Ag Nanoarrays Research Articles

Fabricating periodic sandwich SERS structure in detecting SARS-CoV-2 S protein with high-performance

This study reported a sandwich SERS structure in detecting SARS-CoV-2 spike protein (SARS-CoV-2 S protein) with high performance. The periodic Ag nanoarrays (AgNAs) functionalized with angiotensin-converting enzyme 2 (ACE2) were utilized as the bottom structure to specifically bound to the SARS-CoV-2 S protein. A complex of SARS-CoV-2 S protein antibody and 4-mercaptobenzoic acid (4-Mba) modified Au nanoparticles (AuNPs@4-Mba@Antibody) were used as nanotags and top SERS enhancing structures. By utilized the “hot spots” in parallel and perpendicular directions, the SERS signals of the 4-Mba as reporters were largely enhanced. By modulated the diameters and the heights of the AgNAs, the SERS performance of the sandwich structures was optimized by using R6G as a stand analyst with limits of detection (LOD) of 1 × 10−9 M. By applied the optimized sandwich structures in detecting SARS-CoV-2 S protein in phosphate buffered saline (PBS) and pharyngeal swabs solution (PSS), the proposed sandwich structure illustrates a high performance, and the LODs were 0.1 fg mL−1 and 1 fg mL−1, respectively. This study presented an efficient way to construct a sandwich SERS structure in directly detecting SARS-CoV-2 S protein and this method illustrates a good potential in viral detection.

Highly flexible copper tape decorated with Ag nanoarrays as ultrasensitive SERS platforms for multi-hazardous pollutant sensing.

Ahighly flexible and cost-effective copper tape decorated with silver nanoparticles (Cu-TAg) has been developed for surface-enhanced Raman spectroscopy (SERS) sensing of multi-hazardous environmental pollutants. Highly ordered and spherical-shaped silver nanoarrays have been fabricated using a low-cost thermal evaporation method. The structural, morphological, and optical properties of Cu-TAg sensors have been studied and correlated to the corresponding SERS performances. The size of nanoparticles has been successively tuned by varying the deposition time from 5 to 25s. The nanoparticle sizes were enhanced with an increase in the evaporation time. SERS investigations have revealed that the sensing potential is subsequently improved with an increase in deposition time up to 10s and then deteriorates with further increase in Ag deposition. The highest SERS activity was acquired for an optimum size of ~ 37nm; further simulation studies confirmed this observation. Moreover, Cu-TAg sensors exhibited high sensitivity, reproducibility, and recycling characteristics to be used as excellent chemo-sensors. The lower detection limit estimation revealed that it can sense even in the pico-molar range for sensing of rhodamine 6G and methylene blue. The estimated enhancement factor of the sensor is found to be 9.4 × 107. Molecular-specific sensing of a wide range of pollutants such as rhodamine 6G, alizarin red, methylene blue, butylated hydroxy anisole, and penicillin-streptomycin is demonstrated with high efficiencies for micromolar spiked samples. Copper tape functionalized with Ag arrays thus demonstrated to be a promising candidate for low-cost and reusable chemo-sensors for environmental remediation applications.

Highly efficient, multiplexed SERS sensing of para-aminobenzoic acid using reusable silver nanoarrays for environmental monitoring

Highly effective optical sensors can act as next-generation chemo-sensors, which can facilitate fast sensing with superior sensitivity, reproducibility and reusability characteristics. Here, we investigated the feasibility of thermally evaporated Ag nanoarrays as cost-effective and reusable substrates for multiplexed para-aminobenzoic acid (PABA) sensing for environmental remediation applications. SERS performances of Ag/Si sensors were investigated as a function of the thickness. The thickness of Ag nanoarrays was increased with evaporation time and a thickness of ∼18 nm exhibited the highest SERS enhancement. Ag nanoarrays with narrower size distribution on Si exhibited three-fold SERS enhancement than Ag/glass. Simulation studies revealed 70 times higher enhancement in the electromagnetic field in Ag/Si than in Ag/Glass. Ag/Si sensor possesses high efficiency, reproducibility, excellent recyclability and a low detection limit near femtomolar levels for sensing PABA. Moreover, the developed sensor established multiplexed detection of PABA and R6G; demonstrated to be an excellent chemo-sensors for environmental applications.

Resonance-enhanced second harmonic generation via quantum dots integrated with Ag nanoarrays

The metal nanoarray can couple the excitation light energy to the surface, resulting in local electromagnetic field enhancement due to the resonance effect. This is beneficial to the generation of nonlinear optical processes which depend on electromagnetic resonance enhancement, taking advantage of the field enhancement properties of metal nanoarray. Here, silver nanoperiodic arrays are integrated with AgInS2 quantum dots (QDs) to enhance the second harmonic generation (SHG) process of QDs. The experimental results show that the enhancement factor of SHG is 8.8-fold in the condition of surface plasmon resonance. In contrast, the second harmonic emission from pure quantum dots is very weak. The simulation reveals that the second harmonic enhancement is caused by the resonance between the incident laser and the Ag nanoarray. The experimental results show that it is feasible to generate a highly efficient nonlinear optical process of QDs assisted by metal nanoarray. This is beneficial for extending the nonlinear applications of quantum dots.

Synthesis of carboxylic acid-functionalized polymethacrylate-b-polystyrene as an Ag ion-loadable block copolymer thin film template

We report the synthesis of thiopropionic acid-functionalized polymethacrylate-b-polystyrene (PMATA-b-PS) as a template for patterning Ag nanoarrays. Reversible addition-fragmentation chain transfer (RAFT) polymerization of silyl-protected propagyl methacrylate followed by chain extension with styrene produced a block copolymer precursor. Deprotection of the trimethylsilyl group and subsequent thiol-yne reaction afforded the target, PMATA-b-PS. While the entire series of the precursor was in the disordered phase, microphase separated morphologies were identified from PMATA-b-PS, indicating an increased interaction parameter (χ) as a result of introducing the acid groups. As a preliminary result, we show that an Ag nanoparticle array can be fabricated by selectively associating Ag+ ions to the PMATA cylinders in the thin film of PMATA-b-PS and removing the organic polymer layer by oxygen plasma treatment.

Toward highly sensitive surface-enhanced Raman scattering: the design of a 3D hybrid system with monolayer graphene sandwiched between silver nanohole arrays and gold nanoparticles.

We report a novel graphene-metal hybrid system by introducing monolayer graphene between gold nanoparticles (Au NPs) and silver nanohole (Ag NH) arrays. The design incorporates three key advantages to promote the surface-enhanced Raman scattering (SERS) sensing capacity: (i) making full use of the single-atomic feature of graphene for generating uniform sub-nanometer spaces; (ii) maintaining the bottom layer of Ag nanoarrays with an ordered manner for facilitating the transfer of graphene films and assembly of the top layer of Au NPs; (iii) integrating the advantages of the strong plasmonic effect of Ag, the chemical stability of Au, as well as the mechanical flexibility and biological compatibility of graphene. In this configuration, the plasmonic properties can be fine-tuned by separately optimizing the horizontal or vertical gaps between the metal NPs. Exactly, sub-20 nm spaces between the horizontally patterned Ag tips constructed by adjacent Ag NHs, and sub-nanometer scale graphene gaps between the vertically distributed Au NP-Ag NH have been achieved. Finite element numerical simulations demonstrate that the multi-dimensional plasmonic couplings (including the Au NP-Au NP, Au NP-Ag NH and Ag NH-Ag NH couplings) promote for the hybrid platform an electric field enhancement up to 137 times. Impressively, the as-prepared 3D Au NP-graphene-Ag NH array hybrid structure manifests ultrahigh SERS sensitivity with a detection limit of 10-13 M for R6G molecules, as well as good reproducibility and stability. This work represents a step towards high-performance SERS substrate fabrication, and opens up a new route for graphene-plasmonic hybrids in SERS applications.

Comparative investigation on designs of light absorption enhancement of ultrathin crystalline silicon for photovoltaic applications

Ultrathin crystalline silicon wafers for photovoltaic applications have attracted intensive attention because of potential benefits in cost-effectiveness. Structural design with high light absorption is important for photovoltaics because planar ultrathin silicon is poor in absorption. We conduct a comparative investigation on designs of light absorption enhancement for 2-μm-thick ultrathin crystalline silicon, where the front texture is a nanopyramidal structure and the rear adopts several designs. Our calculation results show that both of the ultrathin silicon with front nanopyramids and rear silver nanoarrays and the ultrathin silicon with two-sided nanopyramids are promising for photovoltaic applications. For the latter design, the calculated photocurrent achieves the highest value of 35.1 mA/cm2 when a perfect electric conductor layer is applied at the bottom. In contrast, the former design has a lower photocurrent value of 31.2 mA/cm2. But, this design is of practical significance because the majority of experimental reports on ultrathin crystalline silicon solar cells are single-sided front-textured at present and the fabrication techniques of plasmonic Ag nanoarrays are matured. Compared with previous reports, the present work offers a multiple option of structural designs for ultrathin crystalline silicon to enhance the light absorption for photovoltaic applications.

Simulation of localized surface plasmon resonance of hexagonal Ag nanoarrays and amorphous oxidized silicon nitride

Simulation on the properties of localized surface plasmon resonance (LSPR) of different sized hexagonal Ag nanoarrays embedded in the amorphous oxidized silicon nitride(a-SiNx:O) matrix has been carried out by using COMSOL Multiphysics and FDTD Solution simulation software. Through the calculation of the scattering and absorption cross section of Ag array with different radius, we find that the position of extinction peaks red-shift from 460 to 630 nm when the radius of nanoparticles of hexagonal Ag arrays increases from 25 to 100 nm with the distance between particles 100 nm. The enhanced scattering cross section of the localized surface plasmon (LSP) and blue-shift of the extinction peak can be obtained by tunning the distance between Ag nanoparticles from 100 to 50 nm with the radius of Ag nanoparticles fixed at 50 and 75 nm, respectively. However the mismatch between the extinction peak of hexagonal Ag nanoarrays and the blue light emission of 460 nm from a-SiNx:O films still exists. The novel overlap between the scattering cross section of LSP from hexagonal Ag arrays with a radius of 25 nm and the blue light emission of a-SiNx:O films at 460 nm further confirms that the hexagnoal Ag arrays with a radius of 25 nm is the optimal option to enhance the blue light emission from a-SiNx:O films. Therefore, strong coupling between LSP and blue light emission at 460 nm from a-SiNx:O films with a thickness of 70 nm can be realized when the radius of Ag nanoparticle is 25 nm. We also investigate the enhancement of near field radiative intensity of LSP from hexagnoal Ag arrays with a radius of 25 nm. When the excitation wavelength is 460 nm, the maximum enhancement of near field intensity of LSP from hexagnoal Ag arrays with a radius of 25 nm reaches 1.46104 V/m. The calculated polarization intensity and charge distribution of hexagonal Ag nanoparticle with a radius of 25 nm embedded in a-SiNx:O films reveal that the enhancement of electromagnetic field-intensity is through the dipolar plasmon coupling with the excitons in a-SiNx:O films in bright field mode under the excitation of 460 nm. Further calculation of perpendicular radiative intensity for LSP from the hexagonal Ag array with a radius of 25 nm embedded in a-SiNx:O films indicates that the maximum radiative intensity can be realized in a-SiNx:O matrix with an optimum thickness of 30 nm for a-SiNx:O films. Our theoretical calculations and analysis can provide valuable reference for the design of Si-base blue LED with light emission around 460 nm.

Hexagonal Ag nanoarrays induced enhancement of blue light emission from amorphous oxidized silicon nitride via localized surface plasmon coupling.

A significant enhancement of blue light emission from amorphous oxidized silicon nitride (a-SiNx:O) films is achieved by introduction of ordered and size-controllable arrays of Ag nanoparticles between the silicon substrate and a-SiNx:O films. Using hexagonal arrays of Ag nanoparticles fabricated by nanosphere lithography, the localized surface plasmons (LSPs) resonance can effectively increase the internal quantum efficiency from 3.9% to 13.3%. Theoretical calculation confirms that the electromagnetic field-intensity enhancement is through the dipole surface plasma coupling with the excitons of a-SiNx:O films, which demonstrates a-SiNx:O films with enhanced blue emission are promising for silicon-based light-emitting applications by patterned Ag arrays.

Templated deposition of multiscale periodic metallic nanodot arrays with sub-10 nm gaps on rigid and flexible substrates

Multiscale metallic nanostrucutures, which support hybrid coupling of plasmon resonances, are essential for the engineering of plasmonic devices. The fabrication of large area periodic multiscale structures still remains a challenge, considering the cost and efficiency. In this work, highly ordered multiscale Ag nanoarrays with lateral dimensions of up to 6 mm × 6 mm have been successfully fabricated on both rigid silicon and flexible polydimethylsiloxane (PDMS) substrate by thermal evaporation using ultrathin anodic aluminum oxide films as masks. Owing to the peculiarities of thermal evaporation and the variance of substrate surface energy, the unit cell of the periodic arrays consist of a core-satellite structure on silicon and randomly distributed child particles on PDMS, with gaps as small as 10 nm. The flexible Ag nanoarrays on PDMS demonstrate a broadband extraordinary optical transmission with an enhancement up to 2.7 times when normalized to the exposed area. Moreover, the transmission and diffraction properties can readily be controlled by stretching the PDMS. These tunable optical properties support the multiscale Ag nanoarrays to be applied in some optical and optoelectronic devices.

Bilayer hybrid nanoimprinting method for fabricating embedded silver nanostructure arrays with enhanced photoluminescence

A bilayer hybrid nanoimprinting (NI) method was developed for fabricating embedded metal nanopatterns with greater processability and improved reliability for enhanced photoluminescence (PL) in optoelectronic devices. Bilayer hybrid NI consists of the following: (a) spin-coating ultraviolet (UV) and thermally curable NI resists in sequence, (b) high-pressure thermal NI and UV exposure while maintaining the stamp in a pressed position, and (c) silver (Ag) deposition and lift-off using a thermal NI resist on the upper surface to create embedded Ag nanoarrays. Reference samples with no Ag nanopatterns and with protruding Ag dot-shaped nanopatterns were also fabricated for comparison. The transmittance and PL of all samples were measured. All samples containing Ag nanopatterns exhibited improved PL compared with reference samples with no Ag. For all pattern sizes, the samples with the embedded Ag nanoarrays exhibited the highest PL; the relative PL enhancements compared with samples with Ag dot-shaped nanoarrays were 32.2%, 36.1%, and 62.7% for pattern sizes of 150, 200, and 265 nm, respectively. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10.1117/1.JNP.8.083089)

Comparative study of light absorption enhancement in ultrathin a-Si:H solar cells with conformal parabolaconical nanoarrays

Light trapping design is of critical importance for ultrathin a-Si:H solar cells. Three modelling methods are adopted for the amorphous silicon layer. The best modelling method is identified to achieve high-quality simulation results. Then, parabolaconical nanoarrays are introduced into ultrathin a-Si:H solar cells to study the design principle of high light absorption. Because a trade-off factor is often involved in solar cell consideration, light absorption is investigated for ultrathin a-Si:H solar cells with four conformal nanostructures, where a parabolaconical Ag nanoarray and a parabolaconical Al:ZnO nanoarray are included, respectively. Meanwhile, two height/radius ratios of 1 and 3 are considered, respectively. As a result, three promising structures and their respective optimal parameters are obtained. When the height/radius ratio is 1, the optimal absorption enhancement is 53.9% for a-Si:H solar cells with conformal parabolaconical Ag nanoarrays at a radius of 120 nm. When the height/radius ratio becomes 3, the optimal absorption enhancement is increased to 61.9% at a radius of 50 nm. Under the ratio of 3, it is found that the light absorption enhancement is 65.0% for the solar cells with conformal Al:ZnO nanoarrays. These design principles can provide an effective guide for the research and development of low-cost ultrathin a-Si:H solar cells.

TiO<sub>2</sub> Thin Layer Coated Ag Nanoarrays Complex for Surface-Enhanced Raman Scattering Substrate

A novel method to prepare TiO2-coated Ag nanowire arrays for use as surface enhanced Raman scattering (SERS) active substrate is studied. First, Ag nanowires with an average diameter of 60 nm and length of several μm were synthesized in an anodic aluminum oxide (AAO) template by direct electrodeposition into the template. Then TiO2thin layers with a 20 nm thickness were coated on Ag nanoarrays in large scale by a hydrolysis approach of tetrabutyl titanate. The SERS substrates prepared by this strategy have been proved as excellent candidates for the detection of organic pollutants by enhancing the SERS signals of these target species. The detection limit of methyl-parathion (MP) can be reduced to 10-6M.

Effects of thermal evaporation and electron beam evaporation on two-dimensional patterned Ag nanostructure during nanosphere lithography

In the process of fabricating two-dimensional Ag nano-arrays via nanosphere lithography, different deposition methods present different lattice point shapes of Ag nanostructure. Nano-triangles are produced by thermal evaporation whereas nano-rings are obtained by electron beam evaporation although they are both of hexagonal lattice. It is indicated that the sizes, the surface nanocurvature, the thermal and the kinetic energies of the particles deposited are key factors controlling the formation of the shape of Ag lattice point.

Self-Organization of Ordered Silver Nanocrystal Arrays on Cubic Mesoporous Silica Surfaces

Regular and oriented silver nanocrystalline arrays loaded on the surface of cubic mesoporous silica MCM-48 material was obtained by an approach of impregnation followed by thermal treatment. The self-assembly of Ag clusters at a suitable temperature influenced by the periodic surface stress field of the ordered mesopore structures is believed to lead to the ordered Ag nanoarrays.