Luminescence Enhancement and SERS by Self-Assembled Plasmonic Silver Nanostructures in Nanoporous Glasses

It was shown experimentally that the action of continuous electric field on nanoporous silicate glasses with interconnecting pores, containing silver nanoparticles, leads to the spatial redistribution of nanoparticles. The concentration of nanoparticles near the negative electrode increases and results in silver nano- and microdendrite structure growth. The main mechanisms of the described effects are the field emission of silver ions from silver nanoparticles near negative electrode, migration of silver ions in the external electric field to the negative electrode, reduction of silver ions by free electrons, and new silver nanoparticle formation. The experiments have shown that at the ends of microdendrites, local field enhancement appears, which results in luminescence enhancement and in SERS.

     

金溶胶基底的 SERS 增强效果的实验研究

本文以结晶紫作为探针分子,研究了以金溶胶膜、pH ＝6以及 pH ＝13的金溶胶溶液为活性基底的表面增强拉曼光谱的增强效果。采用化学还原法制备金溶胶,加入氢氧化钠改变其 pH 值,并以自组装法制备金溶胶膜。通过比较金溶胶膜、pH ＝6及 pH ＝13时金溶胶溶液的增强因子以及在这三种金溶胶基底上结晶紫的检测限,分析不同活性基底增强效果的差异。三种活性基底的增强因子分别可达到5．9×103、1．5×105、2．3×107,pH ＝13的金溶胶溶液有最佳的增强效果。以这三种金溶胶为基底对结晶紫进行表面增强拉曼光谱探测,可得到检测限为70．7 nmol／L、9．6 nmol／L、1．8 nmol／L。结果表明,金溶胶溶液的增强效果明显优于金溶胶膜,而通过改变金溶胶体系的 pH 值可以改变金纳米颗粒的聚合程度及对探测物的吸附特性从而获得更高灵敏度的活性基底。     

Obtain Quadruple Intense Plasmonic Resonances from Multilayered Gold Nanoshells by Silver Coating: Application in Multiplex Sensing

Four intense and separate localized surface plasmon resonance (LSPR) absorption peaks have been obtained in the gold-dielectric–gold–silver multilayer nanoshells. The silver coating on the gold shell results in a new LSPR peak at about 400 nm corresponding to the $ {{\left| {\omega_{+}^{-}} \right\rangle}_{Ag }} $ mode. The intense local electric field concentrated in the silver shell at the wavelength of 400 nm indicates that this new plasmonic band is coming from the symmetric coupling between the antibonding silver shell plasmon mode and the inner sphere plasmon. Increasing the silver shell thickness also leads to the intensity increasing of the $ {{\left| {\omega_{+}^{-}} \right\rangle}_{Au }} $ mode and blue shift of $ \left| {\omega_{-}^{+}} \right\rangle $ and $ \left| {\omega_{-}^{-}} \right\rangle $ modes. Therefore, quadruple intense plasmonic resonances in the visible region could be achieved in gold-dielectric–gold–silver multilayer nanoshells by tuning the geometrical parameters. And the quadruple intense plasmonic resonances in the visible region provide well potential for multiplex biosensing based on LSPR.     

Features of the Secondary Emission Enhancement Near Plasmonic Gold Film

Plasmonic gold films (PGF) prepared by vacuum deposition of gold onto quartz slides possess unique property to enhance electromagnetic signal in the near field. Spectral tuning of PGF’s plasmon band to resonance with the electronic spectra of adsorbed molecules provides selective enhancement of fluorescence or surface-enhanced Raman scattering in the far field. Plasmon-enhanced fluorescence (PEF) of mitoxantrone (mitox) as a function of the distance between gold surface and adsorbed molecules for different polarization and incidence angle of exciting light is analyzed in this work. Spectrophotometric data reveal that probability of localized plasmon excitation in gold grains increases with growth of incidence angle for s-polarized and decrease for p-polarized excitation. This fact correlates well with oblate shape of gold particles detected by Atomic force microscope. However, the fluorescence intensity of dyes deposited at fixed distance from gold surface increase with angle of incidence of p-polarized light more noticeably than for s-polarized one. Nevertheless, the behavior of mitox PEF signal upon p-polarized laser excitation and different angle of incidence are similar in appearance to such phenomenon as selective photoelectric effect. According to this observation, the near-field interactions between plasmons and molecule as possible mechanism of PEF is discussed.     

Plasmonic Enhancement of Dye Sensitized Solar Cells via a Tailored Size-Distribution of Chemically Functionalized Gold Nanoparticles

A substantial and stable increase of the current density J_sc of ruthenium (Ru) dye sensitized solar cells (DSC) of up to 16.18% and of the power efficiency of up to 25.5% is demonstrated in this article via plasmonic enhancement. The key aspect of this work is the use of a tailored bimodal size distribution of functionalized gold nanoparticles (AuNPs) that have been chemically immobilized onto the mesoporous titanium dioxide (TiO₂) layer via short, stable dithiodibutyric acid linkers. The size distribution of the AuNPs is a result of theoretical calculations that aimed at the perfection of the absorption characteristics of the complete solar cell system over a wide range of wavelengths. The functionalization of the AuNPs serves to bind them at a close but defined distance to TiO₂-particles and additionally to chemically protect them against potential corrosion by the electrolyte. Simulations of near field (enhanced absorption) and far field (scattering) contributions have been used to tailor a complex AuNPs bimodal size distribution that had subsequently demonstrated experimentally a close to optimum improvement of the absorbance over a wide wavelength range (500–675 nm) and therefore an impressive DSC efficiency enhancement. Finally, the modified DSCs are exhibiting pronounced longevity and stable performance as confirmed via long time measurements. In summary, the presented systems show increased performance compared to non plasmonic enhanced cells with otherwise identical composition, and are demonstrating a previously unpublished longevity for iodide electrolyte/AuNPs combinations.     

Contrast Enhancement in Fluorescence Microscope by Plasmonic Coupling

A fluorescence microscope taking advantage of plasmonic coupling is in-proof demonstrated. Silver nano-wires and nano-particles are chosen as the metallic nano-objects, which are put on a silver film with the Rhodamine B-doped PMMA film as the spacer. Plasmonic coupling between the metallic nano-objects and the Ag film will induce either fluorescence quenching or enhancement dependent on the thickness of the spacer layer, which both enhance the contrast of the fluorescence images. Our experiment provides a feasible method to enhance the contrast of fluorescence microscope, which has potential applications in fluorescence-based imaging or sensing.     

Protein-Metal Interactions Probed by SERS: Lysozyme on Nanostructured Gold Surface

Plasmonics - Surface-enhanced Raman scattering is a well-established technique for molecular detection at low concentration, which is becoming increasingly popular in the field of biotechnology and...     

Broadband Enhancement of PbS Quantum Dot Solar Cells by the Synergistic Effect of Plasmonic Gold Nanobipyramids and Nanospheres

For the first time, the plasmonic gold bipyramids (Au BPs) are introduced to the PbS colloidal quantum dot (CQD) solar cells for improved infrared light harvesting. The localized surface plasmon resonance peaks of Au BPs matches perfectly with the absorption peaks of conventional PbS CQDs. Owing to the geometrical novelty of Au BPs, they exhibit significantly stronger far‐field scattering effect and near‐field enhancement than conventional plasmonic Au nanospheres (NSs). Consequently, device open‐circuit voltage (V_oc) and short‐circuit current (J_sc) are simultaneously enhanced, while plasmonic photovoltaic devices based on Au NSs only achieve improved J_sc. The different effects and working mechanisms of these two Au nanoparticles are systematically investigated. Moreover, to realize effective broadband light harvesting, Au BPs and Au NSs are used together to simultaneously enhance the device optical and electrical properties. As a result, a significantly increased power conversion efficiency (PCE) of 9.58% is obtained compared to the PCE of 8.09% for the control devices due to the synergistic effect of the two plasmonic Au nanoparticles. Thus, this work reveals the intriguing plasmonic effect of Au BPs in CQD solar cells and may provide insight into the future plasmonic enhancement for solution‐processed new‐generation solar cells.     

Tuning Plasmonic Properties of Truncated Gold Nanospheres by Coating

The influence of TiO₂ coating on resonant properties of gold nanoisland films deposited on silica substrates was studied numerically and in experiments. The model describing plasmonic properties of a metal truncated nanosphere placed on a substrate and covered by a thin dielectric layer has been developed. The model allows calculating a particle polarizability spectrum and, respectively, its surface plasmon resonance (SPR) wavelength for any given cover thickness, particle radius and truncation parameter, and dielectric functions of the particle, the substrate, the coating layer, and the surrounding medium. Dependence of the SPR position calculated for truncated gold nanospheres has coincided with the measured one for the gold nanoisland films covered with titania of different thicknesses. In the experiments, gold films with thickness of 5 nm were deposited on a silica glass substrate, annealed at 500 °C to form nanoislands of 20 nm in diameter, and covered with amorphous titania layers using atomic layer deposition technique. The resulting structures were characterized with scanning electron microscopy and optical absorption spectroscopy. The measured dependence of the SPR position on titania film thickness corresponded to the one calculated for truncated sphere-shaped nanoparticles with the truncation angle of ~50°. We demonstrated the possibility of tuning the SPR position within ~100 nm range by depositing to 30 nm thick titania layer.

     

Field Enhancement by Shaping Nanocavities in a Gold Film

We report on 2D plasmonic crystals composed of a hexagonal lattice of polymeric nanopillars embedded in an optically thick gold film on a glass substrate. A tapered shape of the polymeric pillars is proved to localize the electric field distribution close to the free surface of the device and to determine a significant increase in the electric field intensity particularly when the incident light comes from the glass side. These effects significantly improve the sample sensitivity to a refractive index change occurring at the free surface of the device.     

High-Performance Enhancement of a GaAs Photodetector Using a Plasmonic Grating

Plasmonics - In this study, we present and establish a gold surface plasmon polariton (SPP) GaAs photodetector that achieves high internal quantum efficiency (IQE). At a wavelength of...     

Plasmonic Enhancement of Fluorescence and Raman Scattering by Metal Nanotips

We report modifications to the optical properties of fluorophores in the vicinity of noble metal nanotips. The fluorescence from small clusters of quantum dots has been imaged using an apertureless scanning near-field optical microscope. When a sharp gold tip is brought close to the sample surface, a strong distance-dependent enhancement of the quantum dot fluorescence is observed, leading to a simultaneous increase in optical resolution. These results are consistent with simulations of the electric field and fluorescence enhancement near plasmonic nanostructures. Highly ordered periodic arrays of silver nanotips have been fabricated by nanosphere lithography. Using fluorescence lifetime imaging microscopy, we have created high-resolution spatial maps of the lifetime components of vicinal fluorophores; these show an order of magnitude increase in decay rate from a localized volume around the nanotips, resulting in a commensurate enhancement in the fluorescence emission intensity. Spatial maps of the Raman scattering signal from molecules on the nanotips shows an enhancement of more than five orders of magnitude.     

Application of Gold Nanorods for Plasmonic and Magnetic Imaging of Cancer Cells

We report the use of biocompatible gold nanorods (GNRs) as multimodal (plasmonic and magnetic) probes for cancer cell labeling in vitro. These multifunctional and multimodal bioconjugates were prepared by replacing cetyltrimethylammonium bromide with a mixture of functionalized PEGylation molecules so that a variety of functionalities (e.g., magnetic resonance imaging agent gadolinium (Gd) and biorecognition molecule transferrin (Tf)) can be easily integrated using simple chemistry. It was shown that Gd incorporation did not interfere with the plasmonic properties of the GNRs and a strong T1 relaxivity was estimated (10.0 mM⁻¹ s⁻¹), which is more than twice that of the clinical MRI agent Gd-DTPA. The large observed T1 relaxivity was possibly due to the huge surface to volume ratio of GNR, which allowed huge amount of amine-terminated molecule to anchor on the surface, coupled with Gd (III) ions for the enhanced relaxation of water protons. Pancreatic cancer cell overexpressing the transferring receptor was served as the in vitro model, and the Tf-mediated uptake was demonstrated and confirmed by dark-field imaging and transmission electron microscopy. More importantly, cell viability (MTS) assay did not reveal any sign of toxicity in these treated cells, suggesting that PEGylated GNRs can serve as a biocompatible, multifunctional, and multimodal platform for variable bio-applications.     

Plasmonic Micro-Antenna Characteristics Using Gold Grating Embedded in a Panda-Ring Circuit

Plasmonics - An investigation of the plasmonic micro-antenna characteristics using an optical modified add–drop multiplexer embedded gold grating is proposed. A device consisting of a main...     

Resonant Broadband Field Enhancement in Cylindrical Plasmonic Structure Surrounded by Perovskite Environment

We demonstrate the optical response of metal nanoparticles and their interaction with organic-inorganic perovskite (methyl ammonia lead halide (CH₃NH₃PbI₃)) environment using discrete dipole approximation (DDA) simulation technique. Important optical properties like absorption, scattering, and electric field calculations for metal nanoparticle using different geometry have been analyzed. The metal nanoparticles embedded in the perovskite media strongly support surface plasmon resonances (SPRs). The plasmonic interaction of metal nanoparticles with perovskite matrix is a strong function of MNP’s shape, size, and surrounding environment that can manipulate the optical properties considerably. The cylindrical shape of MNPs embedded in perovskite environment supports the SPR which is highly tunable to subwavelength range of 400–800 nm. Wide range of particle sizes has been selected for Ag, Au, and Al spherical and cylindrical nanostructures surrounded by perovskite matrix for simulation. The chosen hybrid material and anisotropy of structure together make a complex function for resonance shape and width. Among all MNPs, 70-nm spherical silver nanoparticle (NP) and cylindrical Ag NP having diameter of 50 nm and length of 70 nm (aspect ratio 1.4) generate strong electric field intensity that facilitates increased photon absorption. The plasmonic perovskite interaction plays an important role to improve the absorption of photon inside the thin film perovskite environment that may be applicable to photovoltaics and photonics.

     

Resonant TE Transmission Through a Continuous Metal Film: Perspectives for Low-Loss Plasmonic Elements

Whereas resonant transverse magnetic transmission across an undulated continuous metal film is achieved with the mediation of plasmon modes excited by the undulation, it is shown here that transverse electric (TE) resonant transmission through a continuous metal film can also be achieved with the mediation of the second-order TE₁ mode of a dielectric slab waveguide having the metal film sandwiched at its middle. The demonstration is made by using the materials currently used in the domain of optical security and counterfeit deterrence: ZnS is shown to possibly be a lossless interface/adhesion layer between a polymer and a noble metal for plasmonic resonant elements.     

Controlled In Situ Seed-Mediated Growth of Gold and Silver Nanoparticles on an Optical Fiber Platform for Plasmonic Sensing Applications

Plasmonics - This study presents an in situ growth technique to develop highly sensitive plasmonic fiber optic sensors with an excellent control over the plasmonic properties of gold (AuNPs) and...     

Utilizing the Metallic Nano-Rods in Hexagonal Configuration to Enhance Sensitivity of the Plasmonic Racetrack Resonator in Sensing Application

A high sensitive plasmonic refractive index sensor based on metal-insulator-metal (MIM) waveguides with embedding metallic nano-rods in racetrack resonator has been proposed. The refractive index changes of the dielectric material inside the resonator together with temperature changes can be acquired from the detection of the resonance wavelength, based on their linear relationship. With optimum design and considering a tradeoff among detected power, structure size, and sensitivity, the finite difference time domain simulations show that the refractive index and temperature sensitivity values can be obtained as high as 2610 nm per refractive index unit (RIU) and 1.03 nm/°C, respectively. In addition, resonance wavelengths of resonator are obtained experimentally by using the resonant conditions. The effects of nano-rods radius and refractive index of racetrack resonator are studied on the sensing spectra, as well. The proposed structure with such high sensitivity will be useful in optical communications that can provide a new possibility for designing compact and high-performance plasmonic devices.     

Fabrication Friendly Plasmonic Metasurface Sensing and Switching Configuration Based on Plasmonic Induced Absorption: Analytical and Numerical Evaluation

Plasmonics - Optical sensing and switching characteristic for a novel plasmonic metasurface structure are verified based on numerical and analytical evaluations for the proposed structure formed by...