Ag Nanorods Research Articles

Au-Cu-M (M = Pt, Pd, Ag) nanorods with enhanced catalytic efficiency by galvanic replacement reaction.

This work reports a general wet-chemistry method to produce Au-Cu-X (X = Pt, Pd, and Ag) trimetallic nanorods using galvanic replacement reaction with Au-Cu nanorods as the templates. The mild conditions, such as low temperature and slow injection of metal precursors, contributed to the slow galvanic replacement reaction and helped keep the rod structure intact. The distribution of Au, Cu and the doping metals was even in the rods as confirmed by elemental mapping. The alloyed trimetallic nanorods showed enhanced catalytic activity for p-nitrophenol reduction after incorporating the third metal. Remarkably, the Au-Cu-Pd and Au-Cu-Pt nanorods show more than an order of magnitude improvement in the mass activities compared to the Au-Cu nanorods. This facile and general synthetic method can be applied to fabricate other multimetallic nanoparticles with varying shapes and compositions.

Hydrophobicity of Highly Ordered Nanorod Polycrystalline Nickel and Silver Surfaces

Highly ordered nickel and silver nanorods arrays prepared by alumina template assisted electrodeposition were investigated to determine the effect of the array geometry on metal surface hydrophobicity and adhesion forces. The nanorod geometry, clustering and pinning were used to characterize surface hydrophobicity and its modulation. A contribution of metal crystallographic orientation to the surface energy was calculated. To characterize nanorod array surface properties and elucidate the source of the particle adhesion effects has been calculated. The dispersive components of surface tension γSD and surface polarizability ks, as surface features that markedly characterize hydrophobicity and adhesion, were calculated. The highest hydrophobicity was found for Ag nanorods with aspect ratio of 10 then Ni nanorods with aspect ratio 10. The same geometry of nanorods particles resulted in different surface hydrophobicity and it was ascribed to the orientation of Ag and Ni crystals formed on the top of nanorods. Due to high hydrophobicity nanorod array surfaces could be used as an antifouling surface in medicine to select areas on implant surface not to be colonized by cells and tissues.

Standing wave type localized surface plasmon resonance of multifold Ag nanorods

Multifold Ag nanorods (AgNRs) have demonstrated great potentials in applications such as surface-enhanced Raman scattering technique due to their specially organized nanostructures. However, there is so far no systematic understanding of their localized surface plasmon resonance (LSPR) behaviors. This work comprehensively studied the plasmonic behaviors of AgNRs with 1, 2 and 3 folded arms. LSPR modes with charge oscillations resembling standing waves were excited in all nanostructures. As arm length increases, there were linear relationships between resonance wavelength and arm length, which applied to all LSPR modes studied. In addition, directly proportional relationships between the slopes of the linear functions and arm number were found for same order LSPR modes of AgNRs. For different modes of a specific AgNR, inversely proportional relationships between the slope and the resonance order N were discovered. These findings evidenced AgNR’s standing wave type LSPR characteristics.

Facile and sensitive S1 endonuclease activity and inhibition assay using positively-charged Ag nanorods

In this work, we designed a facile and promising strategy for fluorescence determination of S1 endonuclease activity and inhibition based on fluorescence resonance energy transfer (FRET) between positively Ag nanorods (AgNRs) and negatively-charged ROX-labeled sing-stranded DNA (ROX-ssDNA). In the absence of S1 endonuclease, the fluorescence signal of the ROX-ssDNA was efficiently quenched when the ROX-ssDNA was adsorbed on the surface of AgNRs via strong electrostatic interaction. However, upon addition of different concentration of S1 endonuclease, the fluorescence was gradually restored owing to the reduction of FRET efficiency caused by S1 endonuclease specific cleavage ROX-ssDNA into short fragments, which reduced the electrostatic interaction between AgNRs and short oligonucleotide fragment. This assay strategy exhibited a high sensitivity and excellent specificity for S1 endonuclease with a detection limit of 0.004 U/mL and a dynamic concentration range from 0.01 U/mL to 5.0 U/mL. In addition, the capabilities for screening of S1 endonuclease inhibitors and S1 endonuclease detection from complex biological matrixes were also verified.

Smartphone based dual mode in situ detection of viability of bacteria using Ag nanorods array

The in-situ and rapid detection of live and dead bacteria is essential for human and environmental care. It has become one of the biggest needs in the biological and medical sciences to prevent infectious diseases, which usually occur in hospitals and field clinics. In the current scenario, antibiotic resistance is one of the severe public health problems, which requires a quick and efficient solution. Here, we report a facile sensitive, portable, user-friendly, cost-effective and time saving approach for detection of live, dead and drug-resistant bacteria. The endogenous H2S evolution was targeted to differentiate between live and dead as well as antibiotic resistant bacteria. The silver nanorods (AgNRs) arrays sensors were fabricated by glancing angle deposition technique. The colorimetric and water wettability features of as-synthesized AgNRs are found to be highly sensitive and selective for H2S. E. coli. P. aeruginosa, B. subtilis and S. aureus were used as a model organism in this study. All the bacteria were found to produce H2S by their metabolism process. In order to detect the antibiotic resistant E. coli were grown in the presence of different concentration of ampicillin in Luria broth. A drastic visible change in color as well as wetting of AgNRs array was observed. To make the technique easy, a user-friendly and field deployable mobile app ‘Colorimetric Detector’ was developed. This technique takes only 4–6 h whereas the conventional methods need around 24 h for the same. This dual mode facile and, inexpensive method can be easily scaled up in the field of diagnostics.

Development of a Protein Microarray Chip with Enhanced Fluorescence for Identification of Semen and Vaginal Fluid.

The detection of body fluids has been used to identify a suspect and build a criminal case. As the amount of evidence collected at a crime site is limited, a multiplex identification system for body fluids using a small amount of sample is required. In this study, we proposed a multiplex detection platform using an Ag vertical nanorod metal enhanced fluorescence (MEF) substrate for semen and vaginal fluid (VF), which are important evidence in cases of sexual crime. The Ag nanorod MEF substrate with a length of 500 nm was fabricated by glancing angle deposition, and amino functionalization was conducted to improve binding ability. The effect of incubation time was analyzed, and an incubation time of 60 min was selected, at which the fluorescence signal was saturated. To assess the performance of the developed identification chip, the identification of semen and VF was carried out. The developed sensor could selectively identify semen and VF without any cross-reactivity. The limit of detection of the fabricated microarray chip was 10 times better than the commercially available rapid stain identification (RSID) Semen kit.

Highly ordered Au-decorated Ag nanorod arrays as an ultrasensitive and reusable substrate for surface enhanced Raman scattering

For surface-enhanced Raman spectroscopy (SERS) substrates, complexity of the fabrication process, sensitivity and stability are factors that need to be considered. We report a simple and novel method for preparing an effective substrate that greatly enhances SERS signals. The SERS substrate is fabricated by selectively electroless deposition of Ag nanoparticles in the highly ordered porous anodized aluminum oxide (AAO) template and then etching it to form Ag nanorod bundles structure, so that the Raman enhancement occurs in the gap between the nanorods and the top of the nanorod bundle, which is verified by finite element analysis. A peculiarity of this method is that this is the first time to synthesize Ag nanorod arrays structure by using it. The results indicated that this prepared substrate has special micro-nano structure and when rhodamine 6 G is selected as the detection reagent, the detection limit is as low as 10−16 M with excellent recyclability. This outstanding array structure has a promising practical application in SERS field.

NIR-Active Plasmonic Gold Nanocapsules Synthesized Using Thermally Induced Seed Twinning for Surface-Enhanced Raman Scattering Applications.

Hollow and porous core-shell nanostructures with defined interior nanogaps are of great significance in the field of surface-enhanced Raman scattering (SERS) applications because of the presence of intrinsic electromagnetic (EM) hot spots, multipolar resonances, and multiple facets. Further, nanomaterials having extinction in the near-infrared (NIR) region are particularly important for SERS and biomedical applications, and thus it is highly desirable to synthesize NIR-active plasmonic nanostructures. Herein, we report the synthesis of gold nanocapsules having a solid Au bead as core and a thin-porous rod-shaped shell with extinction in both NIR I and NIR II regions. Thermally induced twinned seeds were used for the silver-free synthesis of pentatwinned Au bead, which served as the foundation for the directed growth of Ag nanorods, which was finally converted to Au nanocapsules following galvanic replacement reaction (GRR). Detailed investigation was carried out to understand the effect of thermal treatment duration in the seed morphology and its subsequent growth to anisotropic Au beads. Ag overgrowth on Au beads yielded uniform Au-bead@Ag nanorods whose size can be tuned by varying the Ag precursor. Five different sized Au-bead@Ag nanorods were studied, and they were converted to Au nanocapsules following GRR. We explored the size-dependent SERS activity of the prepared Au nanocapsules along with their comparison with solid pentatwinned Au beads and found that the smallest sized Au nanocapsules were the best SERS performers. Finite-difference time-domain simulation revealed the presence of intense EM hot spots in the smallest sized Au nanocapsule and corroborated the experimental SERS data. Finally, we fabricated a simple flexible cellulose-based SERS substrate by using the smallest sized Au nanocapsules and investigated its SERS sensing ability for the detection of 2-napthalenethiol (2-NT), as a model analyte, and were able to achieve its detection down to 1 fM concentration.

Promotion of Ternary Pt–Sn–Ag Catalysts toward Ethanol Oxidation Reaction: Revealing Electronic and Structural Effects of Additive Metals

The use of a computation-guided method and the discovered structure–property relationship would establish a rational strategy to aid the development of ethanol oxidation reaction (EOR) catalysts for possible commercialization of direct ethanol fuel cells. Here, we investigate the promotion roles of additive metals in ternary Pt–Sn–Ag catalysts toward EOR via a combination of density functional theory calculation and experimental evidence. By calculating the EOR energetics, the promotion roles of Sn and Ag were revealed from the viewpoints of electronic and structural effects, respectively: (1) The addition of Sn and Ag on Pt essentially reduce the reaction energy and activation barrier of the second two-electron transfer process of EOR, facilitating the oxidation of acetaldehyde to acetic acid; (2) a homogeneous Pt–Sn–Ag surface configuration strengthens the adsorption energy of ethanol, thus improving the activity for ethanol oxidizing to acetaldehyde. Experimentally, various Pt–Sn–Ag nanorod catalysts ...

Effective Radiative Properties of Tilted Metallic Nanorod Arrays Considering Polarization Coupling

With the advent of new nanomanufacturing techniques has come the rise of the field of nanophotonics and an increased need to determine optical properties of novel structures. Commercial software packages are able to estimate the behavior, but require large resources and heavy computational time. By combining coordinate transforms and Effective Medium Theory (EMT), an effective relative permittivity tensor is defined and further exploited to calculate the polarization-coupled Fresnel coefficients through Maxwell’s equations. A uniaxial simplification is made to show the case of tilted nanorod arrays. To demonstrate the flexibility of this system, the interfacial reflectance has been calculated for both s- and p-polarizations as well as the coupled case with the volume filling fractions of f = 0.10 and 0.30 for silver (Ag) and titanium (Ti) nanorods, and a scenario of a Ag nanorod array with polymethyl methacrylate (PMMA) as the surrounding medium. The exact results computed by the finite-difference time-domain method justify the validity of EMT with polarization coupling taken into account. The effects of incidence angle and azimuthal angle on reflectance are also discussed. The relatively simple nature of this approach allows for fast estimations of the optical properties of various nanostructures.

Spectral Tuning of Plasmonic Absorption for High-Transmittance Nanostructured Metal Electrodes

Networks of metal nanostructures are considered promising candidates for next-generation transparent electrodes. However, localized surface plasmon-mediated absorption at specific visible wavelengths limits their extensive use in a diverse range of photonic applications. This study proposes a strategy that spectrally tunes plasmonic absorption modes within periodic metal nanostructures with the aim of obtaining high-transmittance, transparent electrodes. A theoretical analysis of the periodic Ag nanostructures identifies localized surface plasmon resonances that have asymmetric (i.e., air-concentrated or substrate-concentrated) energy distributions due to the underlying substrate. The wavelength of a substrate-concentrated mode can be readily shifted by using a rationally designed dielectric spacer, which is leveraged to avoid plasmonic absorption at target wavelengths. A scattering analysis of a single Ag nanorod qualitatively supports the spectral tuning of plasmonic absorption modes. These theoretical findings will provide useful information for designing metal nanostructures for general transmission or absorption devices.

Ultra-sensitive room-temperature H2S sensor using Ag–In2O3 nanorod composites

Ultra-sensitive H2S sensors operated at room temperature were fabricated using Ag–In2O3 nanorod composites synthesized using sol–hydrothermal method followed by NaBH4 reduction process. TEM proved that the In2O3 was nanorod structures of ~ 110 nm in length and ~ 35 nm in diameter. Ag nanoparticles with diameters from 10 to 15 nm homogeneously decorated on the surfaces of the In2O3 naonorods. XRD and XPS analysis proved that the Ag elements existed as zero-valent metallic silver on the surface of the In2O3 nanorods. Ag nanoparticles could enhance the formation of chemisorbed oxygen species and interactions between H2S molecules and oxygen species due to spillover effect, and the electron transfer between Ag and In2O3 nanorods also enhanced the sensing properties. Therefore, the H2S sensors based on the Ag–In2O3 nanorod composites showed significantly improved sensing performance than those based on the pure In2O3 nanorods. The optimized content of Ag nanoparticles is 13.6 wt%. Operated at room temperature, the H2S sensors made of 13.6 wt% Ag–In2O3 nanorod composites exhibited an ultra-high response of 93719 to 20 ppm H2S and a superior detection limit of 0.005 ppm. The sensor also showed good reversibility, good selectivity, excellent reproducibility and stability for detection of H2S gas.

Zigzag Localized Surface Plasmon Resonance Wavelength Shift of Asymmetric V-Shape Ag Nanorods

Asymmetry could significantly affect a nanoparticle’s localized surface plasmon resonance (LSPR) behaviors, although limited attention has been drawn on this fascinating phenomenon. In this work, asymmetry’s influence on the LSPR behaviors of V-shape Ag nanorods was systematically studied. The introduction of asymmetry generated a zigzag resonance wavelength shift pattern with alternative blue and red shifts. In the zigzag patterns, the number of bends proportionally increased with the order of resonance mode: from the first to the fifth mode, the patterns showed 0 to 4 bends, respectively. Moreover, wavelength extremums were always reached at certain asymmetry degrees of k/n, where n is the resonance order number and k is any integer from 1 to n – 1. Detailed explanations contributing to these phenomena were discussed at last, which might relate to the variation of pole distance and the corresponding energy fluctuation as the asymmetry degree changed.

Depolying Tunable Metal-Shell/Dielectric Core Nanorod Arrays as the Virtually Perfect Absorber in the Near-Infrared Regime.

In this paper, the coupled Ag-shell/dielectric-core nanorod for sensor application is investigated and the different dielectric core plasmonic metamaterial is adopted in our design. The operational principle is based on the concept of combining the lattice resonance, localized surface plasmon resonance (SPR), and cavity plasmon resonance modes within the nanostructure. The underlying mechanisms are investigated numerically by using the three-dimensional finite element method and the numerical results of coupled solid Ag nanorods are included for comparison. The characteristic absorptance/reflectance peaks/dips have been demonstrated to be induced by different plasmonic modes that could lead to different responses required for plasmonic sensors. A nearly perfect absorptance and an approximate zero reflectance with a sharp band linewidth are obtained from the proposed system, when operated as an SPR sensor with the sensitivity and figure of merit of 757.58 nm/RIU (RIU is the refractive index unit) and 50.51 (RIU–1), respectively. Our work provides a promising method for the future developments of more advanced metamaterial absorber for chemical sensing, thermal radiation tailoring, field enhanced spectroscopy, and general filtering applications.

Plasmonic effects in composite metal nanostructures for sensing applications

We have investigated numerically the plasmonic effect on a two-dimensional periodic array of metallic nanostructures. The unit cell of the array has an Ag nanosphere and nanorod pair formed in a single structure. Three-dimensional finite element method is used for the study on the sensing performance within the optical spectra. The study takes into account the influences of the structural and material parameters, the rotational angle of the metal nanostructure, the number of metal nanostructure per unit cell, and the localized surface plasmon resonances. The proposed nanostructures function as a refractive index sensor with a sensitivity of 400 nm/RIU (RIU is the refractive index unit), showing the characteristics of low transmittance (T = 3.90%), high absorptance (A = 94.5%), and near-zero reflectance (R = 0.15%), could be achieved by a triangular arrangement of nanostructures within a unit cell. We also show how the tailoring of the structural parameters relates to the specific sensing schematics of the sensor.

Enhancement in energy storage density of polyvinylidene fluoride composites by introduced rod-like core-shell Ag@Al2O3 nanorods

A typical core-shell structural silver@aluminum oxide (Ag@Al2O3) nanorods was successfully synthesized by silver nitrate reduction method combined with hydrolysis of aluminum sulfate. The Ag@Al2O3 core-shell nanorods were used as functional fillers to improve the dielectric properties of polyvinylidene fluoride (PVDF). The thermal, mechanical and dielectrical properties of PVDF based composites were characterized. A comparative study on the dielectric properties of PVDF based composites with the filler of Ag and Ag@Al2O3 core-shell nanorods was also reported. Results showed that Al2O3 could make a homogeneous shell out of the Ag nanorods, and the Ag@Al2O3 core-shell nanorods also have a good dispersion in PVDF matrix. The Ag@Al2O3/PVDF composites with 15 wt% have a more superior expression on energy density (0.026023 J/cm3) within a rather low dielectric loss (0.015) and leakage current density (4.41 E−8 A/cm2), and the storage is 1.82 times higher than that of the pure PVDF. This improvement in energy storage of composites should be attributed to the occurrence of Al2O3 shell which effectively prevented the leakage current and resulted the reducement in the dielectric loss of the composites.

High-dielectric constant enhanced photon–exciton coupling in an evanescent vacuum

Electromagnetic vacuum engineering in nanostructures can be used to tailor the light–emitter interaction at the subwavelength scale. Here, by embedding a nanocavity quantum electrodynamic system in an evanescent vacuum, we theoretically investigate high-dielectric constant enhanced photon–exciton coupling. The evanescent depth decreases as the dielectric constant of the embedding medium increases. Thus, more confined evanescent fields are obtained owing to faster exponential decay of an evanescent wave, which is used to obtain a larger coupling coefficient enhancement. The enhanced coupling coefficients are also demonstrated by changing the Ag nanorod size and the gap distance between the nanoparticle and plate. To significantly enhance the absolute value of the coupling coefficients, the Ag cylindrical nanorod can be replaced by the Ag pyramid or bipyramid. Evanescent vacuum induced strong photon–exciton coupling would have a significant influence on the fundamental physics of the subwavelength-confined cavity quantum electrodynamics and on-chip quantum information processing and scalable quantum networks.

Quantitative Surface-Enhanced Raman Spectroscopy through the Interface-Assisted Self-Assembly of Three-Dimensional Silver Nanorod Substrates.

The realization of surface-enhanced Raman spectroscopy (SERS) to be a reliable quantitative analytical technique requires sensitive and reproducible enhancing substrates. Here, uniform three-dimensional (3D) Ag nanorod (AgNR) substrates with well-defined interlayer spacings are prepared through the air-liquid interface-assisted self-assembly of AgNR in a layer-by-layer manner. The correlation of the SERS performance with the 3D AgNR structures is performed by SERS mapping the substrates. SERS mapping reveals the excellent enhancement uniformity of the 3D substrates with the relative standard deviation (RSD) less than 10%. It finds that both of the number of layers (NL) and the length of the AgNR have effects on the SERS performance of the 3D AgNR substrates. It is demonstrated that the intergaps between layers contribute much to the SERS intensity of the 3D AgNR by creating the interlayer (out-of-plane) plasmonic coupling. The impact of the excitation wavelengths (532, 633, and 785 nm) on SERS performance is also determined. The optimal 3D AgNR structures achieved by the correlation study is further used to detect a set of related molecules (l-tryptophan (Trp), l-phenylalanine (Phe), urea, and melamine). The 3D AgNR SERS of the analytes exhibits linear responses over wide concentration ranges. The sensitivity of the 3D AgNR SERS is proved by comparing to that of the current methods. Moreover, the 3D AgNR substrates maintain the performance stability during 4 weeks of storage.

Surface plasmon resonance effect for a new structure of Ag/WO3 nanorod-shell nanocomposits and application in smart window

New chromogenic structures such as hybrids and nanocomposites can be enhanced the electrochromic performance due to wide interest on account of their potential application values in smart window, low-power display, automobile anti-reflect mirror and electronic papers. In this study, we synthesized the Ag nanorods with different aspect ratios by hydrothermal method. The synthesized Ag nanorods with different sizes are covered by tungsten oxide shells in two steps (Ag1-W, Ag2-W and Ag3-W). The different size of Ag particles exhibit different surface palsmon effect and subsequently this phenomenon effects on electrochromic results. Electrochromic performance of Ag/WO3 nanorod-shell thin films on FTO-coated glass substrates are investigated in 1 M solution of LiClO4-PC as electrolyte in visible region. In particular, a significant optical modulation (32.33%, 33.60% and 36.81% at 633 nm, fast switching speed (5.7 s-6.3 s, 5.3 s-5.7 s and 5.0 s-5.5s for colored-bleached states) and high coloration efficiency (100, 78.9 and 94.28 cm2C-1 at 633 nm) are achieved for these structures.

Plasmonic Effects of Silver Nanoparticles Embedded in the Counter Electrode on the Enhanced Performance of Dye-Sensitized Solar Cells.

The plasmonic effects of silver (Ag) nanoparticles (NPs) with various morphologies (sphere, rod, and prism) embedded into the platinum (Pt) counter electrodes (CEs) of dye-sensitized solar cells (DSCs) were systematically investigated. It was shown that the power conversion efficiencies (PCEs) of the incorporated devices are notably improved from 7.60%, for the reference device without Ag NPs, to 8.10, 8.68, and 8.55% with Ag nanospheres, nanorods, and nanoprism devices, respectively. Moreover, the photocurrent and fill factor enhancement is attributed to the better optical and electrical properties of the integrated devices. Among all of the NP morphologies studied, Ag nanorods offer the best improvement to the device efficiency, as they have longitudinal localized surface plasmon resonance (L-LSPR) and strong scattering effects correlate within the morphology.