Multiple Surface Plasmon Resonances Research Articles

Photochemical Synthesis of Sericin-Coated Gold Nanorods and Their Antibacterial Activity under Low-Level Near-Infrared Light.

Gold nanorods (GNRs) are unique nanoparticles with easily functionalized surfaces, multiple synthesis methods, photothermal conversion, and surface plasmon resonance effects. These properties make GNRs suitable for various biological applications. However, a rapid synthesis of GNRs using less toxic chemicals is needed. The photochemical method is a viable option that can synthesize GNRs quickly while using fewer chemicals. A photochemical method is reported for the synthesis of GNRs using Irgacure-2959 as a reducing agent. This method could be used to synthesize GNRs with a rod-like shape within 30 min. Additionally, GNRs were coated with sericin (GNRs-SC) to further reduce their toxicity in human dermal fibroblast adult cells. Low-level near-infrared (NIR) light was applied to enhance the photothermal therapy of both GNRs and GNRs-SC. The results showed that GNRs and GNRs-SC under low-level NIR light have enhanced antibacterial activity against Staphylococcus aureus and Escherichia coli, as well as antibiofilm activity against S. aureus. Furthermore, GNRs-SC showed good biocompatibility with antibacterial and antibiofilm activities. These results indicate that GNRs-SC are good candidates for various biological applications.

Biomimetic synthesis and use of silver nanoparticles, an innocuous stratagem to combat fungal diseases in plants

In the era of antimicrobial resistance, the creation of novel nanoparticles with resilient antimicrobial activity and the need to progress a comprehensive approach to fight pathogenic fungi is critical. Due to the immense range of variations of Calotropis procera phytochemicals, their versatile functionalization, and the possibility of multivalent binding sites make it preeminent for use in the present research to synthesize antifungal silver nanoparticles (AgNPs). The UV–visible (UV–vis) spectrum of AgNPs displayed the multiple Surface Plasmon Resonance (SPR) peaks with ʎMax 350 nm, 408 nm, 584 nm, 635 nm and 654 nm and sweeping change in spectrum revealed shape anisotropy. The multifunctional moieties of phytochemicals explored with Fourier Transform Infra-Red (FTIR) spectrum showed SO, PO, NH, OH and CO functional groups involved in a redox reaction that served as capping/stabilizing agents for created amphiphilic colloidal AgNPs structures. The X-ray diffraction (XRD) analysis revealed Face Centered Cubic (FCC) shaped Nano-sized silver. The Atomic Force Microscopy (AFM) analysis displayed predominant prism shape AgNPs with different size collections having a mean size of 28.8 nm. The significant in vitro antifungal activity against plant and human pathogenic fungus Scopulariopsis alboflavescens was observed using the disk diffusion method, and it was resolved that biogenic synthesis of AgNPs from plants will be a safe strategy to combat fungal diseases in plants.

Polarization- and angle-insensitive broadband long wavelength infrared absorber based on coplanar four-sized resonators.

In many potential applications, there is a high demand for long wavelength infrared (LWIR) absorbers characterized by a compact configuration, broad operational bandwidth, high absorption efficiency, and polarization- and angle-insensitive characteristics. In this study, we design and demonstrate a high-performance broadband LWIR absorber based on coplanar four-sized resonators, consisting of arrays of titanium (Ti) disks with different diameters supported by a continuous zinc selenide (ZnSe) layer and by a Ti film acting as a back-reflector. Particle swarm optimization (PSO) is employed to optimize the complicated geometry parameters, and the final optimized device exhibits near-unity absorption (∼96.7%) across the entire operational bandwidth (8 µm∼14 µm) under unpolarized normal incidence, benefiting from the impedance-matching condition and the multiple surface plasmon resonances of this configuration. Furthermore, the proposed absorber is insensitive to the angle of incidence due to the localized surface plasmon resonances supported by these four-sized resonators, and is insensitive to the state of polarization thanks to the highly symmetric feature of the circular pattern. The measured absorption of the fabricated sample exhibits a relatively high coincidence with the simulation, with an average absorption of 88.9% ranging from 8 µm to 14 µm. The proposed absorber, which can be easily integrated into a standardized micro/nano manufacture process for cost-effective large-scale production, provides a feasible solution for improving optical performance in thermal emitter, infrared detection, and imaging applications. Furthermore, the generalized design principle employing the optimized method opens up new avenues for realizing target absorption, reflection, and transmission based on more complicated structure configurations.

Multiple protein-patterned surface plasmon resonance biochip for the detection of human immunoglobulin-G.

A portable surface plasmon resonance (SPR) measurement prototype integrated with a multiple protein-patterned SPR biochip is introduced for label-free and selective detection of human immunoglobulin-G (H-IgG). The polyclonal anti-H-IgG antibodies derived from goat, rabbit, and mouse were immobilized through polydimethylsiloxane (PDMS) microchannels to fabricate the patterned SPR biochip. The PDMS surface was functionalized using 3-aminopropyltrimethoxysilane and bonded to carbodiimide-activated gold substrates to construct irreversibly bonded hydrophilic microfluidic chip at room temperature. For SPR measurement, a custom-made system is developed with a high angular scanning accuracy of 0.005° and a wide scanning range of 30°-80° that avoids the conventional requirement of expensive goniometric stages and detector arrays. The SPR biochip immobilized with 750μg/mL goat anti-H-IgG demonstrated detection of H-IgG with a detection limits of 15 μg/mL, and linear response through a wide concentration range (15-225 μg/mL) of high coefficient of determination (R2 =0.99661). The selectivity of the sensor was investigated by exposing them to two different non-specific targets (bovine serum albumin and polyvalent antivenom). The results indicate negligible sensor response towards nonspecific targets (0.25° for 30 μg/mL bovine serum albumin (BSA) and 0.25° for 30 μg/mL polyvalent antivenom) in comparison to H-IgG (1.5° for 30 μg/mL).

On-Fiber Multiparameter Sensor Based on Guided-Wave Surface Plasmon Resonances

We report an ultracompact on-fiber multiparameter sensor that employs multiple guided-wave surface plasmon resonances (GWSPRs) and machine learning based signal processing. The sensor structure entails a gold plasmonic crystal cavity covered with a planar dielectric waveguide on the end-face of a single-mode fiber. Incident light on the gold gratings of the plasmonic crystal cavity excites surface plasmon resonances, which are coupled into the waveguide and induce multiple, high-Q GWSPRs. Due to the difference in the field distributions of these resonance modes, the resonance dips in the sensor reflection spectrum have distinctive responses to external stimuli, which enables simultaneous measurement of multiple parameters. To enhance the sensing accuracy, a neural network model is used to demodulate the sensor responses. A proof-of-concept sensor using a UV-curable polymer as a waveguide material is demonstrated for simultaneous measurement of temperature and salinity of salt solutions. Although we only demonstrate the measurement of two parameters, the proposed sensor has the capability to measure more parameters if a multilayer waveguide structure made of different functional materials is used. The proposed sensor can benefit multifunctional analysis in a broad range of biological, chemical, and environmental monitoring applications.

Plasmonically Enhanced Colloidal Quantum Dot/Graphene Doped Polymer Random Lasers.

An improvement in random lasers based on a colloidal quantum dot (QD)/graphene-doped polymer was observed and attributed to multiple light-scattering and graphene surface plasmon resonance. The emission characteristics of quantum dots doped with graphene oxide and reduced graphene oxide were compared. The QD/reduced graphene oxide hybrid exhibited a lower laser emission threshold (~460 μJ/cm2). The emission modes and thresholds were strongly dependent on both the graphene doping concentration and the external temperature. Decreased plasmon coupling was the primary reason for lower QD/graphene laser emission with increasing temperature. The optimum reduced graphene oxide concentration was 0.2 wt.%. This work provides a practical approach to optimizing the threshold and stability of random laser devices, with potential applications in displays, sensors, and anti-counterfeiting labels.

Readily tunable surface plasmon resonances in gold nanoring arrays fabricated using lateral electrodeposition.

Generation and fine-tuning of surface plasmon resonances is a prerequstite for several established and emerging applications such as photovoltaics, photocatalysis, photothermal therapy, surface-enhanced spectroscopy, sensing, superlensing and lasing. We present a low-cost and scalable lateral electrodeposition method for fabrication of high aspect ratio gold nanoring arrays that exhibit multiple surface plasmon resonances in the visible to near-infrared region. Nickel disc arrays of 2 µm size were initially fabricated using maskless lithography and e-beam evaporation. Selective electrodeposition of gold on the lateral surfaces of nickel disc arrays was achieved using a 50 nm SiO2 film as an insulating mask. Growing from miniscule 100 nm wide lateral surfaces of nickel discs, nanorings with height up to 1084 nm could be obtained with their thickness and aspect ratio governed by the duration of electrodeposition. Facile tuning of the number of plasmon resonances, their resonant wavelength and relative intensity is demonstrated with applications in plasmon mediated photocatalysis and surface-enhanced Raman scattering.

A Wedge-Shaped Au Thin Film: Integrating Multiple Surface Plasmon Resonance Sensors in a Single Chip and Enhancing the Figure of Merit

We show here the design, fabrication, and characterization of a wedge-shaped Au thin film with an enhanced figure of merit (FOM). This is achieved by using a reflectivity change in an attenuated total reflection (ATR) setup by slightly modulating the wavenumber of the surface plasmon polariton by means of the varying thickness of the Au thin film. The wedge-shaped Au thin film is equivalent to multiple surface plasmon resonance (SPR) transducers integrated in a single chip and was fabricated by an electron-beam evaporation process with the position of the shutter controlled during the deposition. The FOM, defined as the difference between the maximum and minimum values of the normalized reflectivity change (ΔR/R) divided by the corresponding difference of the incident angles, was 8.0-times larger than that based on the reflectivity R. Also, we demonstrated that the wedge-shaped Au thin film was able to detect ethanol gas at a concentration of 0.2%, corresponding to a refractive index change of 2 × 10−5, without any surface functionalization. Since the sensing signal can be obtained with a single image from the wedge-shaped Au thin film without precise thickness control of the metal thickness, no other materials or modulation equipment is necessary, and the sensing chip can be employed in simple and highly sensitive systems.

Plasmonic sensor with self-reference capability based on functional layer film composed of Au/Si gratings

We propose a simple one-dimensional grating coupling system that can excite multiple surface plasmon resonances for refractive index (RI) sensing with self-reference characteristics in the near-infrared band. Using theoretical analysis and the finite-difference time-domain method, the plasmonic mechanism of the structure is discussed in detail. The results show that the excited resonances are independent of each other and have different fields of action. The mode involving extensive interaction with the analyte environment achieves a high sensitivity of 1236 nm/RIU, and the figure of merit (FOM) can reach 145 RIU−1. Importantly, the mode that is insensitive to the analyte environment exhibits good self-reference characteristics. Moreover, we discuss the case of exchanging the substrate material with the analyte environment. Promising simulation results show that this RIsensor can be widely deployed in unstable and complicated environments

A novel plasmonic refractive index sensor based on gold/silicon complementary grating structure* *Project supported by the National Natural Science Foundation of China (Grant No. 61865008) and the Scientific Research Fund of Sichuan Provincial Science

A novel complementary grating structure is proposed for plasmonic refractive index sensing due to its strong resonance at near-infrared wavelength. The reflection spectra and the electric field distributions are obtained via the finite-difference time-domain method. Numerical simulation results show that multiple surface plasmon resonance modes can be excited in this novel structure. Subsequently, one of the resonance modes shows appreciable potential in refractive index sensing due to its wide range of action with the environment of the analyte. After optimizing the grating geometric variables of the structure, the designed structure shows the stable sensing performance with a high refractive index sensitivity of 1642 nm per refractive index unit (nm/RIU) and the figure of merit of 409 RIU−1. The promising simulation results indicate that such a sensor has a broad application prospect in biochemistry.

Multi-plasmon resonances enhanced two-photon coherent anti-Stokes Raman scattering by nanorods.

The development of new structures allows two-photon coherent anti-Stokes Raman scattering (TPCARS) to be strongly enhanced by multiple surface plasmon resonances (MSPRs). In this paper, plasmonic structure consisting of two Ag nanorods is designed and the enhancement of TPCARS is investigated. By properly selecting designing structure parameters, strong MSPRs peaks at 1020nm and 505nm are obtained, which can enhance the TPCARS signal based on the frequency match of the fundamental frequency and frequency doubling. The enhancement factor of TPCARS can reach as high as 3.66×1028 with significant electric field enhancements under appropriate selection of system parameters. Furthermore, the two-photon process can be controlled at different optical frequencies by changing the geometric parameters of Ag nanorods. The new scheme advanced in this work can help to achieve single molecule level of CARS, and may have a potential to increase the intensity and resolution of nonlinear optical imaging.

Extension of the Measurable Wavelength Range for a Near-Infrared Spectrometer Using a Plasmonic Au Grating on a Si Substrate.

In this paper, we proposed near-infrared spectroscopy based on a Si photodetector equipped with a gold grating and extended the measurable wavelength range to cover 1200–1600 nm by improving a spectrum derivation procedure. In the spectrum derivation, photocurrent data during alteration of the incidence angle of the measured light were converted using a responsivity matrix R, which determines the spectroscopic characteristics of the photodetector device. A generalized inverse matrix of R was used to obtain the spectrum and to fit a situation where multiple surface plasmon resonance (SPR) peaks appeared in the scanning range. When light composed of two wavelengths, 1250 nm and 1450 nm, was irradiated, the two wavelengths were distinctively discriminated using the improved method.

Double Plasmon Resonance Nanostructured Silver Coatings with Tunable Properties

Plasmonic materials that exhibit dual or multiple localised surface plasmon resonances (LSPRs) due to their high application potential in biosensing and biodetection are gaining increasing attention. Here, we report on the novel strategy suitable for the production of silver nanostructured dual-LSPR coatings. This fully vacuum-based technique uses a magnetron sputtering of Ag and a gas aggregation source of silver nanoparticles. It is shown that when combined, produced Ag nano-islands and nanoparticles exhibit due to their different sizes and shapes two independent LSPRs in the visible part of spectra. Furthermore, the intensities and positions of individual LSPR may be precisely controlled by the amount of sputter-deposited nano-islands and a number of Ag nanoparticles, which opens new possibilities for the tailor-made production of novel platforms for surface-enhanced spectroscopic biodetection.

Multiple surface plasmon resonances enhanced nonlinear optical microscopy

Abstract The nonlinear optical microscopies of coherent two-photon excited fluorescence and anti-Stokes Raman scattering are strongly enhanced by multiple surface plasmon resonances (MSPRs). The Au@Ag nanorods presented strong MSPRs peaks at 800 and 400 nm, and can enhance nonlinear optical microscopy at fundamental and double frequencies, respectively. A two-dimensional (2D) material of g-C3N4 is employed to study the plasmon-enhanced nonlinear optical microscopy by the femtosecond laser. The electric analysis reveals that the MSPRs of the Au@Ag nanorod can significantly enhance the signals of two-photon excited fluorescence and anti-Stokes Raman scattering by up to the orders of 104 and 1016, respectively. The results demonstrate the great advantages of plasmon-enhanced nonlinear optical microscopy for the optical analysis on 2D materials, thus providing a new adventure for increasing the optical resolutions of nonlinear optical microscopy.

Enhanced organic solar cell performance: Multiple surface plasmon resonance and incorporation of silver nanodisks into a grating-structure electrode

In this study, plasmonic nanostructures were examined to enhance the light harvesting of organic thin-film solar cells (OSCs) by multiple surface plasmon resonance (SPR) phenomena originating from the grating-coupled configuration with a Blu-ray Disc recordable (BD-R)-imprinted aluminum (Al) grating structure and the incorporation of a series of silver nanodisks (Ag NDs). The devices with such a configuration maximize the light utilization inside OSCs via light absorption, light scattering, and trapping via multiple surface plasmon resonances. Different types and sizes of metallic nanoparticles (NPs), i.e., gold nanoparticles (Au NPs), Ag nanospheres (Ag NSs), and Ag NDs, were used, which were blended separately in a PEDOT:PSS hole transport layer (HTL). The device structure comprised of grating-imprinted-Al/P3HT:PCBM/Ag ND:PEDOT:PSS/ITO. Results obtained from the J–V curves revealed that the power conversion efficiency (PCE) of grating-structured Al/P3HT:PCBM/PEDOT:PSS/ITO is 3.16%; this value is ~6% higher than that of a flat substrate. On the other hand, devices with flat Al and incorporated Au NPs, Ag NSs, or Ag NDs in the HTL exhibited PCEs ranging from 3.15% to 3.37%. Furthermore, OSCs with an Al grating substrate were developed by the incorporation of the Ag ND series into the PEDOT:PSS layer. Compared with that of a reference device, the PCEs of the devices increased to 3.32%–3.59% (11%–20% improvement), indicating that the light absorption enhancement at the active layer corresponds to the grating-coupled surface plasmon resonance and localized surface plasmon resonance excitations with strong near-field distributions penetrating into the active layer leading to higher efficiencies and subsequent better current generation.

Transformative Heterointerface Evolution and Plasmonic Tuning of Anisotropic Trimetallic Nanoparticles.

Multicomponent nanoparticles that incorporate multiple nanocrystal domains into a single particle represent an important class of material with highly tailorable structures and properties. The controlled synthesis of multicomponent NPs with 3 or more components in the desired structure, particularly anisotropic structure, and property is, however, challenging. Here, we developed a polymer and galvanic replacement reaction-based transformative heterointerface evolution (THE) method to form and tune gold-copper-silver multimetallic anisotropic nanoparticles (MAPs) with well-defined configurations, including structural order, particle and junction geometry, giving rise to extraordinarily high tunability in the structural design, synthesis and optical property of trimetallic plasmonic nanoantenna structures. MAPs can easily, flexibly integrate multiple surface plasmon resonance (SPR) peaks and incorporate various plasmonic field localization and enhancement within one structure. Importantly, a heteronanojunction in these MAPs can be finely controlled and hence tune the SPR properties of these structures, widely covering UV, visible and near-infrared range. The development of the THE method and new findings in synthesis and property tuning of multicomponent nanostructures pave ways to the fabrication of highly tailored multicomponent nanohybrids and realization of their applications in optics, energy, catalysis and biotechnology.

Photoluminescence Enhancement of Silicon Quantum Dot Monolayer by Double Resonance Plasmonic Substrate

A structure composed of a monolayer of luminescent silicon quantum dots (Si-QDs) and a silver (Ag) film over nanosphere (AgFON) plasmonic nanostructure is prepared by precisely controlling the distance. A AgFON structure modifies both the photoluminescence (PL) and the PL excitation (PLE) spectra of a Si-QD monolayer significantly. It is shown that the spectral shape is very sensitive to the spacer thickness and the wavelength dependence of the PL and PLE enhancement factors agrees well with the absorptance spectra. Due to multiple surface plasmon resonances of a AgFON structure, in proper spacer thicknesses, simultaneous enhancements of the excitation cross section and the emission rate are achieved. In the wavelength range where the absorption cross section of Si-QDs is small, the PL enhancement factor averaged in a relatively wide region (10 × 10 mm2) reaches 12.

Morphology-Controlled Synthesis of Hybrid Nanocrystals via a Selenium-Mediated Strategy with Ligand Shielding Effect: The Case of Dual Plasmonic Au-Cu2-xSe.

Integrating a plasmonic metal and a semiconductor at the nanoscale is of great importance for exploring their optical coupling properties. However, the synthesis and fine structural control of such nanostructures remain challenging. Herein we report the facile aqueous-phase Se-mediated overgrowth of metal selenides onto Au nanocrystals. Taking plasmonic Cu2-xSe as an example, the introduction of a Se template allows deposition of large Cu2-xSe crystalline grains onto Au nanocrystal seeds in various shapes, including spheres, rods, and plates. Moreover, the configuration of Au-Cu2-xSe hybrids can be tuned from core-shell to heterodimer structure by controlling the growth behavior of the Se template. Se overgrowth depends critically on the absorption strength of stabilizers on Au seeds: a strongly absorbing stabilizer inhibits isotropic overgrowth, which is in agreement with molecular dynamics simulations. The resultant Au-Cu2-xSe hybrid nanocrystals possess multiple surface plasmon resonance modes. Finally, our synthetic strategy can be extended to prepare other Au-metal selenide hybrids such as Au-Ag2Se and Au-CdSe with controllable morphologies.

Multiple surface plasmon resonances of square lattice nanohole arrays in Au-SiO2-Au multilayer films

The optical properties and the local electromagnetic field enhancement of a multilayer structure with square lattice nanohole arrays in Au-SiO2-Au multilayer films are numerically studied using finite-difference time domain method. Simulation results demonstrate that the multiple surface plasmons (SP) resonances consist of SP on the air/Au interface, SiO2/Au interfaces (the middle layers), Au/SiO2 interface (the lower layer) and coupling modes on the Au film and Au film. We investigated some of structure parameters that influence the SP resonances of the multilayer nanostructure. Adjustment of the thickness of SiO2 film (H2), the diameter (R) of circular nanoholes, the periods (C) of square lattice and the thickness of Au film (H1) could change the absorption intensity and the SP resonances. The simulation of the electromagnetic field distributions shows that the location of the local electromagnetic field enhancement can specify the different SP resonances patterns. Dipole, quadrupole, and twelve-pole SP resonances modes can be found in the multilayer nanostructure. These studies are important for applications using multiple SP resonances.

Topography effects in AFM force mapping experiments on xylan-decorated cellulose thin films

Abstract Xylan-coated cellulose thin films has been investigated by means of atomic force microscopy (AFM) and force mapping experiments. The birch xylan deposition on the film was performed under control by means of a multiple parameter surface plasmon resonance spectroscopy (MP-SPR) under dynamic conditions. The coated films were submitted to AFM in phase imaging mode to force mapping with modified AFM tips (sensitive to hydrophilic OH and hydrophobic CH3 groups) in order to characterize and localize the xylan on the surfaces. At the first glance, a clear difference in the adhesion force between xylan-coated areas and cellulose has been observed. However, these different adhesion forces originate from topography effects, which prevent an unambiguous identification and subsequent localization of the xylan on the cellulosic surfaces.