Thin Gold Layer Research Articles

Bioresorbable polylactic acid (PLA) and bioactive glasses (BG) composite: Influence of gold coated of BG powder on mechanical properties and chemical reactivity

Due to the ageing of the population, the synthesis of biomaterials and the optimization of their physico-chemical characteristics are at the heart of many research projects in regenerative medicine. The emergence of 3D printing techniques has rapidly led to the manufacture PLA-BG composite scaffolds using the FFF (Fused Filament Fabrication) technique. However, this composite presents some problems including a lower mechanical strength than the two compounds alone, probably due to the ionic salting-out induced by the BG. This study aims to counter this phenomenon by coating the BG particles with a thin layer of gold. The 3D composite objects will then be characterized mechanically and biologically to ensure that the bioactive character of the composite is preserved.

Bacteria detection in a Kretschmann geometry flow cell at a plasmon-enhanced interface with spectroscopic ellipsometer

In this work, we investigate whether bacteria can be substantially examined in liquid environment with an ellipsometer in the visible wavelength range. For that investigation a Kretschmann type flow cell was used in which the paths of illuminated and reflected light beams are on the substrate side. To enhance the sensitivity a thin gold layer was applied on the top of glass substrate and the measurement was performed by using surface plasmon polaritons. Porphyrin functionalized coating layers were employed to analyze their performance to capture bacteria and to study the stability and repeatability of the optical response with regard to the ellipsometric measurement. Escherichia coli (E. coli) bacteria were used as first model bacteria and their deposition on the sensing surface was monitored in a real-time measurement in a liquid environment.

Dual Tunable Electromagnetically Induced Transparency Based on a Grating-Assisted Double-Layer Graphene Hybrid Structure at Terahertz Frequencies.

We propose a graphene plasmonic structure by applying two graphene layers mingled with a thin gold layer in a silicon grating. By utilizing the finite-difference time-domain (FDTD) method, we investigate the optical response of the system, and observe that the design achieves dual tunable electromagnetically induced transparency (EIT)-like effect at terahertz frequencies. The EIT-like effect arises from the destructive interference between the grapheme-layer bright modes and the gold-layer dark mode. The EIT-like phenomenon can be adjusted by the Fermi level, which is related to the applied voltage. The results show that the group delay of the present structure reaches 0.62 ps in the terahertz band, the group refractive index exceeds 1200, the maximum delay-bandwidth product is 0.972, and the EIT-like peak frequency transmittance is up to 0.89. This indicates that the device has good slow light performance. The proposed structure might enable promising applications in slow-light devices.

Metal-Film-Coated Silica Nanoparticle Monolayers for Application in Surface Enhanced Raman Scattering

Surface enhanced raman scattering is interested for a variety of applications, especially in determining the presence of substances at very low concentrations, at the level of ppm, that is obtained by amplifying the raman scattering signal of adsorbent particles on metal surfaces or nanostructures. In this paper, we report on surface enhanced raman scattering substrates based on metal-film-coated silica nanoparticle monolayer. The silica nanoparticles having the diameter of 196 nm are assembled into close-packaged monolayer on silicon substrate by spin coating technique. The gap among the silica nanoparticles is tuned by HF vapor etching. The investigations on reflectance characteristic and raman spectra show that close- and non-close-packaged monolayers on silicon substrate covered by a thin gold layer can be used as surface enhanced raman scattering substrates.

Prospects for Developing Low-Cost Optical Fiber Sensors for Liquid-Liquid Interface Detection

This work examines the prospects of a low-cost retroreflection optical sensor system for detection of the interface between two immiscible liquids, for applications in oil separation tanks. The sensor in its simplest configuration comprises a bare fiber optic tip, cleaved at an angle of 90º relative to the longitudinal fiber axis. The device tested experimentally is based on a 2x2 bidirectional coupler, which connects the sensor tip to a laser and two photodetectors, one used to measure the signal and the other as a reference. From experiments conducted in a laboratory wateroil system, the measured retro-reflected signal was very small, and of the same order as the differential signal due to low optical contrast liquids. To overcome this difficulty, the detection system was designed with an amplification stage, followed by filtering of the digitally converted signal. With this strategy, an accuracy of 99.7% was reached. On the light of the performance measured by the bare fiber tip configuration, an analysis on the potential improvement in performance obtained, by applying a thin layer of gold to the tip of the sensor, was made. Simulated results indicated that, for an optimized gold film, 13 nm thick, a 13fold improvement in the sensor detection limit is obtained.

Coupled modes enhance random lasing in plasmonic double grating structure

In this work, we experimentally and theoretically proved a flexible fine random laser from a two-face double grating plasmonic structure based on PDMS. Accordingly, PDMS was fabricated using the nanoimprint lithography method and coated by a thin gold layer with a thickness of 35 nm using a PVD device and light-emitting polymer (F8PT) to enhance the scattering and efficiency of the random laser. Using a plasmonic gold grating as a substrate, the simulation results compared the upside and downside of the plasmonic double grating structure. Moreover, an enhancement was observed in light transmission, and it is common to predict high efficiency in random lasing properties. The experimental results showed a comparison between normal plasmonic double grating samples and symmetric and asymmetric double grating -based nanostructures with thicknesses of 200, 400 and 600 μm and reported that random lasing properties had better results for samples with thinner spaces based on coupled mode effects. Correspondingly, this was done by increasing the intensity and decreasing the lasing threshold from 22 μJ in normal double grating to 16 μJ in the thinnest double grating structure.

Dual-source powered nanomotor with integrated functions for cancer photo-theranostics

While the miniaturization and motility of artificial nanomotors made them popular tools for exploring novel and innovative biomedical cancer treatment strategies, the integration of multiple functions on the small motor bodies is key to achieve further progress but remains unresolved. Here, we propose a dual-source powered Janus nanomotor whose composition integrates multiple photo-theranostic functions such as surface-enhanced Raman scattering (SERS) sensing, fluorescence imaging/photoacoustic imaging (PAI), photodynamic therapy (PDT), and photothermal therapy (PTT). This nanomotor can be fabricated by sputtering a thin gold layer onto one side of mesoporous silica (mSiO2) combined with surface modification by photo-sensitizer, Raman reporter, and catalase. Upon illumination with 808 nm near-infrared light, the half-coated gold nanoshell serves as PAI/PTT agent, and by upconverting NIR to visible light, the pre-loaded photosensitizer can be excited by the upconverted light of UCNPs to convert the dissolved oxygen (O2) into reactive oxygen species for efficient PDT. Furthermore, ratiometric SERS signal can be captured to quantitatively detect the tumor marker, H2O2, in cellular microenvironments. The immobilized catalase as a nano-engine can catalyze endogenous H2O2 to O2. This function not only improves the hypoxic tumor microenvironment and therefore enhances PDT efficiency, but also provides a thrust force for deep penetration. As a proof of concept for the in vivo trial we performed cancer photo-theranostics where our nanomotors successfully treated a mouse breast tumor in a subcutaneous tumor model. The results are promising and encourage the use of an integrated nanomotor platform that could be further developed into a photo-theranostic agent for superficial cancer treatment.

Comparative study of GaAs nanostructures synthesized in air and distilled water by picosecond pulsed laser ablation and application in hazardous molecules detection

This work explored the fundamental differences/mechanisms between the GaAs substrates ablated in two different media of air and distilled water (DW). A scan area of 5 × 5 mm2 was ablated by a picosecond laser with a pulse duration of 30 ps, a repetition rate of 10 Hz, a wavelength of 1064 nm, and a pulse energy of 2 mJ. The spacing between raster scan lines was varied (0.05–0.35 mm), keeping the scan speed (0.15 mm/s) constant. The obtained GaAs nanostructures (NSs) were thoroughly analyzed using microscopy techniques. A clear increase in separation between the raster scan lines was observed with an increase in the scan spacing for the GaAs NSs fabricated in air, whereas the same result was not observed in DW. Moreover, structures with debris were formed in air irrespective of the spacing, unlike the formation of uniform quasiperiodic GaAs NSs throughout the sample in the case of DW ablation. To the best of our knowledge, there are no reports on the detailed studies involving DW in the fabrication of quasiperiodic NSs of GaAs. Further, these quasiperiodic GaAs NSs formed in DW were coated with a thin layer of gold using the thermal evaporation method, annealed at 400 °C for 1 h in an ambient atmosphere. As a consequence of annealing, Au NPs were uniformly decorated on the quasiperiodic NSs of GaAs imparting plasmonic nature to the whole structures. Subsequently, the Au NPs decorated GaAs NSs were utilized as surface enhanced Raman scattering substrates for the detection of methylene blue (dye molecule) and Thiram (pesticide molecule) at low concentrations.

Resistivity dependence on nanostructure formation in picosecond ablation of silicon and SERS-based sensing applications

We report on the influence of resistivity in picosecond (ps) laser ablation of silicon (Si) leading to the formation of diverse surface micro- and nanostructures. Subsequently, we investigated their potential in sensing applications based on the surface enhanced Raman scattering (SERS) technique. The varying resistivity (ρ 1: 1–10 Ω cm, ρ 2: 0.01–0.02 Ω cm, ρ 3: 0.001–0.005 Ω cm) Si wafers were subjected to cross patterned ps laser ablation in ambient air. Ladder-like microstructures embedded with numerous nano growths were formed on low resistivity Si (ρ 3) while similar micro- and nanostructures were observed on higher resistivity Si (ρ 2 < ρ 1). The structures were non-plasmonic and anti-reflecting in nature with an optical reflectance of <6% over a broad range of wavelengths (350–1200 nm). Non-plasmonic Si microstructures were subsequently transformed to plasmonic by means of deposition of a thin layer of gold (Au). Additionally, the effect of annealing on the evolution of nanostructures was also investigated. We employed these hybrid substrates for the trace detection of an explosive molecule, ammonium nitrate, and dye, malachite green. Our detailed SERS studies have demonstrated a superior enhancement in the trace detection of analytes for low resistivity Si substrate. However, the annealed hybrid substrates have demonstrated further improvement in the SERS signal (by at least one order of magnitude). These detailed SERS investigations provide us a proof of the sensitivity of different resistivity Si nano/microstructures.

Plasmonically enhanced composite vortex beam generation using ultra-thin dielectric fork gratings

We experimentally demonstrate a simple method for the generation of composite vortex beams using resonant ultra-thin dielectric fork gratings (UFGs) of thicknesses an order of magnitude less than the incident wavelength. The degradation in the diffraction efficiency of these gratings at reduced dielectric thicknesses was computationally shown to be compensated for by introducing a thin continuous gold layer (Au, 30 nm) between the grating and the substrate. At the resonance wavelength, the diffraction efficiency of UFGs with Au was ∼ 4 times higher when compared to that of UFGs without Au, which was attributed to plasmon-induced transmission enhancement. UFGs were fabricated with optimized geometric parameters using electron beam lithography. These gratings showed lattice-plasmon resonance at the wavelength corresponding to the grating vector, resulting in vortex beams with a specific wavelength and polarization selectivity. Further, hybrid UFGs were designed by replacing a central concentric circular region of a UFG with another UFG of a different topological charge. These hybrid UFGs resulted in the formation of composite vortex beams, indicating that the relative spatial phase imparted to the lattice plasmon by hybrid gratings was preserved in the leaked radiation. These results can help in designing integrated, ultra-thin, low aspect ratio optical-phase-singularity structures for enhanced optical sources, detectors, and sensing applications.

Light‐Driven Shape Memory of 3D‐Printed PEEK for Programmable Actuations

AbstractRemotely controllable actuation of engineering polymers is highly demanded in the fast‐developing intelligent society. Here, this work demonstrates that the programmable shape memory of 3D‐printed poly(ether ether ketone) (PEEK), which is an excellent engineering material, could be driven by both ultraviolet (UV) light and natural sunlight. The shape recovery ratio reaches 97.6% and could be finely regulated by defining the sample thickness, shape programming, way of placement, and light intensity. Light‐induced continuous, sequential, and programed actuations (shape recovery) are further realized in various 3D‐printed PEEK structures. Meanwhile, the coating of a thin layer of gold is proven to be effective in anti‐UV oxidation and the enhancing of shape recovery. Moreover, natural sunlight during daytime is demonstrated to be able to induce the shape recovery of 3D‐printed PEEK in outdoor environment. The work here can pave the way for the use of PEEK as a smart material in the fields such as aerospace and intelligent industry.

Non-Destructive Scientific Analysis of the Gold Fabric Excavated of Cheongsong Shim’s Grave

Using non-destructive analytical methods, we identified the material characteristics of two gold fabric artifacts excavated from the Cheongsong Sim clan (Bugeum Wonsam, Jikgeum Chima), including the artifact condition, fiber type, surface contamination, and metallic threads. We found that the artifacts were buried and had turned brown; thus, we were unable to determine their original color. The fiber type was determined to be silk from cocoons, based on scanning electron microscopy, Fourier transform infrared (FT-IR) analyses of Amide I, II, III, and IV peaks, and color reactions Further, the FT-IR and X-ray fluorescence (XRF) analyses identified the white and black stains as natural resin hydrolyzed substances, such as lipids and proteins, that occurred as microbial decomposition due to body decay. Finally, the XRF analyses identified the thin gold layer of the metallic yarn as gold (Au). According to the FT-IR data and the color reaction to the metallic yarn medium, the adhesive component of the medium was a product of-Amides I, II, III, and 3000 cm-1 within Amides A and B (an animal type), respectively. Thus, the medium was identified as Hanji (Korean paper), which is made from domestically produced Broussonetia kazinoki fibers.

Dual polarized surface plasmon resonance refractive index sensor via decentering propagation-controlled core sensor

Refractive index (RI) is a unique attribute of bio-analytes which highly relies upon their concentrations or the activity/infectivity of the microbes. In this paper, a dual-polarized surface plasmon resonance (SPR) RI sensor based on a decentered propagation-controlled core photonic crystal fiber (PCF) has been studied. Fine-tuned light guidance is realized by scaling down the core air holes. The external surface of the fiber is metalized with a thin gold layer that maximizes the chemical stability by reducing the chances of oxidation. The deposition of the core from the central position reduces the core to analyte distance resulting in efficient coupling as well as greater sensitivity. Finite element method (FEM) based numerical investigation warrants promising sensing performances in wavelength and amplitude interrogation methods. The proposed sensor is viable for the RI range from 1.33 to 1.39, where it demonstrates the highest wavelength sensitivities of 13,700 and 15,400 nm/RIU and highest amplitude sensitivities of 852 RIU-1 and 654 RIU-1 in x-and y-polarized modes, respectively. It also exhibits high sensor resolutions of 7.30 × 10−6 RIU and 6.49 × 10−6 RIU, and high figure of merits of 216 and 256 RIU-1 for x and y-polarized modes, respectively. Along with the liberty of selecting light sources, the highly sensitive nature of the sensor will enable accurate detections of different organic compounds and bio-molecules.

Electrical conduction and noise spectroscopy of sodium-alginate gold-covered ultrathin films for flexible green electronics

Green electronics is an emerging topic that requires the exploration of new methodologies for the integration of green components into electronic devices. Therefore, the development of alternative and eco-friendly raw materials, biocompatible and biodegradable, is of great importance. Among these, sodium-alginate is a natural biopolymer extracted from marine algae having a great potential in terms of transparency, flexibility, and conductivity, when functionalized with a thin gold (Au) layer. The electrical transport of these flexible and conducting substrates has been studied, by DC measurements, from 300 to 10 K, to understand the interplay between the organic substrate and the metallic layer. The results were compared to reference bilayers based on polymethyl-methacrylate, a well-known polymer used in electronics. In addition, a detailed investigation of the electric noise properties was also performed. This analysis allows to study the effect of charge carriers fluctuations, providing important information to quantify the minimum metallic thickness required for electronic applications. In particular, the typical noise behavior of metallic compounds was observed in samples covered with 5 nm of Au, while noise levels related to a non-metallic conduction were found for a thickness of 4.5 nm, despite of the relatively good DC conductance of the bilayer.

Field enhancement in hydrogen storage by periodic layered structures

This paper investigates, through the field enhancement factor, the increase of hydrogen adsorption around the interface between a layer of hydrogen and a periodic layered structure under different incidence angles of an applied transverse magnetic polarized electromagnetic field. This periodic layered structure is composed of n-binary unit cells based on alternating a thin layer of gold with a thin layer of a metamaterial with equal negative relative permittivity while the relative permeability of the first and the second material's unit cell is considered equal to 1 and -1, respectively. We apply the effective medium theory to replace this layered structure with a single slab of a homogeneous material with an effective permittivity tensor and an effective permeability tensor. We use the Transfer Matrix Method to analyze the reflectivity spectra at the hydrogen/slab interface for adjustable layers’ thicknesses and then we derive the field enhancement factor. We obtain a significant increase of the field enhancement factor of the structure in comparison with the field enhancement factor around the interface between a layer of hydrogen and a structure composed of one gold layer.

Plasmonic sensor design using gold and silicon nitride waveguide at visible and NIR wavelengths

In this work, we present the modal analysis and the design consideration of a hybrid plasmonic waveguide (HPWG) based sensor. The device has a very simple structure and uses Silicon nitride (SiN) technology compatible with CMOS foundries, a top cladding of SiO2 and a thin gold layer. This noble metal is suitable for its stability, high sensitivity and its capability to propagate plasmons in the visible range. In order to obtain the best design, the article analyzes the behavior of the hybrid modes present in the structure for the visible and part of NIR spectrum region (400–1000 nm band), as well as the impact of oxide and gold on sensing performance. A compilation of the best potential cases with higher performances are presented from simulations based on 2D-FDTD solver. Sensitivities higher than 900 nm/RIU and FOM greater than 20 RIU−1 are reported. Finally, a discussion of our results and a roadmap to conduct similar designs are also presented.

Photonic Quasi-Crystal Fiber-Based Plasmonic Biosensor: a Platform for Detection of Coronavirus.

Since the coronavirus pandemic began, research groups worldwide developed diagnostic tests. One of the promising platforms for testing is an optical and plasmonic biosensor. Localized surface plasmon resonances owing to their highly concentrated field intensity provide highly sensitive devices. A beneficial approach to excite localized surface plasmon modes for field-based applications is using photonic crystal fibers while photonic quasi-crystals demonstrate a higher order of symmetry, the more isotropic Brillouin zone, and the easier achievement of photonic bandgap as compared with conventional photonic crystals. In this work, by exploiting a photonic quasi-crystal fiber, we are designing a surface plasmon resonance biosensor for the on-chip and real-time detection of coronaviruses. In our miniaturized design, a thin gold layer is employed on the outer layer of an air hole of a photonic quasi-crystal fiber with a 12-fold symmetry where the leakage of the fiber core mode can excite the surface plasmon resonance mode on the gold. According to three-dimensional finite-difference time-domain simulations, the proposed biosensor shows the sensitivity of 1172 nm/RIU in the detection of coronaviruses within the saliva. Moreover, the smallest detection limit obtained in the simulation is about 12 nm. These promising results altogether indicate that this reconfigurable and lab-on-a-chip platform can potentially be used in the detection of all kinds of coronaviruses.

High Sensitivity Surface Plasmon Resonance Sensor Based on a Ge-Doped Defect and D-Shaped Microstructured Optical Fiber.

In this work a plasmonic sensor with a D-Shaped microstructured optical fiber is proposed to detect a wide range of analyte refractive index by doping the pure silica core with distinct concentrations of Germanium Dioxide , causing the presentation of high spectral sensitivity. In this case, the fiber is shaped by polishing a coating of , on the region that will be doped with , in the polished area, a thin gold layer, which constitutes the plasmonic material, is introduced, followed by the analyte, in a way which the gold layer is deposited between the . and the analyte. The numerical results obtained in the study shows that the sensor can determine efficiently a range of 0.13 refractive index units , with a limit operation where varies from 1.32 to 1.45. Within this application, the sensor has reached an average wavelength sensitivity of up to . With this level of sensitivity, the D-Shaped format and wide range of detection, the proposed fiber has great potential for sensing applications in several areas.

High-Sensitive Detection and Quantitative Analysis of Thyroid-Stimulating Hormone Using Gold-Nanoshell-Based Lateral Flow Immunoassay Device.

Au nanoparticles (AuNPs) have been used as signal reporters in colorimetric lateral flow immunoassays (LFAs) for decades. However, it remains a major challenge to significantly improve the detection sensitivity of traditional LFAs due to the low brightness of AuNPs. As an alternative approach, we overcome this problem by utilizing 150 nm gold nanoshells (AuNSs) that were engineered by coating low-density silica nanoparticles with a thin layer of gold. AuNSs are dark green, have 14 times larger surface area, and are approximately 35 times brighter compared to AuNPs. In this study, we used detection of thyroid-stimulating hormone (TSH) in a proof-of-concept assay. The limit of detection (LOD) with AuNS-based LFA was 0.16 µIU/mL, which is 26 times more sensitive than the conventional colorimetric LFA that utilizes AuNP as a label. The dynamic range of the calibration curve was 0.16–9.5 µIU/mL, making it possible to diagnose both hyperthyroidism (<0.5 µIU/mL) and hypothyroidism (>5 µIU/mL) using AuNS-based LFA. Thus, the developed device has a strong potential for early screening and diagnosis of diseases related to the thyroid hormone.

Fabry–Pérot cavity resonance based metamaterial absorber for refractive index sensor at infrared frequencies

We present numerical studies on a simple metamaterial absorber design operating at near-infrared frequencies. The absorber consists of a one-dimensional silicon strip array on a silicon substrate followed by a thin layer of gold with a thickness of 30 nm. Computer Simulation Technology Microwave Studio (CST Microwave Studio) based on finite integration technique was used for numerical simulations and to understand the mechanism of absorption in the system. Simulation results show that the absorber has an absorptance of around 0.99 with a full width at half-maximum (FWHM) of 18 nm. The absorption is caused by the simultaneous excitation of Fabry–Pérot (FP) cavity resonance in the strip and between the consecutive strips, which leads to the confinement of electric fields in the strip and between the strips. In addition, we have also analyzed the sensing performance of the absorber in refractive index (RI) and found that it has high sensitivity and a large figure of merit (FOM). Therefore, the absorber can be exploited for high-performance RI sensor for sensing chemicals and biological samples, and even acidic samples due to its component’s wise robustness.