Surface Plasmon Resonance Energy Research Articles

Influence of Fe2+ and Ni2+ contents on the optical and electrical properties of ZnS quantum dots

The work reports a well controlled synthesis of un-doped and Fe2+ and Ni2+ doped ZnS quantum dots (QDs) based highly luminescent of pure cubic zinc blende structure. The samples were characterized for structural, morphological, optical and electrical parameters and great care has been made in correlating all these properties. The optimum concentrations of Zn1−xFexS and Zn1−xNixS dopants were found to be x = 0.2 for superior optical and electrical properties. Incorporation of Fe2+ or Ni2+ into ZnS lattice have generated acceptor level as an isolated state just above the valence band of ZnS, and hence electron requiring less excitation energy for transferring from the acceptor level to the conduction band. Moreover, it was found that the PL emission intensity of Fe2+ doped ZnS QDs is higher than that of Ni2+ doped. The results indicated that the active luminescent centers created by dopants and localized surface plasmon resonance energy transfer of ZnS QDs significantly increased with Fe2+ ions into the ZnS lattice. Over all in light of the results obtained during the study, the doped samples can have potential for function in vast variety of applications.

(Invited) Silicon-Based Nano-Composites Made from All-Inorganic Colloidal Silicon Nanocrystals

Silicon (Si) nanocrystals have been a subject of intensive research for many years as nanoscale luminescence materials. In particular, the research on colloidal form Si nanocrystals are growing rapidly in recent years, because of the versatility in many kinds of applications. Recently, we have developed a new type of all-inorganic Si nanocrystals that can be dispersed in alcohol and water almost perfectly without any surface functionalization processes. The unique property arises from the core-shell structure. The shell is very heavily boron (B) and phosphorus (P) doped crystalline Si, which induces negative potential on the surface and prevents the agglomeration in polar solvents. The B and P codoped Si nanocrystals have several characteristic properties not being observed in usual Si nanocrystals. Among them, an important feature is the insensitiveness of the luminescence property to environment and to chemical treatment of the surface. Because of the insensitiveness, the codoped Si nanocrystals are a very suitable material for the production of a variety of Si nanocrystal-based nanocomposites. In this work, we first discuss structural and optical properties of B and P codoped colloidal Si nanocrystals, and then show the luminescence properties of dense solids made from the colloidal Si nanocrystals. We discuss the effects of the dielectric environment and the energy transfer between nanocrystals on the luminescence properties of Si nanocrystal solids. We also produce composite nanopartciles consisting of codoped Si nanocrystals and gold (Au) nanoparticles or nanorods. We demonstrate the enhancement of the radiative decay rate and quantum yield of Si nanocrystals by tuning the surface plasmon (SP) resonance energy to the luminescence energy. We also show the excitation cross-section enhancement, when the SP resonance energy coincides with the excitation energy.

Resonant surface-enhanced Raman scattering by optical phonons in a monolayer of CdSe nanocrystals on Au nanocluster arrays

Here we present the results on an investigation of resonant Stokes and anti- Stokes surface-enhanced Raman scattering (SERS) by optical phonons in colloidal CdSe nanocrystals (NCs) homogeneously deposited on arrays of Au nanoclusters using the Langmuir–Blodgett technology. The thickness of deposited NCs, determined by transmission and scanning electron microscopy, amounts to approximately 1 monolayer. Special attention is paid to the determination of the localized surface plasmon resonance (LSPR) energy in the arrays of Au nanoclusters as a function of the nanocluster size by means of micro-ellipsometry. SERS by optical phonons in CdSe NCs shows a significant enhancement factor with a maximal value of 2×103 which depends resonantly on the Au nanocluster size and thus on the LSPR energy. The deposition of CdSe NCs on the arrays of Au nanocluster dimers enabled us to study the polarization dependence of SERS. It was found that a maximal SERS signal is observed for the light polarization along the dimer axis. Finally, SERS by optical phonons was observed for CdSe NCs deposited on the structures with a single Au dimer. A difference of the LO phonon energy is observed for CdSe NCs on different single dimers. This effect is explained as the confinement-induced shift which depends on the CdSe nanocrystal size and indicates quasi-single NC Raman spectra being obtained.

Individual and collective modes of surface magnetoplasmon in thiolate-protected silver nanoparticles studied by MCD spectroscopy.

Large magneto-optical (MO) responses at the energy of localized surface plasmon resonance (LSPR), namely, surface magnetoplasmons, are demonstrated for the first time in thiolate-protected silver nanoparticles with magnetic circular dichroism (MCD) spectroscopy. The samples examined are decanethiol (DT)-, azobenzenethiol (ABT)-, and ABT/DT mixed-monolayer-protected Ag nanoparticles. ABT-protected Ag nanoparticles are somewhat aggregated and thus exhibit a broad, collective mode of plasmonic absorption, whereas other samples with highly-dispersed nanoparticles show an individual mode of LSPR absorption. In all Ag nanoparticles, a derivative-like MCD signal is observed under an applied magnetic field of 1.6 T, which can be explained in terms of two circular modes of magnetoplasmon caused by the increase (or decrease) in the Lorentz force imparted on the free electrons that oscillate in the left (or right) circular orbits in the nanosphere. For the Ag nanoparticles exhibiting an individual LSPR mode, in particular, simultaneous deconvolution analysis of UV-vis absorption and MCD spectra reveal that (i) the amplitude of the magnetoplasmonic component with lower frequency (ω-), resulting from the reduction in the confinement strength of collective electrons by the Lorentz force, is stronger than that with a higher frequency (ω+); (ii) the accurate shift or cyclotron frequency between two magnetoplasmonic modes (ωc = ω+-ω-) is size-dependent, and presents a very large value with implications for the apparent enhancement of the local magnetic-field in the Ag nanoparticles. These results strongly suggest that the Ag-thiolate layer or Ag-S bonding on the nanoparticle surface plays a significant role in the MO enhancement.

Effects of silver nanoparticles on Raman spectrum and fluorescence enhancement of nano-diamond

The nano-diamond has been a hot topic in the field of nano-science and nanotechnology for its optical properties. Much effort has been devoted to improving the fluorescence and Raman scattering intensity of nitrogen-vacancy (NV) center in nano-diamond by using plasmon resonance effect in sensing area. A combination of Ag nanoparticle and diamond can not only take advantage of the stability and biocompatibility of diamond, but also enhance the local electric field around NV center through the Ag nanoparticles, thereby speeding up the radiation of the fluorescent near the surface of the substrate, improving the strength and stability of the fluorescence, and greatly broadening the application areas of Raman spectroscopy. In this paper, we mix the nano-diamonds with Ag nanoparticles to improve the fluorescence and Raman scattering intensity on the basis of the localized surface plasmon resonance effect. The influences of Ag mass concentration on the Raman spectrum and fluorescence intensity are investigated. The results show that when the concentration of nano-Ag nanoparticles reaches up to 5 wt%, the light intensity becomes saturated, but the concentration further increases up to a value more than 7 wt% the light intensity begins to decline. Then the corresponding radiative transition rate and the fluorescence quantum efficiency are investigated, and based on these researches, influences and mechanism of surface plasmon resonance (SPR) enhancement are discussed thoroughly. We deduced that the fluorescence enhancement is mainly due to the enhanced surface plasmon field caused by transfer of surface plasmon resonance energy and the energy transfer between surface plasmon and excited state of NV centers. When the concentration of Ag nanoparticles reaches an appropriate value, a suitable distance between metal nanoparticles and diamond is obtained, thereby ensuring the strong local electric field forming on the metal surface, accelerating the emitting photons of diamond in the excited state, and also suppressing the transfer of non-radiative energy, eventually leading to the increase of diamond fluorescence emission intensity.

Surface-enhanced Raman scattering by colloidal CdSe nanocrystal submonolayers fabricated by the Langmuir-Blodgett technique.

We present the results of an investigation of surface-enhanced Raman scattering (SERS) by optical phonons in colloidal CdSe nanocrystals (NCs) homogeneously deposited on both arrays of Au nanoclusters and Au dimers using the Langmuir–Blodgett technique. The coverage of the deposited NCs was less than one monolayer, as determined by transmission and scanning electron microscopy. SERS by optical phonons in CdSe nanocrystals showed a significant enhancement that depends resonantly on the Au nanocluster and dimer size, and thus on the localized surface plasmon resonance (LSPR) energy. The deposition of CdSe nanocrystals on the Au dimer nanocluster arrays enabled us to study the polarization dependence of SERS. The maximal SERS signal was observed for light polarization parallel to the dimer axis. The polarization ratio of the SERS signal parallel and perpendicular to the dimer axis was 20. The SERS signal intensity was also investigated as a function of the distance between nanoclusters in a dimer. Here the maximal SERS enhancement was observed for the minimal distance studied (about 10 nm), confirming the formation of SERS “hot spots”.

Interaction of βA3-Crystallin with Deamidated Mutants of αA- and αB-Crystallins.

Interaction among crystallins is required for the maintenance of lens transparency. Deamidation is one of the most common post-translational modifications in crystallins, which results in incorrect interaction and leads to aggregate formation. Various studies have established interaction among the α- and β-crystallins. Here, we investigated the effects of the deamidation of αA- and αB-crystallins on their interaction with βA3-crystallin using surface plasmon resonance (SPR) and fluorescence lifetime imaging microscopy-fluorescence resonance energy transfer (FLIM-FRET) methods. SPR analysis confirmed adherence of WT αA- and WT αB-crystallins and their deamidated mutants with βA3-crystallin. The deamidated mutants of αA–crystallin (αA N101D and αA N123D) displayed lower adherence propensity for βA3-crystallin relative to the binding affinity shown by WT αA-crystallin. Among αB-crystallin mutants, αB N78D displayed higher adherence propensity whereas αB N146D mutant showed slightly lower binding affinity for βA3-crystallin relative to that shown by WT αB-crystallin. Under the in vivo condition (FLIM-FRET), both αA-deamidated mutants (αA N101D and αA N123D) exhibited strong interaction with βA3-crystallin (32±4% and 36±4% FRET efficiencies, respectively) compared to WT αA-crystallin (18±4%). Similarly, the αB N78D and αB N146D mutants showed strong interaction (36±4% and 22±4% FRET efficiencies, respectively) with βA3-crystallin compared to 18±4% FRET efficiency of WT αB-crystallin. Further, FLIM-FRET analysis of the C-terminal domain (CTE), N-terminal domain (NTD), and core domain (CD) of αA- and αB-crystallins with βA3-crystallin suggested that interaction sites most likely reside in the αA CTE and αB NTD regions, respectively, as these domains showed the highest FRET efficiencies. Overall, results suggest that similar to WT αA- and WTαB-crystallins, the deamidated mutants showed strong interactionfor βA3-crystallin. Variable in vitro and in vivo interactions are most likely due to the mutant’s large size oligomers, reduced hydrophobicity, and altered structures. Together, the results suggest that deamidation of α-crystallin may facilitate greater interaction and the formation of large oligomers with other crystallins, and this may contribute to the cataractogenic mechanism.

Synthesis of Photoswitchable Magnetic Au-Fullerosome Hybrid Nanomaterials for Permittivity Enhancement Applications.

We designed and synthesized several nanomaterials 3 of three-layered core-shell (γ-FeOx@AuNP)@[C60(>DPAF-C9)1or2]n nanoparticles (NPs). These NPs having e−-polarizable fullerosome structures located at the outer layer were fabricated from highly magnetic core-shell γ-FeOx@AuNPs. Fullerosomic polarization of 3 was found to be capable of causing a large amplification of material permittivity that is also associated with the photoswitching effect in the frequency range of 0.5‒4.0 GHz. Multilayered synthetic construction allows Förster resonance energy transfer (FRET) of photoinduced accumulative surface plasmon resonance (SPR) energy in the gold layer to the partially bilayered C60(>DPAF-C9)1or2-derived fullerosome membrane shell layer in a near-field of direct contact without producing radiation heat, which is commonly associated with SPR.

Tuning Localized Surface Plasmon Resonance in Scanning Near-Field Optical Microscopy Probes.

A reproducible route for tuning localized surface plasmon resonance in scattering type near-field optical microscopy probes is presented. The method is based on the production of a focused-ion-beam milled single groove near the apex of electrochemically etched gold tips. Electron energy-loss spectroscopy and scanning transmission electron microscopy are employed to obtain highly spatially and spectroscopically resolved maps of the milled probes, revealing localized surface plasmon resonance at visible and near-infrared wavelengths. By changing the distance L between the groove and the probe apex, the localized surface plasmon resonance energy can be fine-tuned at a desired absorption channel. Tip-enhanced Raman spectroscopy is applied as a test platform, and the results prove the reliability of the method to produce efficient scattering type near-field optical microscopy probes.

The effect of plasmonic near field tuning on spontaneous emission intensity of dual emitting ZnO:Er3+ nanoparticles

The effect of plasmonic near field of silver nanoparticles (Ag NPs) on luminescence of Er3+ doped ZnO nanoparticles that exhibit dual mode excitation has been investigated. The surface plasmon resonance (SPR) energy is shown to play an important role in optical enhancements (under UV excitation) and quenching (under IR excitation) in ZnO:Er3+ NPs optimally conjugated with Ag NPs. Enhancement of total luminescence yield by 420% from ZnO:Er3+ NPs has been realized due to proximity of Ag NPs under UV excitation. The near field generated by exact Ag NP and their extinction properties were simulated through Finite difference time domain method and a direct correlation with observed fluorescence enhancement as well as quenching could be established.

Control of localized surface plasmon resonance energy in monolayer structures of gold and silver nanoparticles.

Monolayer structures of Au and Ag nanoparticles (NPs) were fabricated by a dipping method to realize the control of localized surface plasmon resonance (LSPR) energy. The mean inter-particle distance in the monolayer was controlled by changing the concentration of NPs in the colloidal solution used for the monolayer assembly. The extinction-peak energy of the monolayer structure was red-shifted with decreasing inter-particle distance, reflecting plasmon coupling between NPs.

Role of Symmetry in Coupled Localized Surface Plasmon Resonance of a Nanosphere Pair

We investigated localized surface mode resonance of two nanospheres immersed in a continuum dielectric medium within the framework of quasistatic approximation. We solved the Laplace equation in the bispherical coordinates subjected to the boundary conditions on both spheres. By using the matrix formulation, new method for surface mode resonance calculation is derived in terms of a nonlinear eigenvalue problem. This allows us to discuss the effects of symmetry breaking due to the difference in particle materials and particle sizes. We calculated the surface plasmon resonance (LSPR) energy for pairs of Drude metallic spheres. The solutions show that the LSPR coupling in an asymmetric pair can be interpreted as the coupling between symmetric pairs of its constituent particles. we also analyzed the LSPR excitation sequence to identify the modes of peaks from optical measurement. We found that the ambiguous dipole antibonding sigma mode of the asymmetric Au-Ag pair in the experimental work (Sheikholeslami et al., Nano Lett 10(7):2655–2660, 2010) must be the quadrupole bonding sigma mode.

Exploring interaction of TNF and orthopoxviral CrmB protein by surface plasmon resonance and free energy calculation.

Inhibition of the activity of the tumor necrosis factor (TNF) has become the main strategy for treating inflammatory diseases. The orthopoxvirus TNF-binding proteins can bind and efficiently neutralize TNF. To analyze the mechanisms of the interaction between human (hTNF) or mouse (mTNF) TNF and the cowpox virus N-terminal binding domain (TNFBD-CPXV), also the variola virus N-terminal binding domain (TNFBD-VARV) and to define the amino acids most importantly involved in the formation of complexes, computer models, derived from the X-ray structure of a homologous hTNF/TNFRII complex, were used together with experiments. The hTNF/TNFBD-CPXV, hTNF/TNFBD-VARV, mTNF/TNFBD-CPXV, and mTNF/TNFBD-VARV complexes were used in the molecular dynamics (MD) simulations and MM/GBSA free energy calculations. The complexes were ordered as hTNF/TNFBD-CPXV, hTNF/TNFBD-VARV, mTNF/TNFBD-CPXV and mTNF/TNFBD-VARV according to increase in the binding affinity. The calculations were in agreement with surface plasmon resonance (SPR) measurements of the binding constants. Key residues involved in complex formation were identified.

Improved efficiency in polymer light-emitting diodes using metal-enhanced fluorescence

Metal-enhanced fluorescence was realized in the emissive layer of organic electroluminescent devices. Core-shell Au nanoparticles (Au@SiO2) doped into the emissive layer of polymer light-emitting diodes (PLEDs) were used to enhance the luminous efficiency by a factor of 1.6 relative to the undoped reference devices (from 6.3 cd/A to 10.0 cd/A). The silica shell outside the Au nanoparticles was used to ensure that there was sufficient distance between the Au nanoparticles and the fluorescent polymer material to avoid quenching of the excitons. In addition, sufficient overlap of the energy of the localized surface plasmon resonance of the Au nanoparticles and the energy of the excitons formed in the emissive layer was guaranteed. These led to an enhanced PLED efficiency. This research provides a way to obtain high performance organic electroluminescent devices.

The dipeptide H-Trp-Glu-OH (WE) shows agonistic activity to peroxisome proliferator-activated protein-α and reduces hepatic lipid accumulation in lipid-loaded H4IIE cells

Dipeptides digested from dietary proteins can be directly absorbed by the intestine and delivered to the circulatory system. However, the dipeptides’ metabolic roles and biological activities are largely unknown. Lipid-loaded HII4E cells stimulated with H-Trp-Glu-OH (WE) exhibited reduced lipid accumulation, of which the effect was abolished by peroxisome proliferator-activated receptor (PPAR) α gene knock down. A luciferase assay showed that the WE dipeptide induced PPARα transactivation in a dose-dependent manner. Surface plasmon resonance and time-resolved fluorescence resonance energy transfer analyses demonstrated that WE interacts directly with the PPARα ligand binding domain (KD, 120μM; EC50, 83μM). Cells stimulated with WE induced PPARα and its responsive genes and increased cellular fatty acid uptake. In conclusion, WE reduces hepatic lipid accumulation in lipid-loaded hepatocytes via the activation of PPARα by a direct interaction.

Observation of Surface-Enhanced Raman Scattering from Strongly Coupled Molecules and Localized Surface Plasmons in Resonance

The photoexcitation characteristics of materials have been investigated using surface enhanced Raman scattering (SERS) [1]. Signal enhancement by< 104 times of magnitude is caused by resonances that are induced by optical absorption. Previously documented studies have found that the absorption spectra of chromophores that were adsorbed to Au or Ag plasmonic nanoparticles can be strongly perturbed. This perturbation of the electronic transition should affect the SERS profiles in ways that differ from those predicted based on simple enhancement of the local electromagnetic field. Previously documented studies discussed about the SERS effect as involving transition dipole coupling between the chromophore and the metal, and also theoretical simulation including resonance coupling between the molecular electronic transition and the optical transition of the nanoparticles. Despite these attempts to research the Raman characteristics when the system achieved hybridized states, the Raman features in the strong coupling regime when using LSPR have not been clarified yet.In this study, polarized Raman scattering measurement was carried out using a hybridized system of Ag nano-dimer structures and organic dye molecules. Tuning of the localized surface plasmon resonance energy leads to modulation of the hybridized polariton energy. The anti-crossing behavior of the polariton energy implies a strong coupling regime with maximum Rabi splitting energy of 385 meV. The observation proves the effective Raman enhancement via the excitation of the upper and the lower blanches of the hybridized states at the gap of the metal dimer. Maximum Raman enhancement was obtained at an optimized resonant energy between the hybrid states and Raman excitation. Reference [1] M. Takase, F. Nagasawa, H. Nabika, K. Murakoshi, “Single Molecule Surface-Enhanced Raman Scattering as a Probe for Adsorption Dynamics on Metal Surfaces", in Frontiers of Surface-Enhanced Raman Scattering: Single-Nanoparticles and Single Cells, Y. Ozaki, K. Kneipp, and R. P. Aroca, John Wiley & Sons, New York, (2014).//

Raman Enhancement via Polariton States Produced by Strong Coupling between a Localized Surface Plasmon and Dye Excitons at Metal Nanogaps.

Polarized Raman scattering measurement was carried out using a hybridized system of Ag nanodimer structures and organic dye molecules. Tuning of the localized surface plasmon resonance energy leads to modulation of the hybridized polariton energy. The anticrossing behavior of the polariton energy implies a strong coupling regime with maximum Rabi splitting energy of 0.39 eV. The observation proves the effective Raman enhancement via the excitation of the upper and the lower branches of the hybridized states at the gap of the metal dimer. Maximum Raman enhancement was obtained at an optimized resonant energy between the hybrid states and Raman excitation.

Blueshift of the surface plasmon resonance in silver nanoparticles: substrate effects

We study the blueshift of the surface plasmon (SP) resonance energy of isolated Ag nanoparticles with decreasing particle diameter, which we recently measured using electron energy loss spectroscopy (EELS) [1]. As the particle diameter decreases from 26 down to 3.5 nm, a large blueshift of 0.5 eV of the SP resonance energy is observed. In this paper, we base our theoretical interpretation of our experimental findings on the nonlocal hydrodynamic model, and compare the effect of the substrate on the SP resonance energy to the approach of an effective homogeneous background permittivity. We derive the nonlocal polarizability of a small metal sphere embedded in a homogeneous dielectric environment, leading to the nonlocal generalization of the classical Clausius-Mossotti factor. We also present an exact formalism based on multipole expansions and scattering matrices to determine the optical response of a metal sphere on a dielectric substrate of finite thickness, taking into account retardation and nonlocal effects. We find that the substrate-based calculations show a similar-sized blueshift as calculations based on a sphere in a homogeneous environment, and that they both agree qualitatively with the EELS measurements.

Visible Light Photo-oxidation in Au Nanoparticle Sensitized SrTiO3:Nb Photoanode

Au nanoparticle decorated SrTiO3:Nb (Au/SrTiO3:Nb) has been demonstrated as a photoanode for photo-oxidation under visible light. The visible light photo-oxidation is a result of the generation of the hot electrons in the Au nanoparticles, which are subsequently injected into the SrTiO3:Nb conduction band. This leaves behind holes for electrochemical oxidation, which can oxidize a variety of chemical species with redox potentials ranging from 0 to 1.23 V vs RHE. The visible light response is most enhanced at the surface plasmon resonance energy of the Au nanoparticles, which we believe reflect the high optical density near the plasmon resonance for the sensitization. This work demonstrates a general route to impart visible light utilization to a wide band gap semiconductor for various energy conversion and environmental applications, including solar fuel generation and organic pollutant decomposition.

Cyanidin, a natural flavonoid, is an agonistic ligand for liver X receptor alpha and beta and reduces cellular lipid accumulation in macrophages and hepatocytes

Cyanidin, a natural flavonoid abundant in fruits and vegetables, is known to regulate cellular lipid metabolism; however, its underlying mechanism of action and protein targets remain unknown. Here, the ligand binding activity of cyanidin on liver X receptors (LXRs) was investigated utilizing surface plasmon resonance and time-resolved fluorescence energy transfer (TR-FRET) analyses. LXRs are nuclear receptors which function as critical transcription factors in the regulation of cellular lipid and glucose metabolism. This includes the stimulation of high-density-lipoprotein synthesis and activation of reverse cholesterol transport. The present findings show that cyanidin induces the transactivation of LXRs and binds directly to the ligand-binding domain of both LXRα and LXRβ with dissociation constants of 2.2 and 73.2μM, respectively. Cell-free FRET analysis demonstrated that cyanidin induces the recruitment of co-activator peptide for LXRα and LXRβ with EC50 of 3.5μM and 125.2μM, respectively. In addition, intracellular cholesterol and triglyceride (TG) concentrations were reduced in macrophages following cyanidin stimulation. In cultured hepatocytes, cyanidin mildly induced SREBP1c gene expression but marginally affected cellular TG concentrations as well as reduced cellular cholesterol accumulations which activated the expression of genes for reverse cholesterol transport. Two cyanidin metabolites, procatechic acid and phloroglucinaldehyde, did not directly bind or activate LXRs. These results demonstrate that cyanidin is a direct ligand for both LXRα and LXRβ, suggesting that cyanidin may operate, at least in part, through modulation of cellular LXR activity.