Synthesis of Peptide Mediated Au Core–Ag Shell Nanoparticles as Surface-Enhanced Raman Scattering Labels

As the fundamental understanding of metal–light interactions gains solid grounds, further research has been devoted to construct novel structures that take full advantage of such unique interactions, which is called plasmonics. In this report, the preparation of Au–Ag core–shell structures obtained by coating the Au surface with peptide and Raman reporter molecule and depositing an Ag layer on it is reported. The prepared Au–Ag NPs are tested for their surface-enhanced Raman scattering (SERS) performance. The negatively charged peptides with three different lengths, which are 3 (P1), 15 (P2), and 21 (P3) amino acid long, were chemically attached to 13 nm AuNPs along with Raman reporter molecule, carboxytetramethylrhodamine, and these modified AuNPs were coated with three different shell thickness of Ag metal. The prepared Au–Ag NPs were tested for their SERS performance and found that the Au–Ag NPs prepared with P2 and thickest shell performs best as SERS label.     

Importance of Metal–Adsorbate Interactions for the Surface-enhanced Raman Scattering of Molecules Adsorbed on Plasmonic Nanoparticles

The interaction between adsorbates of different nature and plasmonic nanoparticles is reviewed here on the basis of the work done in our laboratory in the past few years. The paper is structured for analyzing the interaction of adsorbates with metal nanoparticles as function of the interacting atom (O, N, or S) and the adsorbate conformation. In the study of the adsorption of molecular species on metals, it is necessary to take into account that different interaction mechanisms are possible, leading to the existence of different molecular forms (isomers or conformers). These forms can be evidenced by changing the excitation wavelength, due to a resonant selection of these wavelengths. Charge-transfer complexes and electrostatic interactions are the usual driving forces involved in the interaction of adsorbates on metal surfaces when these metallic systems are used in wet conditions. The understanding of the metal–adsorbate interaction is crucial in the surface functionalization of metal surfaces, which has a growing importance in the development of sensing systems or optoelectronic devices. In relation to this, special attention is paid in this work to the study of the adsorption of calixarene host molecules on plasmonic nanoparticles.     

The Effect of Negative Curvature on the Plasmonic Coupling of Concentric Core–Shell Metallic Nanostructures

Negative curvature-dependent localized surface plasmon resonance (LSPR) properties of concentric core–shell metallic nanostructure have been studied using quasistatic approach and plasmon hybridization theory. Whether in single-layered gold nanoshell or double gold nanoshells, the oscillating surface charges always concentrate close to the poles of the metal surface with negative curvature, which results in the anisotropic local electric field distribution and affects both the inter-surface plasmonic coupling and inter-shell plasmonic coupling. Therefore, the change of the radius of the gold surface with negative curvature could modulate the plasmon hybridization and lead to the LSPR shifting. The physical mechanism of the negative curvature-dependent LSPR presents a potential for design and fabrication of nanoscale optical device based on core–shell type metallic nanostructures.     

Plasmonic Effect Enhancement in Ridge–Trench Structure Assisted by Fluorescence Dye

Confinement of exciton–polaritons using ridge–trench structures filled with fluorescent dye materials was investigated on the basis of geometrical analysis as well as plasmonic behavior analysis. It was found that the photoluminescence intensity of the dye increased significantly in the trench than on the ridge due to geometry confinement. However, with silver layer deposited between the ridge–trench structure on Si substrate and the fluorescence dye, apparent photoluminescence peaks due to surface plasmon resonance centered at 360 nm (3.45 eV) were generated while the photoluminescence peaks of the dye materials centered at 580 nm (2.14 eV) quenched in the trench. Competition of spontaneous emission coupled into external electromagnetic modes and plasmon modes is the cause for the quench in photoluminescence. Our results show a direct energy transfer from low-energy photoluminescence to higher energy photoluminesence in dye materials due to plasmonic resonance effects.     

Plasmonic, Low-Frequency Raman, and Nonlinear Optical-Limiting Studies in Copper–Silica Nanocomposites

Nanocomposite thin films consisting of Cu nanoparticles embedded in silica matrix were synthesized by atom beam co-sputtering technique. Plasmonic, optical, and structural properties of the nanocomposite films were investigated by using ultraviolet (UV)–visible absorption spectroscopy, nonlinear optical transmission, X-ray diffraction (XRD), and low-frequency Raman scattering. UV–visible absorption studies revealed the surface plasmon resonance absorption at 564 nm which showed a red shift with increase in Cu fraction. XRD results together with surface plasmon resonance absorption confirmed the presence of Cu nanoparticles of different size. Low-frequency Raman studies of nanocomposite films revealed breathing modes in Cu nanoparticles. Nanocomposites with lower metal fractions were found to behave like optical limiters. The possibility of controllably tuning the optical nonlinearity of these nanocomposites could enable them to be the potential candidates for applications in nanophotonics.     

Narrowband Light Total Antireflection and Absorption in Metal Film–Array Structures by Plasmonic Near-Field Coupling

We study the cooperative effects between plasmon gap modes and optical cavity modes of a novel triple-layer structure consisting of double continuous gold films separated by a gold nanosphere array. Narrowband near-perfect antireflection of optical field is achieved for the first time due to the strong near-field light–matter interaction within the deep sub-wavelength gaps between adjacent nanospheres combined with the spatial field confinement effects of the optical cavity built by the double gold films. The coexistence cooperation of near-field dipole plasmon resonances and spatial optical field confinement presents more efficient light modification than that of the individual subsystem and may open a new approach to manage light flow. By varying the period of nanosphere array, the diameter of nanospheres, and the distance between the array and the film, optical behaviors of the proposed structure can be tuned in a wide range. High environmental sensitivity and large figure of merit factor are obtained using this structure as the detecting substrate. Furthermore, ultra-compact structure and high conduction suggest the proposed structure being a good candidate for potential applications in highly integrated optoelectronic devices, such as plasmonic filters and sensors.     

Farfield Under Small Scattering Angle in the Rectangular Ag–Si–SiO2 Cavity

Plasmonics - In this paper, the farfield under small scattering angle was investigated in the rectangular Ag–Si–SiO2 cavity by FDTD. The simulation results showed that Re(E) of the...     

Plasmonic Core–Shell Nanowires for Enhanced Second-Harmonic Generation

We demonstrate the synthesis and characterization of core–shell nanowires consisting of a non-centrosymmetric KNbO₃ core and a gold shell. This type of nanostructure combines the nonlinear optical properties of the core and the plasmonic resonance of the shell in the near infrared spectral range. We report successful spectroscopic measurements on coated single wires to characterize the resonant behavior of the gold shell. We present a theoretical model based on the electrostatic approximation to estimate the enhancement of second-harmonic generation in a nanowire due to the shell. It suggests a possible enhancement factor of up to 4,000 for a system with a nanoshell of 16 nm thickness at a wavelength of 900 nm.     

Event-related Potentials in Audio–Visual Cross-Modal Test for Comparison of Word Pairs

Human Physiology - The study was aimed at investigating specificities of brain functioning when comparing verbal signals in cross-modal interaction. Event-related potentials (ERPs) were recorded in...     

The Periodically Graded Metal–Insulator–Metal Gap Structure for Plasmonic Waveguides

In this paper, we explore the potential of the plasmonic metal–insulator–metal (MIM) periodically graded structure. Based on the coupled modes approach, an analytical model has been observed for the surface plasmon polariton (SPP) propagation. The band modes of SPP can be also supported by the MIM structure and we have analyzed the strong dependence of band width on structure parameters. The obtained analytical expressions allow one to easily choose the structure parameters for the desired band width.     

A Highly Sensitive Resonance Scattering Assay for Immunoglobulin M Using Ag(I)–Hydroquinone–Immunonanogold Catalytic Reaction

Ten-nanometer nanogold showed the strongest catalytic effect on the particle reaction between Ag(I) and hydroquinone to form nanosilver particles that exhibited the strongest resonance scattering (RS) peak at 350 nm. The enhanced RS intensity was linear to the nanogold concentration in the range of 30–5,700 nM Au. The nanogold was used to label goat antihuman immunoglobulin M (GIgM) to obtain an immunonanogold probe (AuGIgM) for immunoglobulin M (IgM). Based on the nanogold-labeled immunoreaction between IgM and AuGIgM, centrifugation, and AuGIgM–Ag(I)–hydroquinone nanocatalytic reaction, a highly sensitive and selective immunonanogold-catalytic Ag particle RS assay for 0.2–300 ng mL^?1 IgM was proposed, with a detection limit of 0.1 ng mL^?1. This assay was simple and sensitive and was applied to assay IgM in serum samples, with satisfactory results.     

Noble Metal Ion Embedded Nanocomposite Glass Materials for Optical Functionality of UV–Visible Surface Plasmon Resonance (SPR) Surface-Enhanced Raman Scattering (SERS) X-ray and Electron Microscopic Studies: An Overview

Plasmonics - Raman spectroscopy (RS) is a modern scientific analytic fingerprint technique that detects, examines, and analyzes the constituent chemical composition of various substances...     

SiO2–Silver Metasurface Architectures for Ultrasensitive and Tunable Plasmonic Biosensing

Plasmonics - Here, we indicate that metasurface-based biosensors consisting of silver-metasurface with SiO2 and working in the near-infrared (NIR) spectral range can obtain simultaneous...     

Plasmonic Photonic Bloch Oscillations in Composite Metal–Insulator–Metal Waveguide Structure

This study proposes the time-evolved plasmonic photonic Bloch oscillations (PBOs) in a composite metal–insulator–metal (CMIM) waveguide structure. This device contains two kinds of MIM waveguide with different thickness of the insulator gaps. The time-resolved plasmonic PBO motion in this CMIM waveguide can be observed by introducing a linearly graded dielectric material. The ray trajectory results from the Hamiltonian optics are consistent with the finite-difference time-domain simulation results.     

Characteristics of Malignant Tumors in 230 Husband–Wife Pairs

The aim of this study is to obtain a reference point for early detection of tumors in individuals whose spouses were diagnosed with malignant tumors. Data from 230 husband and wife pairs with malignant tumors were collected and analyzed from the family history records of 15,000 people who came to the Department of Cancer Prevention, Cancer Institute/Hospital, Chinese Academy of Medical Sciences for cancer screening between January 2009 and May 2012. The median diagnosis age was 67 years for husbands and 65 years for wives. A total of 214 cases (46.5 %) had digestive system malignancies. Respiratory system cancers were diagnosed in 64 husbands, of whom 20 (31.3 %) had spouses also with respiratory system cancer. Lung cancer ranked first for the females. The total number of lung cancer and commonly seen female-specific cancers (breast, ovarian, uterine, and cervical) was 127 (55.2 %). The difference in age at diagnosis between spouses was less than 10 years in 134 couples (58.3 %), while 77 (33.5 %) couples had an age difference less than 5 years. A family history of malignant tumors in first-degree relatives was documented in 48.3 % of the husbands and 48.7 % of the wives. The occurrence of cancer in both spouses of the couples studied resulted from an interaction between genetic and environmental factors. Nonhereditary factors such as diet, smoking, passive smoking, and air pollution also contributed to the development of cancers. It is recommended that when husband is diagnosed with cancer, the wife should be screened focusing on lung, breast, and gynecological cancers. If the wife was diagnosed with malignant disease, then screening for lung and digestive system cancers should be emphasized in the husband.     

Speckled SiO2@Au Core–Shell Particles as Surface Enhanced Raman Scattering Probes

Silica particles of ~800 nm size were functionalized using 3-amino propyl triethoxysilane molecules on which gold particles (~20 nm size) were deposited. The resulting particles appeared to form speckled SiO₂@Au core–shell particles. The surface roughness, along with hot spots, due to nanogaps between the gold nanoparticles was responsible for the enhancement of the Raman signal of crystal violet molecules by ~3.2?×?10⁷ and by ~1.42?×?10⁸ of single-wall carbon nanotubes. It has also been observed that the electromagnetic excitation near surface plasmon resonance (SPR) of core–shell particles is more effective than off resonance SPR excitation.     

An Affinity–Effect Relationship for Microbial Communities in Plant–Soil Feedback Loops

Feedback loops involving soil microorganisms can regulate plant populations. Here, we hypothesize that microorganisms are most likely to play a role in plant–soil feedback loops when they possess an affinity for a particular plant and the capacity to consistently affect the growth of that plant for good or ill. We characterized microbial communities using whole-community DNA fingerprinting from multiple "home-and-away" experiments involving giant ragweed (Ambrosia trifida L.) and common sunflower (Helianthus annuus L.), and we looked for affinity–effect relationships in these microbial communities. Using canonical ordination and partial least squares regression, we developed indices expressing each microorganism's affinity for ragweed or sunflower and its putative effect on plant biomass, and we used linear regression to analyze the relationship between microbial affinity and effect. Significant linear affinity–effect relationships were found in 75 % of cases. Affinity–effect relationships were stronger for ragweed than for sunflower, and ragweed affinity–effect relationships showed consistent potential for negative feedback loops. The ragweed feedback relationships indicated the potential involvement of multiple microbial taxa, resulting in strong, consistent affinity–effect relationships in spite of large-scale microbial variability between trials. In contrast, sunflower plant–soil feedback may involve just a few key players, making it more sensitive to underlying microbial variation. We propose that affinity–effect relationship can be used to determine key microbial players in plant–soil feedback against a low "signal-to-noise" background of complex microbial datasets.     

Optical Magnetic Resonances in Subwavelength Ag–MgF2–Ag Grating Structures

Optical magnetic responses were demonstrated in subwavelength Ag–MgF₂–Ag grating structures for transverse magnetic-polarized light. The subwavelength Ag–MgF₂–Ag grating structures were fabricated using e-beam lithography followed by a lift-off process. By fixing the Ag–MgF₂–Ag strip dimension, the effect of the stripe width on the magnetic resonances was compared for two different grating pitches. With further reduced grating pitch, we pushed the optical magnetic resonances to near UV (deep blue). Numerical simulations confirmed our experimental observations and were in good agreement with the experimental results.     

Near-infrared Plasmonic Far-field Nanofocusing Effects with Elongated Depth of Focus based on Hybrid Au–Dielectric–Ag Subwavelength Structures

In this paper, we propose a new far-field nanofocusing lens with elongated depth of focus (DOF) under near-infrared (NIR) wavelength. The surface plasmons can be excited by using the hybrid metal–insulator–metal (MIM) subwavelength structure under the NIR wavelength. The constructive interference of surface plasmons launched by the subwavelength MIM structure can form a nanoscale focus that is modulated by the novel metal grating from the near field to the far field. The numerical simulations demonstrated that a nanoscale focal spot (in plane focal area 0.177λ ²) with elongated DOF (3.358λ) and long focal length (5.084λ) can be realized with reasonably designing parameters of the lens. By controlling the positions of the inner radii of each slit ring and the grating width, the focal length, focal spot, and DOF can be tuned easily. This design method, which can obtain the nanoscale focal spot and micron DOF in far field under NIR illumination, paved the road for utilizing the NIR plasmonic lens in superresolution optical microscopic imaging, optical trapping, biosensing, and complex wavefront/beam shaper.