Gold Rods Research Articles

Tunable lattice-induced transparent metasurface for dynamic terahertz wave modulation.

Tunable metasurfaces offer a promising avenue for dynamically modulating terahertz waves. Phase-change materials are crucial in this dynamic modulation, enabling precise and reversible control over the electromagnetic properties of the metasurfaces. In this study, we designed and experimentally fabricated a tunable lattice-induced transparent metasurface. This metasurface comprises two gold rod resonators exhibiting different periodic distributions, each supporting an electric dipole resonance at 2.03 THz and a surface lattice resonance at 1.51 THz, respectively. By combining these structures, we realize lattice-induced transparency. Simulation results show that the phase change of Ge2Sb2Te5 modulates these resonances, with the crystalline state significantly weakening their resonance strength intensity. The maximum modulation depth of the lattice-induced transparency peak can reach 44.4%. Experimental results of laser-induced GST phase changes confirm a modulation depth of 42.4%. This innovative metasurface design holds promise for applications in terahertz communication systems.

Improving the sensitivity of a plasmonic photonic crystal fiber temperature sensor by introducing an array of nanoscale gold rods

Improving the sensitivity of a plasmonic photonic crystal fiber temperature sensor by introducing an array of nanoscale gold rods

Full-stokes polarization photodetector based on the chiral metasurface with the dislocated double gold rod configurations

The filterless polarization-sensitive optoelectronic device generally has low discrimination, thus severely hindering the development of monolithic full-polarization detectors. We numerically demonstrate a circular polarization photodetector composed of the dislocated 2-bar gold chiral metasurfaces modulating the circular polarization lights and the InGaAs/InP detector chip detecting light intensity signals. The chiral metasurfaces excite the electric field loops with different spins when irradiated with different chiral light, and it explains the high extinction ratios of 21:1 in circularly polarized detectors. In addition, the linear dichroism (LD) and extinction ratios (ER) of the linear polarization device are 0.85 and 80:1, respectively. The excellent ER performance is caused by the boundary state between the metal grating and the InP substrate. The full Stokes pixel based on the six-image-element technique can almost accurately measure arbitrary polarized light at 1550 nm operation wavelength, whose errors of the degree of linear polarizations (Dolp) and the degree of circular polarizations (Docp) are less than −35 dB and −10 dB, respectively.

A multichannel closed bipolar platform to visual electrochemiluminescence sensing of caffeic acid as a model: Potential for multiplex detection

In this study, a fully-featured electrochemiluminescence (ECL) sensing platform based on a multichannel closed bipolar system (closed-BP, C-BP) for the determination of caffeic acid (CA) was successfully developed. The system comprises three individual reservoirs connected to each other by two pairs of gold rods as bipolar electrodes. Moreover, a single pair of gold rods functions as the driving electrodes. Due to configuration consisting of three channels and double-bipolar electrodes, the detection of CA was accomplished in two oxidation and reduction pathways within a single device. Firstly, through close observation of the reactions occurring within the device and utilizing a universal pH indicator and bipolar electrodes, a precise mechanism for the current bipolar systems was initially proposed. Then, the concentration of CA was monitored in the reporting chamber through the following ECL intensities resulting from luminol oxidation and H2O2. The monitoring process was performed using both a photomultiplier tube (PMT) and a digital camera. In the process of analyte oxidation, the PMT and visual (camera)-based detection exhibited a linear response from 5 μmol L−1 to 700 μmol L−1 (limit of detection (LOD) 1.2 μmol L−1) and 50 μmol L−1 to 600 μmol L−1 (LOD 14.8 μmol L−1), respectively. In the analyte reduction pathway, the respective values were 30 μmol L−1 to 450 μmol L−1 (LOD 8.6 μmol L−1) and 55 μmol L−1 to 400 μmol L−1 (LOD 21.2 μmol L−1), for the PMT and visual-based detection, respectively. Our experiments have demonstrated the practical application of the sensor array for efficient and high-performance analysis. This innovative design holds significant potential for diverse fields and paves the way for the development of a user-friendly device.

A plasmonic terahertz perfect absorber based on L-shaped graphene patches and gold rods

A plasmonic terahertz perfect absorber based on L-shaped graphene patches and gold rods

Study of flexible metasurface with gold rod resonators on ploymide substrate in terahertz waveband

A flexible metasurface based on gold rod resonator arrays on a polyimide substrate in the terahertz band is presented. Four different resonator structures with various azimuth angle were designed and investigated. Experimental results demonstrate that the azimuth angle of the gold rod resonators have a significant impact on the terahertz waves under different polarization conditions. Experimental studies on the bending performance reveal that the spectral modulation characteristics of the flexible metasurface is robust within a degree of bending. In addition, the effect of the incident angle on the resonant peaks was investigated, and the redshift of the high-frequency resonant peak was found as the incident angle increases.

Direct Measurement of the Local Density of Optical States in the Time Domain.

One of the most fundamental and relevant properties of a photonic system is the local density of optical states (LDOS) as it defines the rate at which an excited emitter dissipates energy by coupling to its surrounding. However, the direct determination of the LDOS is challenging as it requires measurements of the complex electric field of a point dipole at its own position. We introduce here a near-field setup which can measure the terahertz electric field amplitude at the position of a point source in the time domain. From the measured amplitude, the frequency-dependent imaginary component of the electric field can be determined and the LDOS can be retrieved. As a proof of concept, this setup has been used to measure the partial LDOS (the LDOS for a defined dipole orientation) as a function of the distance to planar interfaces made of gold, InSb, and quartz. Furthermore, the spatially dependent partial LDOS of a resonant gold rod has been measured as well. These results have been compared with analytical results and simulations. The excellent agreement between measurements and theory demonstrates the applicability of this setup for the quantitative determination of the LDOS in complex photonic systems.

Effect of Physiological Fluid on the Photothermal Properties of Gold Nanostructured.

Colloidal gold particles have been extensively studied for their potential in hyperthermia treatment due to their ability to become excited in the presence of an external laser. However, their light-to-heat efficiency is affected by the physiologic environment. In this study, we aimed to evaluate the ability of gold sphere, rod, and star-shaped colloids to elevate the temperature of blood plasma and breast cancer-simulated fluid under laser stimulation. Additionally, the dependence of optical properties and colloid stability of gold nanostructures with physiological medium, particle shape, and coating was determined. The light-to-heat efficiency of the gold particle is shape-dependent. The light-to-heat conversion efficiency of a star-shaped colloid is 36% higher than that of sphere-shaped colloids. However, the raised temperature of the surrounding medium is the lowest in the star-shaped colloid. When gold nanostructures are exited with a laser stimulation in a physiological fluid, the ions/cations attach to the surface of the gold particles, resulting in colloidal instability, which limits electron oscillation and diminishes the energy generated by the plasmonic excitation. Fluorescein (Fl) and polyethylene glycol (PEG) attached to gold spheres enhances their colloidal stability and light-to-heat efficiency; post-treatment, they remand their optical properties.

Towards Perfect Ultra-Broadband Absorbers, Ultra-Narrow Waveguides, and Ultra-Small Cavities at Optical Frequencies.

In this study, we design ultra-broadband optical absorbers, ultra-narrow optical waveguides, and ultra-small optical cavities comprising two-dimensional metallic photonic crystals that tolerate fabrication imperfections such as position and radius disorderings. The absorbers containing gold rods show an absorption amplitude of more than 90% under 54% position disordering at nm. The absorbers containing silver rods show an absorptance of more than 90% under 54% position disordering at nm. B-type straight waveguides that contain four rows of silver rods exposed to air reveal normalized transmittances of 75% and 76% under 32% position and 60% radius disorderings, respectively. B-type L-shaped waveguides containing four rows of silver rods show 76% and 90% normalized transmittances under 32% position and 40% radius disorderings, respectively. B-type cavities containing two rings of silver rods reveal 70% and 80% normalized quality factors under 32% position and 60% radius disorderings, respectively.

Synthesis and Microstructure Influenced Antimicrobial Properties of Dispersed Nanoporous Gold Rods

Synthesis and Microstructure Influenced Antimicrobial Properties of Dispersed Nanoporous Gold Rods

Ge20Sb15Se65 glass-based ultra-bandwidth X-shaped dual-core photonic crystal fiber polarization beam splitter with an air hole filled gold rod

In this paper, a novel X-shaped dual-core photonic crystal fiber polarization beam splitter (X-DC-PCF PBS) with an air hole filled gold rod based on G e 20 S b 15 S e 65 glass is proposed. According to the DC mode coupling theory and surface plasmon resonance effect, the mode coupling phenomena of the x polarization (X-pol) and y polarization (Y-pol) odd and even modes are analyzed, respectively. The variation laws of coupling lengths of the X-pol and Y-pol and the coupling length ratio with different structural parameters at wavelength 1.55 µm are investigated. When the shortest polarization splitting length ( L P S ) is 230 µm, there is only the X-pol and Y-pol light in the cores A and B, respectively. By considering the variation of the extinction ratio and insertion loss (IL) with wavelength, the final polarization splitting bandwidth (PSB) is 358 nm (1.367–1.725 µm), and the maximum ILs of the X-pol and Y-pol in the whole PSB are 0.04 and 0.8 dB, respectively. The proposed X-DC-PCF PBS has ultra-wide PSB, short L P S , and ultra-low IL, so it will play an important role in the development of optical integration technology and the construction of an all-fiber loop platform.

STATIONARY AND ULTRASONIC NANOPARTICLE ASSEMBLY ON NOTABLE SURFACES

Frequently used wettable (SiO[Formula: see text] and nonwettable highly oriented pyrolytic graphite (HOPG) surfaces have been investigated for the deposition and shape separation of gold nanorods and rod–sphere mixture using the droplet evaporation method. In this paper, we explore and compare the resulting assembly using immovable and ultrasonic systems. On HOPG, stable evaporation produces monolayer arrays of gold nanorods on the terraces whereas aligned arrays of nanorods at the step-edges of HOPG. However, isolated large islands of nanorods on the terraces of HOPG and aligned nanorods at the step-edges become chaotic under the ultrasonic deposition. Also besides gold nanorods, excess cetyltrimethylammonium bromide (CTAB) molecules in suspension are deposited on the terraces in the form of mono- and multilayers revealed by an atomic force microscope (AFM). Both stable as well as ultrasonic vibration techniques were employed on the rod–sphere mixture over the SiO2 substrate. Stable drying of a droplet showed order arrays of gold nanorods separated from nanospheres everywhere in the coffee-stain ring. The fascinating assembly has been observed for such suspension deposits obtained under ultrasonic vibrations. Aligned arrays of nanorods covered with CTAB surfactants have been sterically as well as osmotically depleted first nearly all CTAB-coated nanospheres and then self-assembled them with the similar geometries within the coffee-stain ring on the SiO2 surface. The same separation effect has been observed within the initial pinning as well as everywhere over the terraces of the HOPG.

Photonic crystal-based biosensor for detection of human red blood cells parasitized by plasmodium falciparum

In this paper, a biosensors based on a two-dimensional photonic crystal (2D PhC) waveguide including a ring resonator is designed and simulated based on refractive index changes of red blood cells. The proposed biosensor structure consists of an elliptical photonic crystal ring resonator and two linear waveguides containing silicon nitride rods in a 2D rectangular lattice with circular rods. The biosensor is utilized to detect the stages of the Plasmodium falciparum cycle in red blood cells and to diagnose malaria disease. The proposed design distinguishes with high sensitivity between normal red blood cells and cells infected with Plasmodium falciparum. This biosensor is very compact, consists of gold rods in the air background and works very well at two input central wavelengths of 0.514 and 1.55 μm. The finite-difference time-domain (FDTD) method is used to simulate and investigate the device. The biosensor is extremely compact which is very suitable for lab-on-chip applications and exhibits higher sensitivity at both input central wavelengths compared with that of previously reported sensors.

Nano Gold Spheres and Rods: Synthesis and Characterization

The present study aims to synthesised nano gold with chemical method with two shape sphere and rod with multi diameter and aspect ratio and then characterize the synthesised material with Atomic Force Microscope (AFM), Transmission Electron Microscope (TEM) and Ultraviolet-visible (UV–Visible ) spectrophotometer. The AFM and TEM characterization result of three samples for each sphere and rods show that the synthesised material are in nano range with diameter 31.9 nm, 36.19 nm and 79.37 nm respectively for nano sphere and diameters 39.9nm, 36.05 nm and 28 nm respectively for nano-rods samples and the UV-Visible spectrophotometer show that peak of surface plasmon resonance of nano-sphere are at wavelengths 532 nm, 535 nm and 546 nm and all are in the visible range and nano-rod have two peaks one in the visible range at wavelengths 525nm,518nm and 531nm and the other peak is in the near infrared range at wavelengths 633nm, 680nm and 875 nm respectively.

Shape-Dependent Catalytic Activity of Gold and Bimetallic Nanoparticles in the Reduction of Methylene Blue by Sodium Borohydride

In this study the catalytic activity of different gold and bimetallic nanoparticle solutions towards the reduction of methylene blue by sodium borohydride as a model reaction is investigated. By utilizing differently shaped gold nanoparticles, i.e., spheres, cubes, prisms and rods as well as bimetallic gold–palladium and gold–platinum core-shell nanorods, we evaluate the effect of the catalyst surface area as available gold surface area, the shape of the nanoparticles and the impact of added secondary metals in case of bimetallic nanorods. We track the reaction by UV/Vis measurements in the range of 190–850 nm every 60 s. It is assumed that the gold nanoparticles do not only act as a unit transferring electrons from sodium borohydride towards methylene blue but can promote the electron transfer upon plasmonic excitation. By testing different particle shapes, we could indeed demonstrate an effect of the particle shape by excluding the impact of surface area and/or surface ligands. All nanoparticle solutions showed a higher methylene blue turnover than their reference, whereby gold nanoprisms exhibited 100% turnover as no further methylene blue absorption peak was detected. The reaction rate constant k was also determined and revealed overall quicker reactions when gold or bimetallic nanoparticles were added as a catalyst, and again these were highest for nanoprisms. Furthermore, when comparing gold and bimetallic nanorods, it could be shown that through the addition of the catalytically active second metal platinum or palladium, the dye turnover was accelerated and degradation rate constants were higher compared to those of pure gold nanorods. The results explore the catalytic activity of nanoparticles, and assist in exploring further catalytic applications.

Rod–sphere cluster irradiation with femtosecond laser pulses: cut and paste at the nanoscale

Abstract We report on the irradiation of gold rod–sphere assemblies with ultrashort laser pulses, producing structures that are very difficult to obtain by other methods. The optical response of these assemblies displays several peaks arising from the interaction of the plasmon modes of the individual particles, offering thus great flexibility to control the energy deposited on the individual particles. Judicious selection of the wavelength and fluence of the laser pulses allow fine control over the changes produced: the particles can be melted, welded and/or the organic links cleaved. In this way, it is possible to generate structures “à la carte” with a degree of control unmatched by other synthetic protocols. The method is exemplified with gold nanoparticles, but it can be easily implemented on particles composed of different metals, widening considerably the range of possibilities. The final structures are excellent candidates for surface-enhanced spectroscopies or plasmonic photothermal therapy as they have a very intense electric field located outside the structure, not in the gaps.

Design Plasmonic Optical 4 × 2 Encoder Based on 2D Photonic Crystal Ring Resonator

Digital encoders are one of the key devices required in optical communication and digital signal processing systems. In this paper, a new photonic crystal structure is used to design all-optical 4 × 2 encoder constructed from GaAs rods with square lattice in the pentane background based on plasmonic effect. Gold rods have also been used at the interface of dielectric rods and lines defect, which create plasmonic properties into the photonic crystal structure. The designed optical device is composed of four input waveguides and two output waveguides with two ring resonators at the resonant wavelength of 1.14 μm with TM polarization. The presented encoder platform has the small size of 19 μm × 33 μm that makes it to integration into compact all-optical processing systems. The encoder operation is simulated and analyzed with numerical finite-difference time-domain (FDTD) method and plane wave expansion (PWE) method. In the proposed structure, we have shown that by selecting the appropriate radius size for the resonant cavities, the desirable wavelength can be obtained. The maximum values of transmission efficiency for the first and second outputs are 82% and 96%, respectively. Resonant cavities are also located in the crystal lattice in such a way that by activating third input, 50% and 48% of the input signal will be obtained in each output ports indicating (1,1) logic state. So the new plasmonic photonic crystal encoder could be future applicable in the field of optical computing.

A Systematic Investigation of Coupling Between Dark and Bright Polaritons for Infrared Sensing Design

An emerging class of materials for nanophotonics, hyperbolic metamaterials (HMM), opens a wide range of potential technologies. From micro to nano scales, engineering the features of these materials as a function of a host geometry illustrates exotic functionalities. Phonon polaritons (PhPs) with a dielectric host and plasmon polaritons (PPs) with a metallic host are the most common results from light-matter interactions. Accurate analysis enables researchers to engineer unique features, like high dispersion, hence tailored device designs. This work builds upon previous works in this field; the first focused on the possible coupling between PhPs (or the dark modes) and PPs (or the bright modes) whereas the second introduces a mature technique for the analysis. This study explores all possible coupling scenarios between a gold (Au) rod and a hexagonal boron nitride (hBN) rod. In fact, these two materials are established in infrared sensing where Au supports plasmons while hBN provides surface and volume phonons. Varying the geometry of the rods reveals the nature, the distribution, and the coupling of possible modes after analysis. Consequently, a novel procedure for optimal design of IR sensing devices is presented. This numerical platform provides insights into the design of IR sensing structures.

Nanoporous Gold Monolith for High Loading of Unmodified Doxorubicin and Sustained Co-Release of Doxorubicin-Rapamycin.

Nanoparticles (NPs) have been widely explored for delivering doxorubicin (DOX), an anticancer drug, to minimize cardiotoxicity. However, their efficiency is marred by a necessity to chemically modify DOX, NPs, or both and low deposition of the administered NPs on tumors. Therefore, alternative strategies should be developed to improve therapeutic efficacy and decrease toxicity. Here we report the possibility of employing a monolithic nanoporous gold (np-Au) rod as an implant for delivering DOX. The np-Au has very high DOX encapsulation efficiency (>98%) with maximum loading of 93.4 mg cm−3 without any chemical modification required of DOX or np-Au. We provide a plausible mechanism for the high loading of DOX in np-Au. The DOX sustained release for 26 days from np-Au in different pH conditions at 37 °C, which was monitored using UV-Vis spectroscopy. Additionally, we encased the DOX-loaded np-Au with rapamycin (RAPA)-trapped poly(D,L-lactide-co-glycolide) (PLGA) to fabricate an np-Au@PLGA/RAPA implant and optimized the combinatorial release of DOX and RAPA. Further exploiting the effect of the protein corona around np-Au and np-Au@PLGA/RAPA showed zero-order release kinetics of DOX. This work proves that the np-Au-based implant has the potential to be used as a DOX carrier of potential use in cancer treatment.

Molecular Origin of Electrical Conductivity in Gold-Polythiophene Hybrid Particle Films.

Hybrid electronic materials combine inorganic metals and semiconductors with π-conjugated polymers. The orientation of the polymer molecules in relation to the inorganic components is crucial for electrical material properties and device performance, but little is known of the configuration of π-conjugated polymers that bind to inorganic surfaces. Highly curved surfaces are common when using nanoscale components, for example, metal nanocrystal cores covered with conductive polymers. It is important to understand their effect on molecular arrangement. Here, we compare the molecular structures and electrical conductivities of well-defined nanoscale gold spheres and rods with shells of the covalently bound polythiophene PTEBS (poly[2-(3-thienyl)-ethyloxy-4-butylsulfonate]). We prepared aqueous sinter-free inks from the particles and printed them. The particles formed highly conductive films immediately after drying. Films with spherical metal cores consistently had 40% lower conductivities than films based on nanorods. Raman and X-ray photoelectron spectroscopy revealed differences in the gold-sulfur bonds of PTEBS on rods and spheres. The fractions of bond sulfur groups implied differences in the alignment of PTEBS with the surface. More polymer molecules were bound in an edge-on configuration on spheres than on rods, where almost all polymers aligned "face-on" with the metal surface. This leads to different interface resistances: gold-polythiophene-gold interfaces between rods with π-π-tacked face-on PTEBS apparently foster electron transport along the surface-normal direction, while edge-on PTEBS does not. Molecular confinement thus increases the conductivity of hybrid inks based on highly curved nanostructures.