large arrays (∼1 cm2) of vertically aligned and densely packed gold nanorods to receive, locally confine, and amplify the external optical signal are used to allow for reliable biosensing. We accomplish this by monitoring the change of the optical nanostructure resonance in the presence of biomolecules within the tight focus area above the nanoantennas, combined with a surface treatment of the nanowires for a specific binding of the target molecules. As a first application, we detect the binding kinetics of two distinct DNA strands as well as the following hybridization of two complementary strands (cDNA) with different lengths (25 and 100 bp). Upon immobilization, a redshift of 1 nm was detected; further backfilling and hybridization led to a peak shift of additional 2 and 5 nm for 25 and 100 bp, respectively. We believe that this work gives deeper insight into the functional understanding and technical implementation of a large array of gold nanowires for future medical applications.