Sensitivity Enhanced by MoS2–Graphene Hybrid Structure in Guided-Wave Surface Plasmon Resonance Biosensor

Plasmonics - Compared with surface plasmon resonance (SPR) biosensor, guided-wave surface plasmon resonance (GWSPR) biosensor has a higher sensitivity. In order to further enhance the sensitivity...     

Localized Surface Plasmon Resonance and Refractive Index Sensitivity of Metal–Dielectric–Metal Multilayered Nanostructures

The localized surface plasmon resonances of multilayered nanostructures are studied using finite difference time domain simulations and plasmon hybridization method. Concentric metal–dielectric–metal (MDM) structure with metal core and nanoshell separated by a thin dielectric layer exhibits a strong coupling between the core and nanoshell plasmon resonance modes. The coupled resonance mode wavelengths show dependence on the dielectric layer thickness and composition of core and outer layer metal. The aluminum-based MDM structures show lower plasmon wavelength compared with Ag- and Au-based MDM nanostructures. The calculated refractive index sensitivity (RIS) factor is in the order Ag–Air–Ag>Au–Air–Au>Al–Air–Al for monometallic multilayered nanostructures. Bimetallic multilayered nanostructures support strong and tunable plasmon resonance wavelengths as well as high RIS factor of 510 nm/refractive index unit (RIU) and 470 nm/RIU for Al–Air–Au and Ag-Air-Au, respectively. The MDM structures not only exhibit higher index sensitivity but also cover a wide ultraviolet–near-infrared wavelengths, making these structures very promising for index sensing, biomolecule sensing, and surface-enhanced Raman spectroscopy.     

Optical Magnetism in Surface Plasmon Resonance–Based Sensors for Enhanced Performance

Surface plasmon resonance (SPR)–based structures are finding important applications in sensing biological as well as inorganic samples. In SPR techniques, an angle-resolved reflection (R) profile of the incident light from a metal-dielectric interface is measured and the resonance characteristics are extracted for the identification of the target sample. However, the performance, and hence the applicability of these structures, suffers when the weight and concentration of the target samples are small. Here, we show that SPR-based sensors can create strong magnetism at optical frequency, which can be used for the detection of target samples instead of using the conventional R profiles, as the magnetic resonance varies depending on the refractive index of the target sample. Using scattering parameters retrieval method, we computationally find out the effective permeability (μ_eff) of a SPR sensor with a structure based on Kretschmann configuration, and use it to calculate the performance of the sensor. A comparison with the conventional technique that uses R profile to detect a target sample shows a significant increase in the sensor performance when μ_eff is used instead.

     

Long-Range Surface Plasmon Resonance–Based Sensitivity Study on D-shaped Ag-MgF2-Coated Models with Analyte Variations

In this report, a novel D-shaped long-range surface plasmon resonance (LRSPR) fiber base sensor has been introduced. The demonstration of proposed sensor involves two D-shaped silver-coated models to study the sensitivity responses. The entire study with the constructed models is based on a single-mode fiber. The models are multilayered consisting of metal, dielectric, and analyte as separate layers. Silver (Ag) and magnesium fluoride (MgF2) strips are used as metal and dielectric layers respectively. The constituency of analyte as an interface excellently standardized the models for sensitivity detection. In this report, a large range of analyte refractive indices (RI) which varies from 1.33 to 1.38 is appraised for the proposed models to characterize the sensitivity. The entire context is encompassed by the wavelength region from 450 to 850 nm with an interval of 20 nm. Sensitivities in this report are measured based on the analyte position from the core and metal for both models. For each of the two models, the analyte is placed as the top layer. RIs of the applied metal (Ag) are measured using the Drude-Lorentz formula. The simulated sensitivities for model-1 and model-2 vary from 6.3?×?10³ nm/RIU to 8.7?×?10³ nm/RIU.

     

Optical Biochip with Multichannels for Detecting Biotin–Streptavidin Based on Localized Surface Plasmon Resonance

A rapid and accurate detection of molecular binding of antigen-antibody signaling in high throughput is of great importance for biosensing technology. We proposed a novel optical biochip with multichannels for the purpose of detection of biotin–streptavidin on the basis of localized surface plasmon resonance. The optical biochip was fabricated using photolithography to form the microarrays functioning with multichannels on glass substrate. There are different nanostructures in each microarray. Dry etching and nanosphere lithography techniques were applied to fabricate Ag nanostructures such as hemispheres, nanocylindricals, triangular, and rhombic nanostructures. We demonstrated that 100-nM target molecule (streptavidin) on these optical biochips can be easily detected by a UV-visible spectrometer. It indicated that period and shape of the nanostructures significantly affect the optical performance of the nanostructures with different shapes and geometrical parameters. Our experimental results demonstrated that the optical biochips with the multichannels can detect the target molecule using the microarrays structured with different shapes and periods simultaneously. Batch processing of immunoassay for different biomolecular through the different channels embedded on the same chip can be realized accordingly.     

BaTiO3-Graphene-Affinity Layer–Based Surface Plasmon Resonance (SPR) Biosensor for Pseudomonas Bacterial Detection

Plasmonics - In the present work, a highly sensitive SPR biosensor based on silver (Ag), barium titanate (BaTiO3), graphene, and affinity layer is proposed for the detection of Pseudomonas...     

Highly Sensitive Nitrogen Dioxide Sensor Based on Enhancement of Surface Plasmon Resonance Response in Glass Waveguides by C–Ag Nanodots

Continuous monitoring of air quality and rapid detection of pollutants are highly desirable in urban planning and development of smart cities. One of the primary greenhouse gases responsible for environmental degradation and respiratory diseases is nitrogen dioxide (NO₂). Existing gas sensors for measuring NO₂ concentration suffer from drawbacks such as cross-sensitivity, limited range, and short life span. On the other hand, optical sensors, in particular, surface plasmon resonance (SPR) sensors, have emerged as a preferred alternative owing to advantages like high selectivity, immunity to electromagnetic interference, and low response time. In this work, we design and simulate a NO₂ sensor based on a glass waveguide coated with a gold film. Surface plasmons are excited at the interface by a 400–500-nm light source, incident at an angle of 43.16°. To enhance the sensitivity, we further coat the waveguide with three layers of carbon-silver (C–Ag) nanodots, which increases the surface plasmon field amplitude by nearly 7 times, in the absence of NO₂. When NO₂ concentration is varied in the range of 0–200 ppm, a corresponding change is observed in the reflected amplitude. In the absence of the C–Ag nanodots layer, the sensitivity is only 0.00042%/ppm, and on addition of C–Ag nanodots, the sensitivity increases significantly to 0.14235%/ppm which is nearly 343 times higher. These results demonstrate the efficiency of implementing nanodots in SPR sensor to detect and trace concentrations of contaminants in the gas phase.

     

Surface Plasmon Resonance and Absorption Features Beyond the Bandedge in ZnO Nanorods Array – Au Heterostructures: Prediction and More Accurate Representation

Plasmonics - Well-oriented zinc oxide nanorods arrays (ZnO NRsA) have been grown on seeded substrates. The morphology, chemical, and vibrational characteristics of the nanostructures were...     

Ultrahigh Sensitivity Surface Plasmon Resonance–Based Fiber-Optic Sensors Using Metal-Graphene Layers with Ti3C2Tx MXene Overlayers

Plasmonics - Precise detection of volatile organic compounds (VOCs) using high-sensitivity fiber-optic probes is highly desirable for rapid screening in the fields of medicine and food processing....     

Surface Plasmon Resonance on the Antimonene–Fe2O3–Copper Layer for Optical Attenuated Total Reflection Spectroscopic Application

In this paper, we explore a highly sensitive surface plasmon resonance (SPR) structure. The configuration fabricated by the antimonene-Fe₂O₃-copper (Cu) is theoretically analyzed. Fe₂O₃ work as dielectric nanosheets to enhance the sensitivity. Besides, the x components of the electric field also can be improved. As promising two-dimensional (2D) material with a stronger interaction with biomolecules and higher chemical stability, antimonene exhibits potential applications in sensing. By optimizing the configuration parameters, the highest angular sensitivity of 398°/RIU. The result displays that the sensitivity is enhanced by 79.3% compared with the conventional configuration with a single Cu film. We hope that the simple configuration will find the suitable application value.

     

Optimization of the Field Enhancement and Spectral Bandwidth of Single and Coupled Bimetal Core–Shell Nanoparticles for Few-Cycle Laser Applications

We have theoretically studied and optimized the field enhancement and temporal response of single and coupled bimetal Ag/Au core–shell nanoparticles (NPs) with a diameter of 160 nm and compared the results to pure Ag and Au NPs. Very high-field enhancements with an amplitude reaching 100 (with respect to the laser field centered at 800 nm) are found at the center of a 2-nm gap between Ag/Au core–shell dimers. We have explored the excitation of the bimetal core–shell particles by Fourier transform-limited few-cycle optical pulses and identified conditions for an ultrafast plasmonic decay on the order of the excitation pulse duration. The high-field enhancement and ultrafast decay makes bimetal core–shell particles interesting candidates for applications such as the generation of ultrashort extreme ultraviolet radiation pulses via nanoplasmonic field enhancement. Moreover, in first experimental studies, we synthesized small bimetal Ag/Au core–shell NPs and compared their optical response with pure Au and Ag NPs and numerical results.     

Elucidating the Signal Responses of Multi-Parametric Surface Plasmon Resonance Living Cell Sensing: A Comparison between Optical Modeling and Drug–MDCKII Cell Interaction Measurements

In vitro cell-based assays are widely used during the drug discovery and development process to test the biological activity of new drugs. Most of the commonly used cell-based assays, however, lack the ability to measure in real-time or under dynamic conditions (e.g. constant flow). In this study a multi-parameter surface plasmon resonance approach in combination with living cell sensing has been utilized for monitoring drug-cell interactions in real-time, under constant flow and without labels. The multi-parameter surface plasmon resonance approach, i.e. surface plasmon resonance angle versus intensity plots, provided fully specific signal patterns for various cell behaviors when stimulating cells with drugs that use para- and transcellular absorption routes. Simulated full surface plasmon resonance angular spectra of cell monolayers were compared with actual surface plasmon resonance measurements performed with MDCKII cell monolayers in order to better understand the origin of the surface plasmon resonance signal responses during drug stimulation of cells. The comparison of the simulated and measured surface plasmon resonance responses allowed to better understand and provide plausible explanations for the type of cellular changes, e.g. morphological or mass redistribution in cells, that were induced in the MDCKII cell monolayers during drug stimulation, and consequently to differentiate between the type and modes of drug actions. The multi-parameter surface plasmon resonance approach presented in this study lays the foundation for developing new types of cell-based tools for life science research, which should contribute to an improved mechanistic understanding of the type and contribution of different drug transport routes on drug absorption.     

Buried Effects of Surface Plasmon Resonance Modes for Periodic Metal–Dielectric Nanostructures Consisting of Coupled Spherical Metal Nanoparticles with Cylindrical Pore Filled with a Dielectric

We numerically investigate the buried effects of surface plasmon resonance (SPR) modes for the periodic silver-shell nanopearl dimer (PSSND) array and their solid counterparts with different buried depths in a silica substrate by means of finite element method with three-dimensional calculations. The investigated PSSND array is an important novel geometry for plasmonic metal nanoparticles (MNPs), combining the highly attractive nanoscale optical properties of both metallic nanoshell and cylindrical pore filled with a dielectric. Numerical results for SPR modes corresponding to the effects of different illumination wavelengths, absorption spectra, pore–dielectric, electric field components and total field distribution, charge density distribution, and the model of the induced local field or an applied field of the PSSND array are reported as well. It can be found that the buried MNPs with cylindrical pore filled with a dielectric in a substrate exhibit tunable SPR modes corresponding to the bonding and antibonding modes that are not observed for their solid counterparts.     

Use of Surface Plasmon Resonance and Biolayer Interferometry for the Study of Protein–Protein Interactions on the Example of an Enzyme of a Glycosyl Hydrolase Subtype (EC 3.2.1) and Specific Antibodies to It

Two previously obtained, full-size, fully human antibodies that reversibly bind the active form of an enzyme belonging to the subtype EC 3.2.1, which is used for substitutive enzymatic therapy in lysosomal storage diseases, have been characterized by surface plasmon resonance and biolayer interferometry methods. It was shown under normal physiological conditions that the designed antibodies specifically bound with the antigen (KD ~ 10^–8 M) and rapidly dissociated at neutral pH in 60% ethylene glycol while leaving the enzymatic activity unchanged. Dan ue to their properties, the developed antibodies can be used in industry as affinity ligand in the isolation of therapeutic substances of the enzyme.     

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...