Ag Nanorod Arrays Research Articles

3D SERS Substrate of Z-Shaped Ag Nanorod Array for Thiabendazole Detection.

Ag nanoparticles sputtered on silicon wafer are used as masks for the fabrication of silicon columns by ion etching, which induces the growth of the inclined Ag nanorod by inclined Ag sputtering. V-shaped and Z-shaped Ag nanorods can be obtained by varying incline angles and deposition times. SERS detection and FDTD simulation are used to compare and investigate the enhanced electromagnetic coupling of incline nanorod arrays with different shapes in three-dimensional space, which indicates that Z-shaped nanorods show good SERS properties. The Z-shaped Ag nanorod array is used as a SERS substrate for the detection of thiabendazole with a concentration down to 10-11 M.

SERS/electrochemical dual-mode biosensor based on multi-functionalized molybdenum disulfide nanosheet probes and SERS-active Ag nanorods array electrodes for reliable detection of cancer-related miRNA

The reliable detection of cancer-related biomarkers is essential for accurate diagnosis of cancers. SERS/electrochemical dual-mode sensing can provide a powerful tool to achieve more accurate detection, however, the in situ facile dual-mode detections have rarely been reported. Herein, a novel SERS/electrochemical dual-mode biosensor based on multi-functionalized molybdenum disulfide nanosheet (mF-MoS2 NS) probes and SERS-active Ag nanorods (AgNRs) array electrode was proposed for in situ dual-mode detection of gastric cancer-related miR-106a. The AgNRs array coated by the mF-MoS2 NSs shows significantly improved electrochemical and SERS stability in electrolyte solutions, and the “mF-MoS2 NSs probes-miRNA-AgNRs array electrodes” sandwich structured SERS/electrochemical sensor was built for stable, in-situ dual-mode detection of miR-106a. The sensor shows good selectivity for differentiating miR-106a from the single-base mismatched nucleic acid, and possesses linear calibration curves of both SERS and electrochemical sensing modes with the limit of detections of 67.44 fM and 248.01 fM, respectively. The reliable assay of miR-106a in human serum indicates that the proposed SERS/electrochemical dual-mode sensor is suitable for detecting complex samples and can be a potential high-sensitive and reliable tool for clinical diagnosis of early cancers.

Ultrafast changes in effective permittivity of hyperbolic metamaterials and related multi-resonance-induced ultrafast process excited by femtosecond pulses.

Hyperbolic metamaterials (HMMs) exhibit rich optical nonlinear responses for the epsilon-near-zero (ENZ) and anisotropy. In this study, we extract the time-dependent change in the effective permittivity of an Ag nanorod array under femtosecond pulses pumping around its ENZ wavelength. The transmittance and transient absorption spectra measured by s- and p-polarizations are used in the extraction process. We experimentally confirm the existence of an ultrafast recovery process with a relaxation time of 0.24 ps in the transient absorption spectra. The calculation based on the extracted nonlinear effective permittivity indicates that the ultrafast signal originates from the superposition of two slower recovery processes, with relaxation times of 0.74 ps and 1.19 ps, respectively. The results indicate that when the responses of two nonlinear processes have different signs and recovery speeds, their superposition may cause faster signal recovery in the combined process than in the two individual processes.

High-performance photonic spin Hall effect in anisotropic epsilon-near-zero metamaterials.

A high-performance photonic spin Hall effect is demonstrated in an anisotropic epsilon-near-zero (ENZ) metamaterial based on the wave-vector-varying Pancharatnam-Berry phase. The giant out-of-plane anisotropy of ENZ metamaterial induces strong spin-orbit coupling. With a small incident angle, photons with opposite spins move along opposite transverse directions gradually. After transmitting through a submicrometer thick ENZ metamaterial, the spin photons are fully separated with a spin separation of 2.7 times beam waist and transmittance of 70.1%, allowing a figure of merit F up to 1.9. A practical ENZ metamaterial consisting of an Ag nanorod array is proposed, whose figure of merit is still up to 0.006. This high-performance photonic spin Hall effect provides an integrated and practical way for the development of spin-photonic devices.

Interaction between plasmonic silver nanorod arrays and nanosecond pulsed laser

Plasmonic metamaterials have recently received increasing attention due to their favorable optical and electrical properties. The physics of the interaction between plasmonic metamaterials and lasers are rich and open opportunities for applications, such as sensing, imaging and photovoltaics. Here, we investigate the mechanism of the interaction between Ag nanorod arrays and nanosecond (ns) pulsed laser. The experimental results show that ns laser pulses significantly improve the crystallinity of the Ag nanorod arrays. Meanwhile, the laser evaporates some of the Ag into the air. This work paves the way for future high-performance plasmonic meta-devices.

Multilayer thin-film flake dispersion gel for surface-enhanced Raman spectroscopy

Ag nanorod arrays/dielectrics/mirror-structured multilayer thin-film are well known, highly sensitive surface-enhanced Raman scattering (SERS) substrates that enhance the Raman scattering cross-section by the interference of light. However, extracting biomarkers directly from human skin using these solid substrates is difficult. To overcome this problem, we propose a multilayer thin-film flake dispersion gel by centrifugal mixing of the multilayer thin-film and hydroxyethyl cellulose (HEC) gel. The multilayer thin-film was prepared by serial bideposition using the dynamic oblique angle deposition technique. The mixing process was optimized to obtain flakes of ~10 {\mu}m so that the optical properties of the multilayer film can be preserved, and there is no risk of adverse effects on humans. The SERS features of the flakes dispersion gel were tested using 4, 4'-bipyridine (BPY). The BPY molecules diffused through the highly porous gel within a few seconds, generating significant SERS signals. The multilayer film flakes dispersion gel showed a SERS signal about 20 times better than the gel-dispersed Ag nanorod arrays without a multilayer film structure. These SERS active flakes dispersion gel can be used directly on the skin surface to collect body fluids from sweat, for biomarker sensing.

Design of Armrest Ag Nanorod Arrays with High SERS Performance for Sensitive Biomolecule Detection

To enlarge the surface enhanced Raman scattering(SERS) enhancement of Ag nano-pillar arrays, a well-controlled armrest Ag NRs@Al2O3 structure was designed, aiming at triggering efficient resonance ...

Self-sustainable and recyclable Ag nanorods for developing Ag-Ag2S nano heterostructures using sewage gas: Applications in photocatalytic water purification, hydrogen evolution, SERS and antibacterial activity

Multifunctionality and recyclability of Ag nanorods array (well known tas potential SERS substrates) have been explored for other imperative applications like water purification by photocatalytic dye degradation, hydrogen evolution, antibacterial activity, and SERS based detection after sulfurization. An easy and green approach of exposing the Ag nanorods array to sewage H2S gas has been applied for sulfurization. This resulted in multifunctional Ag-Ag2S nanoheterostructures manifesting a metal-semiconductor heterojunction with exceptional optical, electronic and photocatalytic properties. The Ag nanorods array on glass as well as ITO substrates were fabricated by glancing angle deposition technique and then sulfurized by exposing to a sewage site, resulting in Ag-Ag2S nanoheterostructures at ambient conditions and confirmed by several morphological, structural and elemental characterization tools. The fabricated nanoheterostructures are utilized efficiently for important applications including dye degradation under visible light irradiation within 30 min, photoelectrochemical reaction for hydrogen evolution, surface enhanced Raman scattering based detection and significant bactericidal effect. The salient features of synthesized Ag-Ag2S nano-heterostructures comprise an important self-sustainable approach which is pivotal in the present research scenario that requires significant multidimensional applications.

Generalized ellipsometry characterization of Ag nanorod arrays prepared by oblique angle deposition

Silver nanorods arrays (AgNRs) prepared by oblique angle deposition were characterized by the generalized ellipsometry method in the spectral range from 370 to 950 nm. Three structure models were used to fit the ellipsometry data, the uniaxial model, the biaxial orthorhombic model, and the biaxial monoclinic model. Unlike the uniaxial model reported in most literature, the biaxial models are found to give better fitting results. The optical properties along the three principle axes are different: along long axis it displays predominantly metallic behavior; along one short axis it approaches to a lossless dielectric while along the other it behaves as an absorbance dielectric. The AgNRs also demonstrate epsilon-near-zero property with the real part of dielectric constant along the rod being very close to zero at wavelength of 416 nm, which is expected to be tuned with changing of the vapor incident angles.

Surface-enhanced Raman scattering of monolayer transition metal dichalcogenides on Ag nanorod arrays.

In this work, we studied surface-enhanced Raman scattering (SERS) of MS2 (M=Mo, W) monolayers that were transferred onto Ag nanorod arrays. Compared to the suspended monolayers, the Raman intensity of monolayers on an Ag nanorod substrate was strongly enhanced for both in-plane and out-of-plane vibration modes: up to 8 (5) for E2g and 20 (23) for A1g in MoS2 (WS2). This finding reveals a promising SERS substrate for achieving uniform and strong enhancement for two-dimensional materials in the applications of optical detecting and sensing.

Ultrasensitive SERS determination of avian influenza A H7N9 virus via exonuclease III-assisted cycling amplification

The avian influenza A H7N9 virus is known as one of the newly discovered highly pathogenic avian influenzas with serious threat to public health and the poultry industry. In this work, an ultrasensitive surface-enhanced Raman scattering (SERS) determination of H7N9 virus via exonuclease III-assisted cycling amplification was proposed to meet the needs of rapid, sensitive and accurate detection of H7N9-related genes. The SERS strategy aims to simultaneously determine the characteristic gene fragments of H7 and N9 by specially designing Capture, Replace, and Probe single-strand DNAs to realize exonuclease III-assisted cycling amplifications, and then integrating the cyclic amplification with SERS-active Ag nanorods array substrate to achieve an ultrasensitive SERS determination of H7N9. After characterizing the effectiveness of the sensing mechanism and further investigating the surface blocking and the dosage of exonuclease III, the optimal surface blocking was achieved by using 10 μM and 100 μM mercaptohexanol for H7 and N9 detection respectively, and the optimal Exo III concentrations for sensing H7 and N9 were 0.10 U μL−1 and 0.30 U μL−1 respectively. Under the optimal conditions, dual and specific detections of H7 and N9 gene fragments were obtained with detection linear interval from 1 fM to 100 pM and limit of detections low to 31 aM of H7 and 44 aM of N9, as well as recovery in the range of 93.8–106.2% with relative standard deviation less than 6.12%. The proposed ultrasensitive SERS strategy can provide a powerful tool for determining H7N9 virus and other avian influenza viruses.

Recyclable three-dimensional Ag nanorod arrays decorated with O-g-C3N4 for highly sensitive SERS sensing of organic pollutants.

A three-dimensional (3D) substrate was developed by assembling a monolayer of graphitic carbon nitride (O-g-C3N4) on Ag nanorod arrays (Ag NRs) for sensitive and recyclable surface enhanced Raman scattering (SERS) detection. The prepared Ag NRs/O-g-C3N4 substrate not only generated a significant Raman enhancement effect as a result of the strong π-π stacking interaction between O-g-C3N4 and the analytes but also possessed excellent self-cleaning property via visible-light irradiation that was attributed to its outstanding catalytic performance. Highly sensitive SERS detection could be achieved with a LOD of 8.2 × 10-10 M for R6 G, and the substrate could be used repeatedly for at least four cycles with tolerable intensity attenuation. In addition, the 3D substrate exhibited long-term stability originating from the electron-donor effect of O-g-C3N4 and high reproducibility due to the uniform decoration of O-g-C3N4 on the Ag NRs through the strong interaction. Furthermore, using Ag NRs/O-g-C3N4, the recyclable detection of antibiotics in a water sample was demonstrated with high sensitivity, which indicates that the 3D Ag NRs/O-g-C3N4 substrate is a promising candidate for eliminating the challenges of single-use SERS substrates and building a portable SERS platform to sense organic molecular species.

Dipole Radiation-Induced Extraordinary Optical Transmission for Silver Nanorod-Covered Silver Nanohole Arrays

A new extraordinary optical transmission (EOT) mode is discovered when a hexagonal Ag nanohole array is covered by a tilted Ag nanorod array. The resonant wavelength of this EOT mode red-shifts with respect to the normal EOT mode predicted by plasmon-grating coupling theory or dynamic scattering theory and increases linearly with the nanorod length. The structures also show strong polarization dependence; i.e., when the electric field (E-field) direction of the incident light is perpendicular to the long axis of the nanorods, only normal EOT spectrum is visible, but when the E-field is parallel to nanorod axis, the new mode appears. Our finite-difference-time-domain calculations confirm this finding and show that this new mode is due to the dipole radiation of the nanorods on top of the nanoholes. It is expected that other complicated unit cells of nanohole arrays could generate other new EOT modes and can be used to design new optical devices.

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.

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.

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.

Highly sensitive VOC gas sensor employing deep cooling of SERS film

AbstractThe potential of surface‐enhanced Raman spectroscopy (SERS) as a highly sensitive and selective gas sensor was investigated experimentally. Especially, the relation between the temperature of a SERS film and gas adsorption or signal intensity was observed systemically and quantitatively, from which the enhancement of gas adsorption and signal intensity by up to 40 times was observed with the SERS film temperature of approx. −80 °C, which corresponds to theoretical anticipation and leads to detection sensitivity defined by limit of detection in 3σ ~1 ppb in case of benzene gas within 2‐min acquisition time. For SERS, Ag nanorod array films functionalized by propanethiol and a spectrometer with a fiber Raman probe and 785‐nm pump laser were employed. The target volatile organic compound gas was benzene. The detection sensitivity of the SERS sensor was ~1 ppm at room temperature within 2‐min acquisition time.

HfO2-wrapped slanted Ag nanorods array as a reusable and sensitive SERS substrate for trace analysis of uranyl compounds

SERS has been used for rapid and trace analysis of uranyl compounds due to its fast response and high sensitivity. However, the difficulties in preparing stable and reusable SERS substrate as well as quantitative detection severely restrict its practical application prospects. Herein, HfO2-wrapped slanted Ag nanorods array was used as SERS substrate for sensitive analysis of trace uranyl compounds for the first time. The proposed substrate with uniform surface roughness and well-distributed Ag nanorods showed excellent spectral reproducibility, while the ultrathin HfO2 film fully covering Ag nanorods effectively improved the substrate stability and contributed to its cyclic utilization. Besides, quantitative detection of trace uranyl ions was achieved by using this substrate with an ultra-low detection limit of 8.33 ppb. Most importantly, SERS spectra of varied uranyl hydroxides at different pH values together with in situ SERS spectrum of UO2(CO3)34− were recorded on this substrate, building the correspondence between SERS band position of OUO(ν1) and uranyl species. Thus, SERS technique based on this substrate could be a promising method for both concentration detection of uranyl ions and structure identification of some uranyl compounds in trace level, indicating high potential application prospects in the environmental monitoring.

Dielectrophoresis-Based Protein Enrichment for a Highly Sensitive Immunoassay Using Ag/SiO2 Nanorod Arrays.

A nanoscale insulator-based dielectrophoresis (iDEP) technique is developed for rapid enrichment of proteins and highly sensitive immunoassays. Dense arrays of nanorods (NDs) by oblique angle deposition create a super high electric field gradient of 2.6 × 1024 V2 m-3 and the concomitant strong dielectrophoresis force successfully traps small proteins at a bias as low as 5 V. 1800-fold enrichment of bovine serum albumin protein at a remarkable rate of up to 180-fold s-1 is achieved using oxide coated Ag nanorod arrays with pre-patterned sawtooth electrodes. Based on this system, an ultrasensitive immunoassay of mouse immunoglobulin G is demonstrated with a reduction in the limit of detection from 5.8 ng mL-1 (37.6 pM) down to 275.3 fg mL-1 (1.8 f M), compared with identical assays performed on glass plates. This methodology is also applied to detect a cancer biomarker prostate-specific antigen spiked in human serum with a detection limit of 2.6 ng mL-1 . This high sensitivity results from rapid biomarker enrichment and metal enhanced fluorescence through the integration of nanostructures. The concentrated proteins also accelerate binding kinetics and enable signal saturation within 1 min. Given the easy fabrication process, this nanoscale iDEP system provides a highly sensitive detection platform for point-of-care diagnostics.

SERS polarization-dependent effects for an ordered 3D plasmonic tilted silver nanorod array.

Hexagonal close-packed tilted Ag nanorod arrays that exhibit excellent uniformity and reproducibility were prepared. The tilt angle was easily controlled by regulating the sputtering angle, accompanied by a reduction and constancy in the gap size of adjacent nanorods, which is 30° and 90° relative to the sputtering direction. The surface enhanced Raman spectroscopy (SERS) technique was used to characterize the interaction of tilted Ag nanorod arrays with polarized laser excitation. Interestingly, the SERS polarization-dependence increased with increasing tilt angle of the Ag nanorods. To elucidate the essential factors responsible for this SERS result, three-dimensional (3D) electromagnetic enhancement distribution for the proposed system was numerically simulated based on p- and s-polarization excitation. Most importantly, the fundamental reasons for the polarization dependence of SERS were obtained by a quantitative 3D numerical simulation of hotspot distribution for adjacent nanorods.