Gold Strip Research Articles

The enhanced optical coupling in a quantum well infrared photodetector based on a resonant mode of an air–dielectric–metal waveguide

The hybrid structure consisting of periodic gold stripes and an overlaying gold film is proposed to enhance the optical coupling of a quantum well infrared photodetector. An air–dielectric–metal waveguide is formed when the hybrid structure is integrated on the top of the quantum well detector with the substrate being removed. Finite difference time-domain method is used to numerically obtain the reflection spectrum and the field distribution of the waveguide. The results show that a strong electric field component is induced in parallel to the growth direction of quantum well when the waveguide resonant mode occurs at the detective wavelength of the quantum well infrared photodetector. The relationship between the structural parameters and the resonant wavelength is derived by using the effective refractive index method of the air–dielectric–metal waveguide. A high coupling efficiency can be obtained and the performance of the QWIP can be greatly improved.

Electromagnetic Sensors Based on Magnonic Crystals for Applications in the Fields of Biomedical and NDT

An exploratory investigation of high sensitivity sensors based on magnonic crystals for the measurement of weak magnetic fields at room temperature is presented. The samples are YIG crystals on GGG substrate (Gadolinium-Gallium-Garnet) on which a periodic structure of shallow grooves are etched or gold stripes are deposited. The excitation of surface magnetostatic spin waves (MSSW) which should appear in these structures is obtained by means of microstrip transmission line or microstrip planar antenna.The measurement of the magnonic structure by complex transmission coefficient (S12) shows a significant shift in frequency of the maximum absorption peak related to magnonic band gap which depends on the magnitude of the DC magnetic bias field applied. It shows the possibility of magnonic high Q-value band gap implementation with respect to spin wave propagation band (GHz band) in magnonic crystals applied to spin waves detection of magnetic fields.The influence of the characteristics of the microstrip line or the microstrip antenna on sensor performance (sensitivity and resolution) is studied.

Band structures of surface acoustic waves in nanostructured phononic crystals with defects

The band structures of surface acoustic waves in nanostructured phononic crystals with defects have been studied by Brillouin light scattering and finite-element simulations. The crystals are one-dimensional periodic arrays of alternating gold stripes and air gaps on SiO2/Si substrates, where the periodic defects are gold stripes with non-regular widths. The general features of the band structures are similar to those of the perfect crystal, with the main difference being the appearance of nearly dispersionless defect branches within the bandgap. The defect modes exhibit localization features and are frequency-tunable by varying the defect stripe size.

Time-resolved optical measurement of thermal transport by surface plasmon polaritons in thin metal stripes

We investigate the thermal transport originating from the propagation of surface plasmon polaritons (SPPs) in a thin gold stripe. The SPPs are excited by a grating coupler on the Au stripe which was patterned onto a silicon membrane. The transmissivity changes of the Si membrane due to temperature-induced changes of the interference conditions enable measuring the temperature distribution with temporal and spatial resolution better than 1 μs and 1 μm. With this setup, we demonstrate that SPP excitation, propagation, and decay are accompanied by considerable heating and heat transport.

Multiway Principal Component Analysis for Smartphone Captured Image of Colloidal Gold Strip

Lateral flow test kit has become a popular device for immunoassay of biologically important molecules. Colloidal gold strip has been commercially available for point-of-care clinical testing at hospital or simply at home for self-testing. A method for reading the reaction results of colloidal gold strip assays is proposed. The RGB (red-green-blue) image of a reacted strip is captured by smartphone under natural-light illumination. The two-dimensional grayscale image of each color channel is transformed into nine images by spatially shifting the image in eight adjacent directions. After all three color channel images are transformed, an array including twenty-seven images is constructed. Multiway principle component analysis is then used to the array, extracting texture information of the original image. When the extracted texture is added back to the original image, color of control line and test line regions can be effectively enhanced for reading by naked eyes.

Design of a Rapid Detection of Hepatitis B Immuno Gold Dipstick Test Strip Control System

In response to hepatitis B surface antigen colloidal gold strip rapid analyzer application characteristics, design a new type hepatitis B fast analyzer control system using the embedded method. The control system based on ARM-DSP dual-core architecture, with low power consumption, small volume, anti interference, for hepatitis B surface antigen colloidal gold strip rapid analyzer is miniaturized and portable design foundation.

Surface sensitivity of straight long-range surface plasmon waveguides for attenuation-based biosensing

The sensing performance of straight long-range surface plasmon waveguides consisting of a thin gold stripe embedded in Cytop is explored theoretically as a function of the metal stripe cross-sectional dimensions and the length of the sensing channel, and as a function of the sensing medium refractive index. The surface sensitivity and detection limit of such waveguides for attenuation-based biosensing are assessed. We find that changes in coupling efficiency between the sensing waveguide and the access waveguides, and changes in attenuation constant, due to adlayer formation, can contribute additively to the sensing performance. We observed a trade-off between the insertion loss and the change in insertion loss occurring during sensing. Optimum designs leading to compact, sensitive, and cost-effective biosensors are reported.

Mapping and quantifying electric and magnetic dipole luminescence at the nanoscale.

We report on an experimental technique to quantify the relative importance of electric and magnetic dipole luminescence from a single nanosource in structured environments. By attaching a Eu^{3+}-doped nanocrystal to a near-field scanning optical microscope tip, we map the branching ratios associated with two electric dipole and one magnetic dipole transitions in three dimensions on a gold stripe. The relative weights of the electric and magnetic radiative local density of states can be recovered quantitatively, based on a multilevel model. This paves the way towards the full electric and magnetic characterization of nanostructures for the control of single emitter luminescence.

Interferometry for Ellipso-Height-Topometry part 3: Correction of the aspect errors and reduction of the dispersion of the ellipsometric parameters

Ellipso-Height-Topometry, EHT, is an extended optical topometry, where both the topographies of the surface height H(x,y) and the ellipsometric local parameters Ψ(x,y) and Δ(x,y) of surfaces with locally changing materials are measured on the same pixel raster with high resolution and using the same data sets. Further quantities can be calculated from these measurements on the base of locally confined surface models: the local refractive index, the thickness t(x,y) of overlayers or films, or other parameters of layered systems.In part 1 of this work a z-scanning interferometric scheme with oblique incidence over the entire object field and very useful coherence properties for practical coherence-scanning have been introduced.In part 2, the theory of the ellipsometric parameter acquisition in this interferometer has been developed for isotropic surfaces and the theory for the local segmentation of different materials or such materials covered with films was introduced. The results were verified by two sets of topographies for two different kinds of objects: a grid of gold strips on a substrate of quartz glass and an engine cylinder surface featuring silicon crystals in an aluminium matrix.In this part we deal with the aspect error of the measured profile due to an oblique incidence of the light and the dispersion of the ellipsometric parameters due to the surface roughness and its reduction. The new results are verified by two EHT-sets of topographies for a cast iron surface with graphite laminas.

Gold Decorated Graphene by Laser Ablation for Efficient Electrocatalytic Oxidation of Methanol and Ethanol

AbstractA well‐known limitation in the fabrication of metal‐graphene composite has been the use of surfactants that strongly adsorb on the surface and reduce the performance of the catalyst. We demonstrate here a novel one‐pot synthesis of gold nanoparticles by laser ablation of gold strip and in‐situ decoration on graphene substrate. Not only the impregnation of nanoparticles was linker free, but also the synthesis by itself was surfactant‐free. The composite materials were well characterized morphologically and functionally using electron microscopy, X‐ray and electron diffraction, Raman spectroscopy, Zeta potential, electrochemical measurements and UV‐Visible spectroscopic techniques. This linker‐free gold‐graphene based composite has been employed for catalytic applications pertaining to electrooxidation. We have explored the use of this composite as a binder‐free electrode in electrocatalytic oxidation of methanol and ethanol in alkaline medium. Additionally, the onset potential for ethanol oxidation was found to be more negative, −100 mV, an indication of its promising application in direct ethanol fuel cells.

Enhanced phase sensitivity of metamaterial absorbers near the point of darkness

Plasmonic resonances are accompanied by abrupt phase changes. Utilization of this phase signal and lower phase noises can improve the refractive index resolution of plasmonic sensors. It is shown that the maximal phase change in the frequency domain is achieved at the point of the minimal reflection—the point of darkness. Since the metamaterial absorbers have near zero reflection at their resonance by definition, their phase can be used for sensing purpose. Considered metamaterial absorbers consist of parallel gold strips separated by a dielectric spacer from a thick metallic plate. By the optimization of the spacer thickness and strip widths, and by the adjustment of the angle of incidence, the phase sensitivity above 104 deg/RIU can be achieved in the dynamic range of 2×10−2 RIU.

The enhanced infrared absorption of quantum well infrared photodetector based on a hybrid structure of periodic gold stripes overlaid with a gold film

The hybrid structure of periodic gold stripes overlaid with a gold film is proposed to enhance the infrared absorption of quantum well infrared photodetector. The reflection spectra and the field distributions are numerically calculated by a finite difference time-domain method. The results show that the electric field component perpendicular to the quantum well is strongly enhanced when the plasmonic resonance of the hybrid structure occurs at the operation wavelength of the quantum well infrared photodetector. The effect of the structural parameters on the plasmonic resonant wavelength is discussed, which indicates that the localized surface plasmon as well as surface plasmon polariton plays a role in the light coupling with the hybrid structure. A high coupling efficiency can be obtained with the optimized structural parameters. In addition, the performance of the hybrid structure at the tilted incidence is investigated.

Psilorhynchus khopai, a new fish species (Teleostei: Psilorhynchidae) from Mizoram, northeastern India.

Psilorhynchus khopai, a new species of Psilorhynchidae, is described from Tuisi River, a tributary of Kaladan River, in Mizoram, India. The species is proposed to be a member of the Psilorhynchus homaloptera species group and can be distinguished from its congeners in having a forked caudal-fin with 9 + 9 principal caudal rays, 14-17 predorsal scale rows, 39-41 lateral-line scale rows, mid-lateral body with 9-12 indistinct small dark brown round markings forming a lateral stripe and, in life, a faint gold stripe along dorsal midline with 4-5 black spots between dorsal fin and caudal fin base.

Direct near-field optical imaging of plasmonic interference fields for high-resolution photolithography

The plasmonic interference fields on the sub-wavelength gold gratings were directly investigated by using the collection-mode near-field scanning optical microscopy. For proper designs of structural size and periodicity of gratings, we found the plasmonic interference fields generated in the near filed on the gold strip surface. The light source was a visible laser, with a wavelength of 514nm, illuminating in a normally incident direction to the sample. We demonstrated that the patterns of plasmonic interference fields can reach a narrow linewidth of λ/7, which is considerably beyond the diffraction limit. The examined widths of the near-field intensities achieved 75–90nm on the gold strip surface and 110–120nm on the slit. We also observed that the near-field intensities from both plasmonic interference fields and near-field light of the slits were spatially uniform at the surface, which indicated the capability of near-field intensity redistribution. The numerical simulations by using two-dimensional finite difference time domain (2D-FDTD) method supported the experimental results with excellent consistency. The simulation results also indicated the strong dependences between the plasmon interference fields and polarizations of the incident light. The experimental and simulation results provided the substantial insights for the working mechanism and advanced applications of plasmonic nanopatterns.

Extraction of gold(III) from hydrochloric acid solutions with high-molecular aliphatic alcohols

Experiments on extraction of gold(III) from hydrochloric acid solutions with isomeric aliphatic alcohols containing 6–12 carbon atoms showed that secondary alcohols recover AuCl4− from acid solutions with higher distribution ratios than primary alcohols do. The best alcohol that can be recommended for the extraction of gold(III) from 3–6 M HCl solutions, taking into account the solubility and extraction ability of alcohols, is 2-octanol. The possibility of efficient stripping of gold(III) from the 2-octanol phase with ammonia or thiourea solutions was demonstrated.

Conductive Milieu on Cellular Electromechanics

Cellular polarity and alignment are significant biophysical factors in tissue architectures and tissue-to-organ level functions. Multiple biophysical contributors are addressed as cellular alignment factors in mechanical, biochemical and electrical aspects; however, passive electric conductance has not been discussed. Herein, we report the spontaneous alignment of cardiomyocytes to predefined electric conductivity environments as example. Two to three days after passaging iPSCs-derived cardiomyocytes on thin gold strips (i.e., 10-nm thickness, 10s-µm width and 10s-µm period) patterned on a nonconductive substrate (i.e., glass), the most single-cell cardiomyocytes adhere on the nonconductive area and align themselves parallel to the conductive pattern, without any external stimuli. From control experiments, we can exclude any mechanical cues as the reasons of the spontaneous alignment, such as surface groove and mechanical stiffness. Currently, we hypothesize diamagnetic effect or Frohlich electromagnetic effect as the physiological response of cardiomyocyte, which may be induced from the electric field coupling between cardiomyocytes and the gold pattern. Along with the further understanding, this observation will highlight passive electric elements as important biophysical aspects since many cellular components possess a level of electric properties.

Development of an immunochromatographic kit for rapid detection of human influenza B virus infection.

Type B influenza virus is a major epidemic strain responsible for considerable mortality and morbidity. A colloidal gold immunochromatographic strip for the rapid detection of human influenza B virus was developed. This test is based on membrane chromatography and uses colloidal gold conjugated with influenza B virus anti-NP monoclonal antibody as the tracer. The assembled test strip was housed in a plastic case. The colloid gold strip (CGS) specifically detected all influenza B viruses tested and did not react with other respiratory viruses. Compared with SYBR Green real-time PCR, the sensitivity and specificity of the CGS test was 89.76% and 99.56%, respectively, and the consistency ratio between CGS and real-time PCR was 96.06% in detecting influenza B virus in 710 nasopharyngeal swabs from patients with influenza-like illness in the hospital. The CGS array developed in this study enabled typing of influenza B viruses in human clinical specimens. Thus, together with the advantages of rapid detection and easy operation without requiring specialized personnel and equipment, this technique is a convenient and relatively inexpensive diagnostic tool for large-scale screening of clinical samples.

Transmission of surface plasmon polaritons through atomic-size constrictions

We study the excitation and propagation of surface plasmon polaritons (SPPs) on a micron-sized thin gold stripe. Grating couplers are embedded for both excitation of SPPs and detection after propagation. The experimental setup allows measuring of the decay length of the SPPs on the gold stripe excited in the near infrared part of the electromagnetic spectrum. We show that SPPs are transmitted with a surprisingly high probability across a tapered constriction, with smallest lateral dimensions of atomic size.

Widely tunable thermo-optic plasmonic bandpass filter

We report thermally tunable optical bandpass filters based on long-range surface plasmon polariton waveguides. A thin gold stripe in the waveguide core is surrounded by dielectric layers with dissimilar refractive index dispersions and dissimilar thermo-optic coefficients. High filter transmission is achieved for a wavelength at which the refractive indices of the upper and lower cladding layers are identical, and this spectral point may be changed by varying the filter temperature. Experimentally, over 220 nm of bandpass tuning is achieved around 1550 nm wavelength by varying the device temperature from 19 to 27 °C.

Transfer of thin, patterned gold layers from poly(methyl methacrylate) stamp onto photoresist surface

A simple technique for the transfer of thin gold layer from poly(methyl methacrylate) (PMMA) stamp onto SU-8 photoresist is described and verified. The procedure comprises sputtering of thin gold layer on flat or laser patterned PMMA, bringing the PMMA stamp into contact with photoresist substrate, transferring of the gold layer onto photoresist and finally dissolution of the PMMA stamp. Surface morphology of as sputtered and transferred gold layers was determined by profilometry, confocal microscopy, and atomic force microscopy (AFM) techniques at three different scales. Electrical properties were examined by conductive AFM technique. The transfer from patterned PMMA stamp leads to simultaneous patterning of the gold layer and creation of a system of ordered conductive gold strips separated by non-conductive areas on photoresist surface.