Induced Surface Plasmon Resonance Research Articles

Reflex optical fiber probe for simultaneous determination of seawater salinity and temperature by surface plasmon resonance

A new high-sensitivity optical reflective probe is reported for the simultaneous measurement of seawater salinity and temperature. A concise interference structure was used for exciting the cladding mode. A nanoscale gold film served as the sensitive detection area to induce surface plasmon resonance (SPR). A photosensitive material (polydimethylsiloxane) was partially coated on the sensitive layer to produce double SPR peaks. The SPR effect model of the optical fiber structure was modified and a complete detection system was constructed. The preparation and structural parameters were optimized to obtain high-quality spectral properties. Through the calibration experiments, the response to salinity at its characteristic wavelength had a sensitivity of 0.0558 nm/%, while the temperature response at its characteristic wavelength was −4.418 nm/°C. The reflective probe was shown to have low crossover sensitivity. Compared with standard instrumentation, this device was shown to be stable and precise and is expected to have significant practical applications.

Signal Enhancement Strategies for Refractive Index-Sensitive Nanobiosensor.

Direct bio-monitoring essentially involves optical means since photon has insignificant effects over biomolecules. Over the years, laser induced surface Plasmon resonance method with various modifications as well as versatile localized Plasmon excited by incoherent light have facilitated in recording many nanobiological activities. Yet, monitoring interactions of small molecules including drugs requires signal amplification and improvement on signal-to-noise ratio. This paper focused on how the refractive index based nanobio-sensoring gold platform can produce more efficient, adaptable and more practical detection techniques to observe molecular interactions at high degree of sensitivity. It discusses surface chemistry approach, optimisation of the refractive index of gold platform and manipulation of gold geometry augmenting signal quality. In a normal-incidence reflectivity, r0 can be calculated using the Fresnel equation. Particularly at λ = 470 nm the ratio of r / r0 showed significant amplitude reduction mainly stemmed from the imaginary part of the Au refractive index. Hence, the fraction of reduction, Δr = 1 - r / r0. Experimentally, in a common reference frame reflectivity of a bare gold surface, R0 is compared with the reflectivity of gold surface in the presence of biolayer, R. The reduction rate (%) of reflectivity, ΔR = 1 - R / R0 is denoted as the AR signal. The method therefore enables quantitative measurement of the surface-bound protein by converting ΔR to the thickness, d, and subsequently the protein mass. We discussed four strategies to improve the AR signal by changing the effective refractive index of the biosensing platform. They are; a) Thickness optimisation of Au thin layer, b) Au / Ag bimetallic layer, c) composing alloy or Au composite, and d) Au thinlayer with nano or micro holes. As the result we successfully 'move' the refractive index, ε of the AR platform (gold only) to ε = -0.948 + 3.455i, a higher sensitivity platform. This was done by composing Au-Ag2O composite with ratio = 1:1. The results were compared to the potential sensitivity improvement of the AR substrate using other that could be done by further tailoring the ε advanced method. We suggested four strategies in order to realize this purpose. It is apparent that sensitivity has been improved through Au/Ag bimetallic layer or Au-Ag2O composite thin layer, This study is an important step towards fabrication of sensitive surface for detection of biomolecular interactions.

One-step hydrothermal synthesis of peony-like Ag/Bi2WO6 as efficient visible light-driven photocatalyst toward organic pollutants degradation

Here, we report a simple approach to fabricate 3D hierarchical peony-like Ag/Bi2WO6 hybrid photocatalyst through one-step hydrothermal method with l-leucine as a template. The morphology and structure of the resultant materials were characterized by various analytical methods, such as X-ray diffraction, field emission scanning electron microscopy and UV–Vis diffuse reflectance spectra. The photocatalytic performance of Bi2WO6 and Ag/Bi2WO6 samples was evaluated by degrading organic dye and antibiotic in water under visible light irradiation. A series of results indicated that loaded Ag nanoparticles significantly improve the photocatalytic activity of Bi2WO6. In addition, the possible mechanism was proposed that the enhanced photocatalytic activity was resulted from the unique configuration of peony-like morphology that favorable for the adsorption of organic compounds and the high Schottky barriers between interface of Ag NPs and Bi2WO6, which promoted the transfer of photogenerated electrons from Bi2WO6 to Ag NPs. Meanwhile, noble metal Ag can induce surface plasmon resonance leading to the better visible light absorption of Bi2WO6.

Cancer cell death pathways caused by photothermal and photodynamic effects through gold nanoring induced surface plasmon resonance

The different death pathways of cancer cells under the conditions of the photothermal (PT), effect, photodynamic (PD) effect, and their combination are evaluated. By incubating cells with Au nanoring (NRI) either linked with the photosensitizer, AlPcS, or not, the illumination of a visible continuous laser for exciting the photosensitizer or an infrared femtosecond laser for exciting the localized surface plasmon resonance of Au NRI, leads to various PT and PD conditions for study. Three different staining dyes are used for identifying the cell areas of different damage conditions at different temporal points of observation. The cell death pathways and apoptotic evolution speeds under different cell treatment conditions are evaluated based on the calibration of the threshold laser fluences for causing early-apoptosis (EA) and necrosis (NE) or late-apoptosis (LA). It is found that with the PT effect only, strong cell NE is generated and the transition from EA into LA is faster than that caused by the PD effect when the EA stage is reached within 0.5 h after laser illumination. By combining the PT and PD effects, in the first few hours, the transition speed becomes lower, compared to the case of the PT effect only, when both Au NRIs internalized into cells and adsorbed on cell membrane exist. When the Au NRIs on cell membrane is removed, in the first few hours, the transition speed becomes higher, compared to the case of the PD effect only.

Characterization of advanced polymethylmethacrylate (PMMA) targets for TNSA laser irradiation

Characterization of advanced micrometric foils suitable for TNSA regime were performed using optical spectroscopy, microscopy and Nd:YAG low laser intensity. Micrometric acrylic beads were produced in polymethylmethacrylate foils through complex physical and technical procedures in order to enhance the absorption coefficient in the IR region. Moreover, Au nanoparticles were embedded in the polymer in order to induce surface plasmon resonance absorption and plasma electron density enhancement. The suitably prepared polymers were investigated at low laser intensity to have evidence of their capability to absorb IR wavelength radiations and promote enhancement of the plasma temperature and density. Results indicate that the high transparence of PMMA foils can be strongly reduced by the presences of the micrometric acrylic beads and that the obtainable laser-generated plasma improves the ion acceleration when high beads density and high Au nanoparticles concentrations are employed.

Using the Surface Plasmon Resonance of Au Nanoparticles to Enhance Ultraviolet Response of ZnO Nanorods-Based Schottky-Barrier Photodetectors

Surface plasmon resonance mediated by Gold (Au) nanoparticles (NPs) was employed to enhance the ultraviolet (UV) response of ZnO nanorod (NR)-based Schottky-barrier photodetectors (SB-PDs). The defect-level emissions of ZnO NRs induce surface plasmon resonance in Au NPs and enhance the electromagnetic field near Au NPs, which excites a great deal of electrons from Au NPs crossing over the barrier height of Au NP/ZnO interface. This causes the band-to-band emission of ZnO (384 nm) is increased by a magnitude of three, and the deep-level emissions (450-700 nm) are drastically decreased as compared to ZnO NRs without coverings of Au NPs. Also, it drastically enhances the UV (340 nm)-to-visible (560 nm) rejection ratio from 115 to 443. The effect of surface plasmon resonance is verified by that the responsivity of SB-PD with the covering of Au NPs exhibits a greater increasing with applied reverse-bias voltage than that without Au NPs.

Surface plasmon resonance enhanced highly efficient planar silicon solar cell

Metal nanoparticles (NPs) induced surface plasmon resonance (SPR) is of great interest for efficient controlling over light׳s propagation and absorption in optoelectronic devices applications. In this work, we proposed a simple strategy to improve the photocurrent of planar silicon (Si) p–n junction solar cells by attaching plasmonic Au nanoparticles (AuNPs) onto transparent graphene film to enhance incident light harvesting. Finite Element Method based simulations reveal that the strong light scattering by AuNPs is responsible for the optical absorption enhancement within Si, leading to the increase in photocurrent. In addition, decoration of AuNPs on graphene also contributes to a high fill factor (FF) by reducing series resistance in the circuit. These contributory factors, together with the effective surface passivation of Si yield a power conversion efficiency (PCE) as high as 10.15%, with excellent reproducibility. This study will open up new opportunities for the optimization of Si based optoelectronic devices.

Au-Mediated Surface Plasmon Enhanced Ultraviolet Response of p-Si/n-ZnO Nanorods Photodetectors

Surface plasmon resonance mediated by Gold (Au) nanoparticles (NPs) was employed to enhance the ultraviolet (UV) response of p-Si/n-ZnO nanorod (NR) heterojunction photodetectors (HPDs). In the ZnO NRs with Au NP covering, the photoluminescence spectrum shows that the band-to-band emission of ZnO (384 nm) is increased by a magnitude of 3, and the deep-level emissions (450-700 nm) are drastically decreased as compared with HPDs without coverings of Au NPs. Such a result increases UV-to-visible rejection ratio from 214 to 6180 and it attributes that the defect-level emissions of ZnO induce surface plasmon resonance in Au NPs and then enhances the emissions, exciting a large quantity of electrons crossing over the Au NP/ZnO interface barrier. Consequently, these electrons are transferred to the ZnO conduction band from the Au NPs, causing a photocurrent gain and the quantum efficiency is as high as 1157% at 2 V reverse bias.

Tailoring optical properties of surface charged dielectric nanoparticles based on an effective medium theory

We propose an effective-medium theory (EMT) for the surface charged dielectric nanoparticles (CDNPs) in the long wavelength limit, in which a homogenous CDNP is demonstrated to be equivalent to a conventional absorbing neutral particle of the same size but with different constitutive parameters (effective permittivity εe and effective permeability μe). It is found that while the surface charge induces negligible change of magnetic permeability in particle, it gives rise to a significant change of electric permittivity. The change in permittivity depends on the charge, the particle size, and the working frequency but is independent of the constituent material. In infrared frequencies, both the real and imaginary parts of the particle permittivity may be changed considerably by surface charging. At higher frequency, the surface charge can lead to a remarkable decrease in the real part of the permittivity while keeping its imaginary part nearly unchanged. Therefore, based on EMT we can tailor the optical properties of CDNPs by optimizing their parameters, allowing for many exotic phenomena, such as vanishing scattering efficiency, great enhancement of light absorption efficiency, and surface charge induced surface plasmon resonance.

Gold nanomesh induced surface plasmon for photocurrent enhancement in a polymer solar cell

In this study, a gold (Au) nanomesh layer was manufactured on an ITO-coated glass substrate at room temperature. The Au nanomesh was used to induce surface plasmon resonance (SPR) to enhance the photocurrent of a polymer solar cell. The Au nanomesh was manufactured by lift-off on closely packed PS nanospheres (diameter ∼50 nm; density ∼10 10/cm 2). The PS nanospheres were fabricated by modified block copolymer nano-patterning on ITO. A transmittance–reflection–absorbance spectrum was used to explore the induced surface plasmon. An extinction peak was observed at ∼580 nm indicate the possibility of Au nanomesh induced surface plasmon resonance. The short-circuit current density of the polymer solar cell was enhanced from 7.02 to 14.2 mA/cm 2 by the addition of Au nanomesh. Consequently, the power conversion efficiency enhanced from 1.9% to 3.2%. By the normalized input photon-to-current conversion efficiency (IPCE) measurement, enhanced photocurrent conversion efficiency at approximately 580 nm was observed that coincided with the extinction spectrum, indicating that the surface plasmon enhanced the photocurrent.

Photocatalytic activity of predominantly rutile mixed phase Ag/TiV oxide nanoparticles under visible light irradiation

Nanoscale synthesis of silver sensitized titanium vanadium mixed-metal (Ag/TiV) oxides was done employing sol–gel technique. The physico–chemical properties of the material were examined using XRD (X-ray diffraction), SEM (Scanning Electron Microscopy), EDAX (Energy Dispersive X-ray Spectroscopy), HR-TEM (High Resolution Transmission Electron Microscopy), XPS (X-ray Photoelectron Spectroscopy), UV-DRS and Photoluminescence analysis (PL). The results indicated the presence of predominantly rutile mixed phase particles of 20–30 nm grain size. Identically prepared TiV as well as Ag/TiV oxide catalyst showed enhanced and extended visible light absorption with an absorption upper limit, λ ≥ 550 nm. The visible light photocatalytic activity of Ag/TiV oxide showed an increase of about three and seven times compared to TiV oxide and Degussa P25 respectively, in the rate of degradation of phenol. The reason for the enhanced visible light activity of Ag/TiV oxide may be ascribed to elevated and extended absorption due to combined effect of dopant induced band gap reduction and visible light induced surface plasmon resonance of the Ag nanoparticles. The photocatalytic activity is complemented by localized charge traps and Ag assisted charge separation in the system as well.

Plasmons: Chemical Bonding Coupling Induced Surface Plasmon Resonance Splitting in Self-Assembled Gold Nanoparticles

Recently, the effect of π-bonding electrons conjugating to a gold surface has been predicated by first principles. In this paper, we observe surface plasmon resonance splitting due to the covalence and π-bonding electrons conjugated effect. When surfactantless Au NPs are linked on the glass substrate by sulfur, the SPR peak is split from one mode (638 nm) into two modes at 615 and 643 nm. The binding energy of 3s electrons for sulfur atoms has a huge red-shift in XPS peaks to confirm the π-bonding electrons conjugated effect. Furthermore, a proposed classical coupling dielectric function model, adding the gold−sulfur covalence bonding effect and conjugated π-bond electrons from sulfur to gold into the Drude model, is achieved to explain the mechanism of the SPR split phenomenon. In the extreme case, when the Au surface atoms are all covered by thiol sulfur atoms, or not covered at all by thiols, the SPR peak will not split. We found 3.28% of the Au atoms are bound by sulfur atoms and 92% of the conjugated electrons of the sulfur atoms transfer to Au electronic gas. The coverage rate of the sulfur atoms bonded to the surface of the Au atoms is about 25%, and this can cause the SPR splitting.

Numerical simulation of probe induced surface plasmon resonance coupling nanolithography

A new nanolithographic technology, the probe induced surface plasmon resonance coupling nanolithography (PSPRN), is presented and analyzed numerically by using finite difference time domain method for the loss and dispersive materials. The PSPRN uses a fundamental mode Gaussian beam with wavelength of 514.5nm to excite the Kretschmann surface plasmon resonance, and utilizes the metal probe local-field enhancement effect to realize nanolithography. The influences of different distances between probe and recording layer and different sizes of tip on local field enhancement and the distribution of electric field intensity amplitude on the surface of recording layer were investigated. Results show that the local field enhancement effect is most significant and the electric field intensity amplitude contrast ratio is maximal when the probe is in contact with the recording layer. When the distance between tip and recording layer is 5nm, the distribution width of the relative electric field intensity amplitude above the critical value for near-field nanolithography on the surface of recording layer is close to the size of the tip.

Control of the plasmon absorption of gold nanoparticles with a two-color excitation

Substantial photoinduced changes of ultraviolet (UV) -visible (UV-vis) optical spectra were observed for the Au nanoparticles prepared by a “touch” seed-mediated growth technique on the surface of indium-tin-oxide substrate. The phototreatment was performed by two-color coherent laser beams with a wavelength of 1060 nm (fundamental beam) and double frequency 530 nm (writing beam). The maximal photoinduced changes of the UV-vis spectra were observed for the surfaces possessing low resistivity (about 4Ω∕sq). Those of higher resistivity (about 50Ω∕sq) demonstrate only slight shifts of the main Au particle surface-plasmon resonance maxima at λ=570nm. The effect observed is a consequence of a superposition of optically induced surface plasmon resonance, scattering on optically induced grating and electron-phonon relaxation.

Two-photon absorption-induced [formula omitted] fluorescence of dysprosium ions

Fluorescence spectra of a solution containing Dy 3+ ions have been measured at room temperature. The excitation spectrum features show a great peak at 350 nm when the detection wavelength is fixed at 483 nm. Meanwhile another weaker peak takes place at 630 nm, which is owing to two-photon absorption. Therefore, as the excitation wavelength is fixed at 320 nm and 630 nm, respectively, both single-photon and two-photon absorption induced fluorescence emission peaks are observed. Furthermore, the emission excited by 630 nm is more intense. When silver colloids are added to the solution containing Dy 3+, the enhancements of two-photon absorption induced fluorescence are more intensive. We believe that these enhanced fluorescence are due to the local field enhancement around Dy 3+ ions owing to the induced surface plasmon resonance of silver nanoparticles.