Influence of Dielectric Coating on Performance of Surface Plasmon Resonance Sensor

Plasmonics - In the present study, the nature of dielectric layer above metal layer in surface plasmon resonance sensor is investigated. The performance-defining parameters, i.e., shift in...     

Influence of an Electron Beam Exposure on the Surface Plasmon Resonance of Gold Nanoparticles

Electron beam imaging is a common technique used for characterizing the morphology of plasmonic nanostructures. During the imaging process, the electron beam interacts with traces of organic material in the chamber and produces a well-know layer of amorphous carbon over the specimen under investigation. In this paper, we investigate the effect of this carbon adsorbate on the spectral position of the surface plasmon in individual gold nanoparticles as a function of electron exposure dose. We find an optimum dose for which the plasmonic response of the nanoparticle is not affected by the imaging process.     

Nanostructuring of Continuous Gold Film by Laser Radiation Under Surface Plasmon Polariton Resonance Conditions

The physical mechanisms of metallic nanoparticles formation by laser technology were studied. The system air/Au film/glass was irradiated by laser at the conditions of surface plasmon resonance. A surface electromagnetic wave was excited in Kretchmann configuration by the fundamental and second harmonics of the Q-switched YAG/Nd⁺³ laser with pulse power density close to the threshold of melting. Nanostructuring of Au film was observed only for the second harmonic (λ = 0.532 μm) irradiation at the surface plasmon polariton resonance (SPR) conditions. Estimations were done using the interference model of the differently directed plasmon polariton waves excited by a surface electromagnetic wave on the metal surface. It was shown that a regular pattern of locally heated spots can be formed in a metallic film by pulsed laser irradiation. The spatial distribution of this pattern is close to the period of interference. The observed effect of laser nanofragmentation is explained by the self-organization of plasmon polariton subsystem in the process of Au nanoparticles formation at high laser intensity levels. These methods open new possibilities for nanostructured surfaces formation utilizing simple self-organization processes.     

Highly Sensitive Dual-core Photonic Crystal Fiber Based on a Surface Plasmon Resonance Sensor with Gold Film

Plasmonics - A highly sensitive surface plasmon resonance (SPR) sensor comprising a dual-core photonic crystal fiber (PCF) is designed to detect minute changes in analyte refractive indices (RIs)...     

Surface Plasmon Coupling Effect of Gold Nanoparticles with Different Shape and Size on Conventional Surface Plasmon Resonance Signal

The labeling strategy with gold nanoparticles for the conventional surface plasmon resonance (SPR) signal enhancement has been frequently used for the sensitive determination of small molecules binding to its interaction partners. However, the influence of gold nanoparticles with different size and shape on SPR signal is not known. In this paper, three kinds of gold nanoparticles, namely nanorods, nanospheres, and nanooctahedrons with different size, were prepared and used to investigate their effects on the conventional SPR signal at a fixed excitation wavelength 670 nm. It was found that the SPR signal (i.e., resonant angle shift) was varied with the shapes and sizes of gold nanoparticles in suspension at a fixed concentration due to their different plasmon absorbance bands. For gold nanorods with different longitudinal absorbance bands, three conventional SPR signal regions could be clearly observed when the gold nanorod suspensions were separately introduced onto the SPR sensor chip surface. One region was the longitudinal absorbance bands coinciding with or close to the SPR excitation wavelength that suppressed the SPR angle shift. The second region was the longitudinal absorbance bands at 624 to 639 and 728 to 763 nm that produced a moderate increase on the SPR resonant angle shift. The third region was found for the longitudinal absorbance bands from 700 to 726 nm that resulted in a remarkable increase in the SPR angle shift responses. This phenomenon can be explained on the basis of calculation of the correlation of SPR angle shift response with the gold nanorod longitudinal absorbance bands. For nanospheres and nanooctahedrons, the SPR angle shift responses were found to be particle shape and size dependent in a simple way with a sustaining increase when the sizes of the nanoparticles were increased. Consequently, a guideline for choosing gold nanoparticles as tags is suggested for the SPR determination of small molecules with binding to the immobilized interaction partners.     

Transmission Surface Plasmon Resonance Signal Enhancement via Growth of Gold Nanoparticles on a Gold Grating Surface

We developed a novel technique for increasing the sensitivity of transmission surface plasmon resonance (T-SPR) signals. T-SPR spectroscopy was performed by irradiating, with white light, a gold grating substrate whose surface was nanostructured by growing gold nanoparticles (AuNPs). AuNPs were grown directly on the substrate surface by alcohol reduction and their growth was observed at various stages by UV–visible spectroscopy and standard Kretschmann-type SPR spectroscopy. For comparison, normal gold film with smooth surface was examined under similar condition. The T-SPR results show a possibility of hybrid excitation of both localized and propagating surface plasmon. Significantly, T-SPR spectra of the gold grating substrate obtained during AuNP growth show stronger and narrower peaks in the range 650–800 nm. The maximum T-SPR excitation was at an incident angle of 35°. A layer-by-layer system of 5,10,15,20-tetrakis (1-methyl-4-pyridinio)porphyrin tetra(p-toluenesulfonate) molecules and sodium copper chlorophyllin molecules was used to verify the enhancement of the developed system. We believe that the AuNPs/Au grating for T-SPR devices will provide enhanced signals for detecting nanometer order materials and for high-sensitive sensor applications.     

Propagation Loss of Long-Range Surface Plasmon Polariton Gold Stripe Waveguides in the Thin-Film Limit

Propagation loss experienced by long-range plasmon polaritons in ultrathin gold stripe waveguides embedded in different polymer cladding materials was studied and correlated with atomic-scale characterization of the gold film structure. We identify the main sources of experimentally observed propagation loss which deviates from ideal values in the thin-film limit. Increased loss can be translated to an increased effective thickness of the ultrathin films due to incomplete surface coverage and the presence of diffuse interfaces, both of which depend significantly on the choice of cladding material. The results illustrate the importance of atomic-scale dynamics of metal film formation for the selection of optimum substrate materials for surface plasmon polariton waveguides, resonant transmission structures, and semitransparent electrical contacts.     

Localized Surface Plasmon Resonance in Gold Nanocluster Arrays on Opaque Substrates

Plasmonics - We report on the investigation of the localized surface plasmon resonance (LSPR) in periodical Au nanostructures. The arrays of Au nanoclusters and dimers were fabricated on Si and...     

Sensitivity Enhancement for Surface Plasmon Resonance Imaging Biosensor by Utilizing Gold�CSilver Bimetallic Film Configuration

Gold–silver bimetallic film configuration is brought forward to realize surface plasmon resonance imaging (SPRI) biosensor with the virtues of both high sensitivity and chemical stability. The theoretical calculation is adopted to optimize the thicknesses of the metal films, and bimetallic film configuration with high refractive index sensitivity and a good linearity between reflectivity and refractive index is presented. Then, the property of the detection system is discussed. The results show that in comparison to most commercial SPRI biosensors which use single gold films, the sensitivity and molecule detection ability of the gold–silver bimetallic film configuration can be improved to a great extent. For the substrate of BAK3 glass used in this paper, the sensitivity enhancement reaches as high as 80%, which makes it a much better choice for SPRI biosensing applications.     

Influence of Cr Adhesion Layer on Detection of Amyloid-Derived Diffusible Ligands Based on Localized Surface Plasmon Resonance

A Cr adhesion layer inserted between Ag nanoparticles and a glass substrate, for the purpose of improving the adhesion of Ag nanoparticles to glass, was observed to cause an abnormal peak shift of extinction spectra in non-specific reactions. The undesired peak shift misleads molecule detection in non-specific reactions. To solve this issue, a practical technique using n-propyl-trimethoxysilane-based passivation for the detection of amyloid-derived diffusible ligands was investigated as a route to eliminate the abnormal peak shifting observed in the non-specific reactions. To evaluate this passivation technique, localized surface plasmon resonance immunoassay experiments were conducted. Experimental results derived with and without the passivation process were investigated as a basis for comparative analysis. Our experimental results demonstrate that this passivation technique effectively eliminates the observed peak shift originating from the Cr adhesion layer.     

Distance-Dependent Surface Plasmon Resonance Coupling Between a Gold Grating Surface and Silver Nanoparticles

Plasmonics - In this study, we achieved an enhancement of the transmission surface plasmon resonance (T-SPR) intensity by depositing silver nanoparticles (AgNPs) onto a gold grating substrate. The...     

Co-existence of Radiative and Non-Radiative Surface Plasmon Resonance Modes: Power Balance and Influence of Film Morphology

Plasmonics - The power balance and conditions of co-existing radiative and non-radiative surface plasmon resonance modes have been exploited at the metal film-water interface. Angular (AIM) and...     

Light Humidity Sensor of Surface Plasmon Resonance by Symmetric Metal Film

The field of plasmonics has experienced a renaissance in recent years by providing a large variety of new physical effects and applications. Here, we demonstrate a light humidity sensor of surface plasmon resonance (SPR) by a symmetric metal film, which uses P polarised light of emergent He–Ne laser to stimulate SPR. Resonance angle change received by the spectrum detector can determine humidity via the relationship between humidity and effective refractive index. When the relatively short wavelengths are shown in the model, the evanescent wave penetration depth is shallow, resonance state is weak and energy loss is low. The opposite results are obtained, when the wavelength is long. Also, with increasing thickness, the resonance peak becomes acute, thereby indicating the improvement in detection accuracy. When the metal thickness of our model is 50 nm, the resonance peak of the reflection spectrum is narrower, accuracy is high and reflectivity is close to 0. By analysing the experimental results, the SPR resonance phenomenon is shown. The electromagnetic field energy is highly concentrated near the interface between the metal and SiO₂, which appears highly localized. The resolution of the structure can reach 0.37% RH (relative humidity), which is significantly more than the resolution of capacitive humidity sensor, i.e., resolution is usually 1% RH to 2% RH. The optical sensor of our development can provide a key device for long-distance transmission sensing, in special conditions such as low temperature.

     

Slab Thickness Dependence of Localized Surface Plasmon Resonance Behavior in Gold Nanorings

We present detailed experimental and numerical studies of plasmonic properties of gold nanoring (NR) arrays with different slab thicknesses from 15 to 125 nm. The hybrid plasmon resonances for the bonding and antibonding modes in gold NRs exhibit a high slab thickness dependence behavior in optical properties. For the thinner slab thickness below 50 nm, both hybrid modes show large spectral tunabilities by varying the slab thickness. Furthermore, for such hollow NR structure, the enhancements of electric field intensities at the inner and outer ring surfaces when reducing the slab thickness are investigated. We observe a significant transition of field distributions for the antibonding mode. All these features can be understood by surface charge distributions from our simulations. The results of this study offer a potential strategy to design a composite plasmonic nanostructure with large field enhancement for numerous applications.     

Surface Plasmon Resonance Intensification by Cavity-Ring Plasma Structure in the Giga-Hertz Regime

In this paper, we propose a novel sub-wavelength plasma structure that can effectively enhance surface plasmon resonance (SPR) to achieve a significant local field. On the basis of a plasma ring structure, we add a slit and two thin plasma layers, working as a metal-insulator-metal (MIM) waveguide at a specific incident wave frequency and generate the Fabry-Perot resonance (FPR). The structure thus couples the incident wave energy to the vicinity of the slit and intensifies the SPR inside the plasma ring. In addition, we also find the coupling and competing between SPR and FPR. For the coupling mode, the average field enhancement in the ring is up to a factor of 9.7. Moreover, the optimized thickness of the plasma layer is much thinner than the skin depth of the plasma to ensure the incident wave easily entering the MIM waveguide. We further calculate the dispersion relationship of surface plasmon polaritons in the waveguide cavity. The simulation results and theoretical dispersion function are in good agreements.

     

Surface Plasmon Resonance in Small Gold Nanoparticles: Introducing a Size-Dependent Plasma Frequency for Nanoparticles in Quantum Regime

Plasmonics - Study of surface plasmon resonance for small nanoparticles (R < 10 nm) has many theoretical complexities due to lack of a simple quantitative model for describing...     

Near-Infrared Dye Immobilized in Porous Silica Layer on Gold Nanorod and Its Fluorescence Enhancement by Strengthened Electromagnetic Field Based on Surface Plasmon Resonance

We report immobilizing Nile Blue A, which is a cationic fluorescent dye emitting in the near-infrared region, in the porous silica layer on gold nanorod and its fluorescence enhancement by strengthened electromagnetic field based on surface plasmon resonance. The effect of the spacer corresponding to the silica layer on the metal-enhanced fluorescence effect is also discussed in detail. Hollow silica nanorod was in advance prepared, and then the silica layer was partly etched to increase the porosity for the improvement of the mass transfer. Subsequently, gold nanorod was fabricated in the restricted space of hollow silica nanorod. Finally, Nile Blue A was physically immobilized in the porous silica layer on gold nanorod through electrostatic interactions. The fluorescence enhancement of Nile Blue A based on surface plasmon resonance was semi-quantified by comparative experiments using hollow silica nanorod, which is exactly the same structure except for gold as silica-coated gold nanorod. Since our results demonstrated that the porosity degree of the silica layer significantly affected the fluorescence enhancement of Nile Blue A, it is hopeful that our design concept, distinct from the conventional one, can lay a foundation for further development of near-infrared fluorescence nanomaterials.