Ag Nanorods Research Articles

A Tuneable and Easy-to-Prepare SERS Substrate Based on Ag Nanorods: A Versatile Tool for Solution and Dry-State Analyses

Surface-enhanced Raman spectroscopy is a powerful technique for the ultra-sensitive detection of organic analytes. In this paper, the preparation of SERS substrates based on silver nanorods (AgNRs) is proposed, exploiting a simple protocol which does not require complex procedures and/or sophisticated and expensive instrumentation. For this purpose, various syntheses of AgNRs were tested, and the best one for preparing the SERS active substrate proved to be the one which does not involve surfactants as nanoparticle stabilizers. The plasmonic properties of the selected substrate can be modified based on the concentration of the deposited nanoparticles, allowing for the experimentation of different excitation wavelengths. Positive results were obtained on reference solutions of three natural dyes of historical interest using both green exciting radiation (532 nm) and two near-infrared ones (785 and 850 nm; the latter is combined with the SSE™ technology for further fluorescence quenching). Furthermore, the substrates of AgNRs were found to be suitable for SERS measurements even in dry-state conditions, i.e., only exploiting the electromagnetic interaction between the nanostructured substrate and the dye molecules absorbed onto a wool fibre.

Plasmon-mediated photocatalytic conversion in Au or Ag nanorod aggregates by surface-enhanced Raman spectroscopy

Plasmonic nanoparticles (NPs) hold considerable potential as photocatalysts owing to their robust light–matter interactions across diverse electromagnetic wavelengths, which significantly influence the photophysical characteristics of the adjacent molecular entities. Despite the widespread use of noble-metal NPs in surface-enhanced Raman scattering (SERS) applications, little is known about the kinetics of nanoparticle aggregation and how it affects their configurations. This study investigates the plasmon-driven photochemical conversion of 4-nitrobenzenethiol (NBT) to 4,4′-dimercaptoazobenzene (DMAB) on Au and Ag nanorods (NRs) through SERS. Significantly, photoconversion phenomena were observed on Ag NRs but not on Au NRs upon laser excitation at 633 nm. Finite-difference time-domain simulations revealed the presence of stronger electromagnetic fields on Ag NRs than on Au NRs. The aspect ratios and gaps between individual NPs in dimer configurations were determined to elucidate their effects on electromagnetic fields. The Ag NR dimer with an end-to-end configuration, an aspect ratio of 3.3, and a 1-nm gap exhibited the highest enhancement factor of 1.05 × 1012. Our results demonstrate that the primary contribution from diverse configurations in NR aggregates is the end-to-end configuration. The proposed NP design with adjustable parameters is expected to advance research in plasmonics, sensing, and wireless communications. These findings also contribute to the understanding of plasmon-driven photochemical processes in metallic nanostructures.

Localized surface plasmon-enhanced nanorod micro-LEDs with Ag nanoparticles embedded in insulating and planarizing spin-on glass

To enhance the emission of GaN-based Micro-LEDs (μLEDs), we etched uniform nanorods (NRs) on the μLED surface and filled the nanorod gaps with spin-on glass (SOG) containing mixed Ag nanoparticles (NPs). The nanorod structure creates a conducive environment for close interaction between Ag NPs and quantum wells (QWs), facilitating the coupling of Ag NPs as localized surface plasmons (LSPs) with the QWs to enhance light emission. The SOG acts as an insulating layer between Ag NPs and NRs, preventing electron leakage, while also serving as a planarization material for the nanorod structure. This configuration allows for the fabrication of a planar Indium Tin Oxide layer without short-circuiting the nanorod structure. Compared to traditional planar Micro-LEDs, NR-μLEDs with SOG-encased Ag NPs exhibit a 50% increase in electroluminescence (EL) intensity and a 56% increase in photoluminescence (PL) intensity. This work paves the way for broader applications of LSP in μLEDs.

Real-time imaging reveal anisotropic dissolution behaviors of silver nanorods

The morphology and size control of anisotropic nanocrystals are critical for tuning shape-dependent physicochemical properties. Although the anisotropic dissolution process is considered to be an effective means to precisely control the size and morphology of nanocrystals, the anisotropic dissolution mechanism remains poorly understood. Here, using in situ liquid cell transmission electron microscopy, we investigate the anisotropic etching dissolution behaviors of polyvinylpyrrolidone (PVP)-stabilized Ag nanorods in NaCl solution. Results show that etching dissolution occurs only in the longitudinal direction of the nanorod at low chloride concentration (0.2 mM), whereas at high chloride concentration (1 M), the lateral and longitudinal directions of the nanorods are dissolved. First-principles calculations demonstrate that PVP is selectively adsorbed on the {100} crystal plane of silver nanorods, making the tips of nanorods the only reaction sites in the anisotropic etching process. When the chemical potential difference of the Cl− concentration is higher than the diffusion barrier (0.196 eV) of Cl− in the PVP molecule, Cl− penetrates the PVP molecular layer of {100} facets on the side of the Ag nanorods. These findings provide an in-depth insight into the anisotropic etching mechanisms and lay foundations for the controlled preparation and rational design of nanostructures.

Seed-Mediated Electrodeposition of Silver Nanowires and Nanorods.

Here, we compare the amount and morphology of silver (Ag) nanostructures electrodeposited at varied potentials and times in the presence of cetyltrimethylammonium bromide (CTAB) onto glass/indium tin oxide (glass/ITO) electrodes functionalized with mercaptopropyltrimethoxysilane (MPTMS) and coated or not coated with 4 nm average diameter Au nanoparticle (Au NP) seeds. There is a significantly larger amount of Ag deposited on the seeded electrode surface compared to that in the nonseeded electrode at potentials of -150 to -300 mV (vs Ag/AgCl) since the Au NP seeds act as catalysts for Ag deposition. At more negative overpotentials of -400 to -500 mV, the amount of Ag deposited on both electrodes is similar because the deposition kinetics are fast enough on glass/ITO that the Au seed catalyst does not make as big of a difference. Ag nanorods (NRs) and nanowires (NWs) form on the seeded surfaces, especially at more positive potentials, where deposition primarily occurs on the Au seed catalysts. Deposition of Ag onto the Au seeds appears as a separate peak in the voltammetry. This procedure mimics the seed-mediated growth of Ag NRs observed in solution in the presence of CTAB using ascorbic acid as a reducing agent. The yield, length, and aspect ratio of the Ag NRs/NWs depend on the deposition time and potential with the average length ranging from 300 nm to 3 μm for times of 30-120 min and potentials of -150 to -200 mV. The electrochemical seed-mediated growth of Ag NRs/NWs across electrode gaps could find use for resistive and surface-enhanced Raman-based sensing and molecular electronic applications.

Reversal of optical binding force on a plasmonic heterodimer with dipole–dipole type Fano resonance

In the present work, we theoretically and numerically investigate the near field optical binding force on Au–Ag nanorod heterodimers, which can support the electrical dipole–dipole type Fano resonance, under a normally plane wave or polarized laser beam. The numerical results show that the optical binding force between the heterodimer can be reversed near the position of the Fano dip when the incident wave is polarized along the dimer axis, indicating an attractive to repulsive transition. Compared with the Au–Ag heterodimer, the Au and Ag homodimers with the same material show no repulsive binding force. Using the multipole decomposition method, we find that the sign of optical binding force is completely determined by the phase difference of the separated electric dipole plasmon modes excited in the different particles, which can be strongly affected by the wavelength of the incident wave. In addition, we demonstrate the effects of three geometrical parameters (including the length, radius, and gap of the heterodimer) on the Fano-mediated optical binding force in detail. Finally, the numerical results indicate that the reversal of attractive and repulsive forces can also be obtained when the heterodimer is illuminated with a laser beam. Our findings are important for not only a deep understanding of plasmonic-mediated optical binding force but also stable optical manipulation of the plasmonic particles.

Electrophoretic deposition of photothermal responsive antibacterial coatings on titanium with controlled release of silver ions

Burst release of antibacterial agents generated by the surface antibacterial modification of Ti implants frequently results in a reduction in their biocompatibility and substantial toxic side effects. In this study, core-shelled nanoparticles namely AgNR@MSN, were synthesized successfully by mesoporous silica shell in-situ encapsulated Ag nanorods, and then co-deposited with chitosan to form a AgNR@MSN-chitosan composite coating on Ti substrate by electrophoretic deposition. The developed composite coating, due to the presence of AgNR, presented excellent photothermal effect under the irradiation of an 808 nm near-infrared laser, leading to both rapid increase of local temperature and triggered release of Ag ions for bacterial-killing effect against both E. coli and S. aureus. The addition of AgNR@MSN also improved the wettability of the coating and the MSN shell with mesoporous tunnels could barrier the contact and release rate of Ag to improve the biocompatibility. The developed photothermal responsive coating could be considered as a promising platform for achieving controlled release of Ag ions with outstanding antibacterial and biocompatible properties.

Highly efficient sunlight-driven LSPR-enhanced core-shell Ag dendrite/g-C3N4 composite photocatalysts

Noble metal nanostructures with localized surface plasmon resonance (LSPR) effect can be employed to enhance the light absorption ability of photocatalysts. However, it has been a challenge to control the size and morphology of noble metal nanostructures to manipulate the LSPR wavelength and improve the performance of photocatalysts. Herein, an Ag dendrite (AgD) composed of Ag nanorods with different sizes was facilely constructed by a displacement reaction, and sunlight-driven LSPR-enhanced core-shell AgD/g-C3N4 composite photocatalysts (AgD-CN) were synthesized by thermal polymerizing mixtures of melamine and different amounts of AgD. This core-shell AgD-CN improved the stability of AgD and made full use of the near-field enhancement effect of AgD’s LSPR, resulting in a broad light absorption band. AgD-CN-15 showed the highest photogenerated electron-hole pair separation rate and the best photocatalytic performance when the addition amount of AgD was 3 wt%. The degradation rate of RhB by AgD-CN-15 reached 95.20% after sunlight irradiation for 60 min, and its reaction rate constant was 5.2 times that of the pristine g-C3N4. Moreover, ·OH, h+ and ·O2- were found to be the main active species. AgD is easy to prepare and can broaden the light absorption wavelength range and significantly enhance light absorption ability of photocatalysts, which provides a new method to improve the performance of LSPR-enhanced photocatalysts.

Ag nanorod@PEI-Ag nanohybrid as an excellent signal label for sensitive and rapid detection of serum HER2

The accurate detection of Human epidermal growth factor receptor-2 (HER2) as a critical breast cancer biomarker can be essential for the early selection of therapeutic approaches. HER2 is a prominent component of a signaling network. Overexpression of the HER2 protein due to amplification of its gene leads to the development of an aggressive subtype of breast cancer. Patients with tumors that overexpress HER2 are eligible for treatment that significantly reduces mortality rates. Herein, we present a fast and simple method for detecting serum HER2. A new electrochemical label has been developed using charged Ag nanorod@ polyethylenimine-Ag (Ag NR@ PEI-Ag) nanohybrid. The synthesized Ag NR@PEI-Ag nanohybrid simultaneously has the electroactive property of silver and the large surface area of the PEI, which results in the enhancement of the detection signal. So, using Ag NR@PEI-Ag nanohybrid as the electrochemical label, a simple, fast, and sensitive electrochemical biosensor was designed to detect HER2. This way, after immobilizing HER2 aptamer on the Au electrode surface, HER2 or human serum was exposed to the aptamer. Then, the positively charged Ag NR@PEI-Ag nanohybrid was adsorbed onto the negatively charged aptamer-HER2 complex, and the current that was produced due to the Ag/AgCl reaction was measured as the electrochemical signal. The aptasensor shows a broad linear response from 10–12 to 10–7 g, a low detection limit (LOD) of 10 pg, and a total assay time of ~ 30 min.

Bright and dark plasmon resonance of Ag nanorod dimers

In this paper, plasmon resonances arising from the interaction between two closely spaced nanoparticles have been investigated by the finite difference time domain method. We report that the plane wave directly excites the bright mode and dark mode in the symmetric Ag nanorod dimers. We study the spectral properties of plasmonic nanorod systems by selectively tailoring the nanorod geometry parameters and interparticle gap distance. We also study the modulation of the geometry parameters and gap distances of nanorods on the charge density and electric field distributions of both the resonance modes. We believe that unlocking these properties will inspire further exciting developments in quantum mechanical effects and sub-nanometer scale photonics.

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.

Nano-engineered silver rods from Pleurolobus gangeticus root extract and their antilithiatic and cytoprotective role on oxalate injured renal epithelial cells

The green synthesis of nanoparticles and their specific role in the field of medicine are getting humongous attention worldwide. Their eco friendly and non toxic behaviour gives them such immense priority in the field of medicines. In our study, we explored the antiurolithiatic potential of green synthesized Ag nanorods (AgNRs) from the root extract of Pleurolobus gangeticus (L.) J. St.- Hil. Ex H. Ohashi & K. Ohashi.(PG) on oxalate-induced injury to renal tubular epithelial cells. The extract obtained from P. gangeticus were successfully reduced to silver ions and silver nanorods were synthesized further. The PG derived AgNRs were characterized using UV–Visible Spectroscopy (UV–Vis), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Diffraction analysis (XRD), Dynamic Light Scattering (DLS) and Scanning Electron Microscopy (SEM). The results revealed that the synthesized silver nanoparticles are rod shaped nano clusters with an average diameter of 100–200 nm and an average length of 3–4 μm with a poly dispersive index value of 0.214. The AgNRs at a concentration of 500 μg/mL showed promising inhibitory potential on the CaOx crystals in a dose dependent manner with a maximum absorption of 0.178 ± 0.08. The AgNRs also showed potent cytoprotective effects on oxalate-induced Madin-Darby Canine Kidney (MDCK) renal epithelial cells in a dose dependent manner via reducing the reactive oxygen species (ROS) generation in the cells. Overall, our findings suggest the role of PG derived AgNRs as a potent source of antiurolithiatic agents and open a wide range of possibilities in the use of silver nanosystems for the treatment of urolithiasis.

The Influence of Nonlocal Metal-Dielectric Environments on Physical and Chemical Processes.

ConspectusPlasmonic nanolayers and laminar metallic/dielectric multilayers were originally developed for optical cloaking applications and lensing applications that could potentially image objects whose size was below the diffraction limit. These assemblies were initially formed from gold or silver nanorods grown within an alumina mesh. However, more recently, assemblies with similar properties have also been prepared by sequential thin-layer deposition of alternating layers of gold and magnesium fluoride (MgF2). These metal/dielectric composite materials enable control of the dielectric constant in the directions perpendicular to the layers and balance the real and imaginary dielectric constants of the assembly such that the speed and the amplitude of the waves traveling through the assembly are not attenuated.In this Account, we will also focus on a few of the applications ranging from surface wetting to fluorescence quenching to enhancement of photochemical reactions. First, we will share an introduction to processes used to create these materials, which are combinations of low refractive index metals and transparent higher index materials arranged in a scalable repeating fashion. Two fabrication methods were employed: an electrochemical deposition of Ag nanorods into an anodized alumina matrix which produced materials with an anisotropic negative refractive index material within the plane of the film and lamellar metal/dielectric layers in which the negative index perpendicular to the growth direction. These alternating layers of plasmonic metals and dielectric materials were ultimately chosen to prepare films for further testing, because of their relative ease of fabrication. We will continue with a discussion of a few of the applications of both of these nonlocal dielectric composite materials including more specialized plasmonic, composite, and hyperbolic metamaterials including fluorescence quenching, photochemical reactions, and surface wetting. In each of these applications, the unique response caused by the enhancement of the electric field and the interface between hyperbolic materials and plasmonic materials as they interact photophysically with their near neighbors is presented. In each of the applications, the enhanced electric field extends from the composite substrate layer to interact with its near neighbors and beyond. The presence of this extended interaction can be observed in the form of decreased emission lifetime, enhancement of photochemical reaction rates, and changes in the surface energies measured by contact angle goniometry. In this Account, all of these situations will be addressed. Finally, we will conclude with a summary and vision for the future as well as a discussion of the unique challenges and opportunities available as research active faculty at an HBCU.

Investigating the effect of aligned Ag nanorods on para-aramid woven fabric and anisotropy in inter-yarn friction

Inter yarn friction, measured in terms of yarn pull-out force, is a major mechanism of energy absorption in soft body armor. Increasing inter-yarn friction of para-aramid fabric to improve ballistic performance without adding weight is challenging. This work reports the fabrication of aligned Ag nanorods (AgNRs) on the para-aramid (Kevlar) fabric surface using the glancing angle deposition technique. A single yarn pull-out test examines Kevlar fabric treatment. The AgNRs-coated para-aramid fabric retains its flexibility and weight while increasing yarn pull-out force by 130%. Anisotropy in inter-yarn friction depends on the yarn's sliding direction relative to Ag nanorod tilt direction, indicating direction-dependent yarn pull-out force. The periodic character of pull-out response post-peak force is replicated by modeling the yarn pull-out phenomenon by incorporating a mesoscale level numerical model of woven fabric. The numerical model confirms the experimental results that formation of nanorods significantly increases inter-yarn friction and pull-out force.

Routing the Exciton Emissions of WS2 Monolayer with the High-Order Plasmon Modes of Ag Nanorods.

Locally routing the exciton emissions in two-dimensional (2D) transition-metal dichalcogenides along different directions at the nanophotonic interface is of great interest in exploiting the promising 2D excitonic systems for functional nano-optical components. However, such control has remained elusive. Herein we report on a facile plasmonic approach for electrically controlled spatial modulation of the exciton emissions in a WS2 monolayer. The emission routing is enabled by the resonance coupling between the WS2 excitons and the multipole plasmon modes in individual silver nanorods placed on a WS2 monolayer. Different from prior demonstrations, the routing effect can be modulated by the doping level of the WS2 monolayer, enabling electrical control. Our work takes advantage of the high-quality plasmon modes supported by simple rod-shaped metal nanocrystals for the angularly resolved manipulation of 2D exciton emissions. Active control is achieved, which offers great opportunities for the development of nanoscale light sources and nanophotonic devices.

The optical properties of nanorods with curved slots for solar photothermal conversion

Nanofluids are one of the keys to improving solar energy utilization efficiency. Metal nanoparticles (MNPs) have narrow-band absorption limitations in photothermal conversion. Recent studies have shown that it can overcome narrow-band absorption by adding slots on the nanoparticles (NPs) to improve photothermal conversion efficiency. In this work, we investigated the effect of curved slots on the optical properties of Ag nanorods by the finite element method. The results show that the presence of the curved slot enables the Ag nanorods to excite multiple resonance absorption peaks in the wavelength range of 300–1100 nm. The curved slotting reduces the overall scattering of the Ag nanorods and enhances its spectral absorption in the visible and near-infrared regions. In addition, we also calculated and compared the photothermal conversion efficiency of nanorods and nanorods with curved slots. At fv = 1 × 10−5 and h = 20 mm, the photothermal conversion efficiency of the curved slot Ag nanorods is increased by 6.8% over that of the Ag nanorods. In the measured volume fraction and fluid depth range, when the photothermal conversion efficiency reaches about 90%, the h and fv required for nanorods with curved slots are about 0.64 times that of nanorods. Nanorods with curved slots only need a meagre volume fraction and fluid depth to achieve high photothermal conversion efficiency. We believe that the proposed curved slot metal nanorods can provide a feasible solution for solving the narrow-band absorption of nanorods and improving the efficiency of solar energy utilization.

Light Induced Synthesis of Ag Nanorods for Potential Application as Optical Filter Tailored to Visible Domain

Monodispersed Ag nanorods were synthesized using a one-pot synthesis method. These Ag nanorods normally manifest dual surface plasmon resonance (SPR) peaks. This work presents a study of the variation of SPR peaks with variation in the shape of Ag nanorods. Shape variation was achieved through the degradation of a shape-controlling agent (PVP in this work) under white light irradiance with silica passivation to halt further shape variations. This paper also reports the growth & characterization of thin films of the synthesized rod-shaped silver nanoparticles on glass slides along with studies on band pass filter characteristics of the as-synthesized nanoparticles.

Facile Preparation of Monodisperse Silver Nanorods with Tunable Plasmon Resonances in the Near-Infrared Region: Implications for SERS-Based Sensing

The facile synthesis of silver nanorods with uniform size and tunable localized surface plasmon resonances is of great significance for plasmon resonance-related applications, such as surface-enhanced Raman spectroscopy (SERS)-based sensing, biomedical diagnostics, and photothermal therapy. However, improving reproducibility is difficult for nonexpert researchers since general synthesis methods involve multiple steps. Addressing this issue, this work develops a facile, effective synthetic strategy for monodisperse silver nanorods with tunable plasmon resonance in the near-infrared region assisted by in situ monitoring via an optical microfiber in the seed formation stage and surfactant-assisted purification of the final product. The optical microfiber monitoring ensures the formation of monodisperse bipyramid templates, guaranteeing the synthesis of the final product. The surfactant-assisted purification of the final product ensures the monodispersity of the final Ag nanorods. This study provides a flexible and alternative approach for nonexpert researchers and may present an opportunity for solving the reproducibility problem faced by nanomaterial synthesis.

Significantly boosted photoelectrochemical water splitting performance by plasmonic enhanced Hematite@MOF composite photoelectrodes

Hematite as a catalyst for photoelectrochemical water splitting offers huge potential, due to its high chemical stability, great abundance, and low cost. However, the low water oxidation kinetics and poor charge transportation have hindered progress towards the manufacture of practical water splitting devices. To tackle these problems, a visible light responsive metal-organic framework (MOF) polyhedral zeolitic imidazolate (ZIF-67), and optimised plasmonic Ag nanorods were incorporated into hematite nanostructures to form a three-component heterojunction photoelectrode. The designed photoanode showed dramatically improved light harvesting in the visible range and enhanced charge transport. A mechanistic investigation allowed the deconvolution of the enhanced performance pathways. First, the Hematite@ZIF-67 core-shell p-n junction enables facile charge carrier transfer between ZIF-67 and hematite. In addition, ZIF-67 also provides active sites for water oxidation and boosts surface oxygen evolution reaction (OER) kinetics. Guided by finite-difference time-domain (FDTD) modelling, Ag nanorods with optimised aspect ratio were incorporated between ZIF-67 and hematite. The Ag nanorods facilitate broadband light absorption and surface charge injection, induced by near-field excitation enhancement and plasmonic resonance energy transfer (PRET) pathways. The design and addition of ZIF-67 and Ag nanorods result in superior performance for a hematite-based photoanode for photoelectrochemical (PEC) water oxidation.

A SERS based clinical study on HIV-1 viral load quantification and determination of disease prognosis.

In resource limited settings, a cost-effective point-of-care diagnostic testing possessing the characteristics of detecting the minimum viral load of a malady like human immunodeficiency virus (HIV) acquired immune deficiency syndrome (AIDS) is a pressing priority. The present work describes a novel, rapid and field-deployable method using surface enhanced Raman spectroscopy (SERS) for detection and prognosis of HIV positive clinical samples, in seven different viral load ranges varying between 200 and 1 million copies/ml. A relationship between the increasing and decreasing intensity peaks of HIV-1 was also established for quantitation efficacy of the handheld tool. Three different types of SERS substrates: single arm Ag nanorods, double arm Ag nanorods and Au sputtered single arm Ag nanorods were used and the obtained data was compared for the three substrates. It was demonstrated that maximum enhancement was obtained for Au sputtered Ag nanorods. Rigorous coupled wave analysis (RCWA) simulations were performed to study the 'hotspots' in three different SERS substrates. Further, to explore the utility of our platform and to differentiate between the clade specific X4 and R5 tropism, their corresponding SERS spectra were studied using HIV-1 strains belonging to four different HIV-1 subtypes (A, B, C and D) which showed a clear distinction, implying the usefulness of the platform in understanding the disease prognosis. Statistical analysis of the obtained SERS spectra using principal component analysis (PCA) showed good agreement with the experimental results, confirming the ability of SERS platform to quantitate HIV-1 viral load and distinguish HIV-1 strains on the basis of their SERS spectra.