Changes In Scattering Intensity Research Articles

Improve the Effective Resonance Light Scattering of Three-Layered Plasmonic Au@Dielectric@Ag Bimetallic Nanoshells

The strong light scattering from SPR has received an extraordinary attention due to the useful applications in photodetectors and cell and biomedical imaging. However, the applications using light scattering require a high scattering cross-section along with low absorption losses near the resonance wavelength. In this paper, effective plasmonic scattering of three-layered Au–Ag bimetallic nanoshells with a dielectric separate layer has been studied using the quasi-static approximation of classical electrodynamics. Because of the surface plasmon resonance (SPR)-induced intense light absorption, the effective scattering intensity is much weaker than that of scattering cross-section. However, the effective scattering intensity could be improved by tuning the geometric dimension and local dielectric environment of the nanostructure. It has been found that the greatest effective scattering takes place when the outer Ag nanoshell has a thick thickness or the dielectric separate layer has a small dielectric constant. The effective scattering also depends on the inner Au sphere radius and outer surrounding dielectric constant. Because of the mode transformation of the SPR, the effective scattering could also be greatly improved when the inner Au sphere has a very small or large size. However, the effective scattering intensity changes non-monotonously as the surrounding dielectric constant increases. The greatest effective scattering could be obtained when the surrounding dielectric constant has an intermediate value. This tunable effective plasmonic scattering of Au@Ag three-layered nanoshells presents a potential for design and fabrication of plasmonic optical nanodevice based on resonance light scattering.

Intensity-Based Single Particle Plasmon Sensing.

Plasmon sensors respond to local changes of their surrounding environment with a shift in their resonance wavelength. This response is usually detected by measuring light scattering spectra to determine the resonance wavelength. However, single wavelength detection has become increasingly important because it simplifies the setup, increases speed, and improves statistics. Therefore, we investigated theoretically how the sensitivity toward such single wavelength scattering intensity changes depend on the material and shape of the plasmonic sensor. Surprisingly, simple equations describe this intensity sensitivity very accurately and allow us to distinguish the various contributions: Rayleigh scattering, dielectric contrast, plasmon shift, and frequency-dependent plasmon bulk damping. We find very good agreement of theoretical predictions and experimental data obtained by single particle spectroscopy.

Structural Effects of High Hydrostatic Pressure on Human Low Density Lipoprotein Revealed by Small Angle X-ray and Neutron Scattering

Low-density lipoprotein (LDL) is the principal cholesterol transporter in the human blood circulation. The quasi-spherical LDL particles (∼20 nm) are made up of a complex combination of various lipids and a large single amphipathic protein moiety, named apolipoprotein B-100. LDL has a hydrophobic core and an amphiphilic shell. Each particle has a specific phase transition temperature (Tm) corresponding to the melting of the core lipids from an ordered liquid crystalline to a disordered fluid phase.The structural impact of high hydrostatic pressure (HHP) was studied with different types of LDL (native, oxidized and triglyceride rich) with SANS (PSI, Switzerland) and SAXS (Elettra, Italy). The HHP ranged from 50 to 3000 bar. Temperature points were chosen below, on and above Tm.The pair distance distribution functions p(r) of the SAS curves revealed pressure dependent changes of the particle structure seen in the low q-region (∼0.25 nm−1), also reflected by a decrease of Radii of Gyration (Rg) with increasing pressure.Especially the p(r) functions from the SAXS data do not only show an overall particle change but also a highly pressure sensitive inner organization. A triple-peak feature indicating the lamellar lipid organization below Tm was induced by raising the pressure up to 3000 bar. These pressure sensitive lipid layers were observed by scattering intensity changes in SAXS curves at q=1.7 nm−1.The shape alterations could be evidenced by fitting an ellipsoidal model to the SANS curves resulting in a decrease of the ellipsoidal radii under pressure. A new LDL model considering the cross-sectional electron density profile is developed and applied to the SAS data to get a more detailed insight into pressure dependent behavior.

Observation of femtosecond molecular dynamics via pump–probe gas phase x-ray scattering

We describe a gas-phase x-ray scattering experiment capable of capturing molecular motions with atomic spatial resolution and femtosecond time resolution. X-ray free electron lasers can deliver intense x-ray pulses of ultrashort duration, making them suitable to study ultrafast chemical reaction dynamics in an ultraviolet pump, x-ray probe scheme. A cell diffractometer balances sample flow with gas density and laser focusing conditions to provide adequate scattering vector resolution with high signal intensity and near-uniform excitation probability. Images from a pixel-array x-ray detector, spatially and electronically calibrated, allow for detection of scattering intensity changes below 1%. First experiments on the ring-opening reaction of 1,3-cyclohexadiene to form 1, 3, 5-hexatriene show a rapid initial reaction on an 80 fs time scale.

Detecting intrinsic scattering changes correlated to neuron action potentials using optical coherence imaging.

We demonstrate how optical coherence imaging techniques can detect intrinsic scattering changes that occur during action potentials in single neurons. Using optical coherence tomography (OCT), an increase in scattering intensity from neurons in the abdominal ganglion of Aplysia californica is observed following electrical stimulation of the connective nerve. In addition, optical coherence microscopy (OCM), with its superior transverse spatial resolution, is used to demonstrate a direct correlation between scattering intensity changes and membrane voltage in single cultured Aplysia bag cell neurons during evoked action potentials. While intrinsic scattering changes are small, OCT and OCM have potential use as tools in neuroscience research for non-invasive and non-contact measurement of neural activity without electrodes or fluorescent dyes. These techniques have many attractive features such as high sensitivity and deep imaging penetration depth, as well as high temporal and spatial resolution. This study demonstrates the first use of OCT and OCM to detect functionally-correlated optical scattering changes in single neurons.

STUDIES ON A FOUR-ARM POLYSTYRENE GEL BY LASER LIGHT SCATTERING

Atom transfer radical polymerization(ATRP)was used to synthesize narrowly distributed 4-arm-polystyrene star chains(4-PS-Br).Then the bromine end functional groups were further modified to thiol groups(4-PS-SH).Oxidization of each two thiol end groups leads to a disulfide bond(—S—S—),which enables us to slowly crosslink the PS star chains in THF solutions to form polymer clusters,then gels.Static laser light scattering(SLS)shows that in both semidilute solutions and gels the time-average scattered intensity changes little with the sample position,where the sample position is arbitrarily chosen by rotating and lifting the sample cuvette,indicating this chemical gel is homogeneous and speckle-free.Dynamic laser light scattering(DLS)shows that first there is only one fast decay mode of the time-time intensity correlation function in the original semidilute solution.Then the slow modes of the correlation function appear and the contributions of the slow modes increase at the early oxidation stage,indicating the formation of large cross-linked clusters.With oxidation time increase the contribution of the slow mode decreases,finally disappears.The correlation functions of the chemical gel are nearly the same as those of the original semidilute solution.The normalized intermediate scattering function can fully relax to zero,indicating that the gel has no frozen-in static component,and the speckles of other polymer gels originate from large voids inside,not cross-linked chains(clusters).Both SLS and DLS results indicate that this polystyrene gel is a homogeneous chemical gel.

Elastic diffuse scattering of neutrons in FeNi Invar alloys

Elastic diffuse scattering of neutrons was found around various Bragg-peak positions in FeNi Invar alloys. The diffuse scattering intensities depend on the temperature and Ni concentration. The intensities increase with decreasing temperature and decrease with increasing Ni concentration. The distribution of diffuse scattering intensity changes from peak to peak and is well explained by the formation of clusters with a lattice deformation consisting of a shear wave propagating along the $⟨1\text{ }1\text{ }0⟩$ direction and with the $⟨1\text{ }\ensuremath{-}1\text{ }0⟩$ polarization vector. The ranges of temperature and Ni concentration, for which diffuse scattering is observed, coincide with those for which the Invar anomalies are observable. The origin of the clusters together with the lattice deformation and their role with regard to the Invar effects are discussed as well as the possibility of a precursor for the fcc-bcc martensitic transformation observed in FeNi alloys.

Changes in Light Scattering Intensity of Fish Holo-, Apo- and Reconstituted Myoglobins under Thermal Denaturation

Changes in Light Scattering Intensity of Fish Holo-, Apo- and Reconstituted Myoglobins under Thermal Denaturation

Anti-phase boundaries and phase transitions in titanite; an X-ray diffraction study

X-ray diffraction rocking curves of titanite, CaTiSiO 5 , were measured using a novel high-resolution diffractometer. Three Bragg reflections were recorded as a function of temperature and their profiles analyzed in terms of a Gaussian Bragg peak and a diffuse scattering component with an overall Lorentzian shape. The temperature dependence of the Gaussian intensities of the rocking peaks of superstructure reflections, hkl with k+l odd, scale with the long-range order parameter as I infinity Q 2 infinity [T-T c ] (super 2beta ) , where beta = 0.14(1) is the effective order parameter exponent. The diffuse scattering intensity changes little with temperature at T c -20 K. Strong diffuse scattering is found at T>T c with centers of their Lorentzian diffraction profiles shifted by Delta omega nearly equal 0.5 degrees with respect to the position of the equivalent Bragg peak. A second phase transition at 825 K is confirmed and the possibility of a third transition at approximately 1150 K is discussed.

Light Scattering and Gel Inhomogeneities

Abstract Light Scattering results on polyacrylamide networks show that the scattered intensity changes as different positions of a sample are probed. The scattered intensity from gels, measured by averaging through many different positions, was found to be much larger than the intensity scattered by the equivalent polymer solution. This excess arises from the frozen-in fluctuations due to the presence of cross-links. This additional structure in gels can be enhanced or reduced with conditions of preparation. Modeling a gel by a random network of springs is presented. The resulting scattering properties mimic real gel behavior.

Kinetic study on the equilibrium between membrane-bound and free photoreceptor G-protein.

Formation of the complex between photoreceptor G-protein (G) and photoactivated rhodopsin (RM) leads to a change in the light scattering of the disk membranes (binding signal or signal P). The signal measured on isolated disks (so-called PD signal) is exactly stoichiometric in its final level to bound G-protein but its kinetics are much slower than the RMG binding reaction. In this study on isolated disks, recombined with G-protein, we analyzed the PD-signal level and kinetics as a function of flash intensity and compared it to the RMG-complex formation monitored spectroscopically (by extra metarhodopsin II). The basic observation is that the initial slopes of the PD signals decrease with flash intensity when the signals are normalized to the same final level. This finding prevents an explanation of the scattering signal by a slow postponed reaction of the RMG complex. We propose to interpret the scattering change as a redistribution of G-protein between a membrane-bound and a solved state. The process is driven by the complexation of membrane-bound G to flash-activated rhodopsin (RM). The experimental evidence for this two-state model is the following: The intensity dependence of the initial rate of the PD signal is explained by the model. Under the assumption of a bimolecular reaction of free G with sites at the membrane, equal to rhodopsin in their concentration, the measured rates yield a KD of 10(-5) M. Evaluation of the extra MII kinetics yields a biphasic rise at saturating flashes. The measured rates fit to the supply of free and membrane-bound G-protein for the reaction with RM. Quantitative estimation of the expected scattering intensity changes gives a comprehensive description of binding signal and dissociation signal by the gain and loss of G-protein scattering mass. The temperature dependence of the PD-signal rate leads to an activation energy of the membrane-association process of E alpha = 44 kJ/mol.

Osmotic swelling of unilamellar vesicles by the stopped-flow light scattering method. Influence of vesicle size, solute, temperature, cholesterol and three α,ω-dihydroxycarotenoids

α,ω-Dihydroxycarotenoids are postulated to play the rôle of membrane reinforcers in certain procaryotes, like cholesterol in eucaryotes. In order to evaluate the rigidifying effect of these polyterpenoids on lipid bilayers, osmotic swelling of unilamellar vesicles has been followed by measuring the light scattering intensity changes in a stopped-flow apparatus. A model based upon the Rayleigh-Gans theory was developped. It shows that the variation of light scattering intensity ( ΔI I 0 ) is proportional to that of vesicle radius ( ΔR R 0 ) for a given R 0 (initial vesicle radius). An emperical relationship between −ΔI I 0 and Z (dissymmetry measured by light scattering) was established: −ΔI I 0 is proportional to ( Z − 1). Therefore, the value −ΔI (I 0 · (Z − 1)) is independent of vesicle radius and can be used for the evaluation of bilayer rigidity. The water permeability was measured and it was shown that it is the limiting factor of the kinetics of swelling. When incorporated into dimyristoylphophatidylcholine vesicles, cholesterol and α,ω-dihydroxycarotenoids lower the water permeability and the value of −ΔI (I 0 · (Z − 1)) . So, at least on model systems, α,ω-dihydroxycarotenoids exert on a phospholipid bilayer a reinforcement effect similar to cholesterol.

A study of the kinetics and mechanism of ADP-triggered platelet aggregation

The time-course of ADP-triggered aggregation of human blood platelets has been followed by sensitive right-angle light scattering intensity measurements as a function of the platelet and fibrinogen concentrations. Rayleigh-Gans light scattering theory has been combined with the Smoluchowski aggregation model to predict the dependence of the right-angle scattering intensity on particle size and concentration as well as the time-dependent changes during aggregation. The validity of the calculations was confirmed by measuring the scattering intensity with suspensions of polystyrene microspheres of known radius, as well as the time-dependent changes in the 90° scattering intensity during aggregation of these particles. However, in contrast to the predictions of the model, the time-course of the scattering intensity changes during platelet aggregation was characterized by single exponential decay with a rate constant which reached a limiting value of 0.017 s −1 at high platelet concentrations. The value of k agg was also independent of the fibrinogen concentration over a 30-fold range. Covalently cross-linked fibrinogen dimers and Fragment D-inhibited fibrin protofibrils yielded aggregation rates that agreed with those measured with fibrinogen. The results indicate that the rate of platelet aggregation is not limited by either the rate of fibrinogen binding or the frequency of platelet-platelet collisions under these conditions.

Transient light scattering from halloysite suspensions

A study is reported on a dilute aqueous suspension of the hollow rod particles of halloysite. Transient changes in the scattered intensity, which are quick and easy to record, during the application of pulsed electric fields to the suspension, have been used to evaluate particle lengths ( L) of the order of 920 nm. Furthermore, by varying the frequency of the applied electric field, the frequency dependent dispersion of the scattered intensity changes ( ΔI) could be obtained. It is shown that the initial decay of the transient intensity changes indicate, under specific conditions, length parameters for the rods which are close to the Z and ( Z + 1) averages when compared with Zimm plot and electron microscopic data. With high frequency fields, an electric polarisability of 14 × 10 −29 Fm 2 was obtained. This is attributed primarily to interfacial origins. The frequency dispersion of ΔI was characterized through a critical frequency of 33 Hz corresponding to a particle length of only 315 nm. Although present in the electron histograph of sizes, this value corresponds to a very low average length parameter, well below the number average length of 617 nm. The dispersion was also indicative of a permanent dipole moment across the major cyclinder axis when using a Debye-type relaxation equation. The existence of such a vector property transverse to the axis of a symmetric cylinder is questioned.

Transient scattering from absorbing solutions

Although light scattering has become a standard method for determining the geometric parameters of macromolecular solutes in solution, it has serious theoretical and experimental limitations when the solutions partly absorb the incident light. When subjected to pulsed electric fields, electrically anisotropic molecules orientate. This changes the scattered intensity. By making measurements of the relative scattered intensity changes as the molecules revert to a random array after the electric pulse has ceased, the molecular relaxation times, and hence the molecular dimensions, may be evaluated whether or not the material is absorbing. Typical measurements are made on vanadium pentoxide and benzopurpurine suspensions and tobacco mosaic virus solutions at a variety of wavelengths to demonstrate the method.

Electro-optic scattering from solutions of poly( n-hexyl) isocyanate

Results are reported of a study on the intensity of the light scattered from solutions of a sample of n-hexyl poly isocyanate in tetrahydrofuran. Measurements were made both prior to and during the application of alternating electric fields to the solutions. In the absence of these fields, the molecules were characterized by a weight average mol. wt. of 2·8 × 10 6 and a Z average radius of gyration of 290 nm. Electric fields of up to 900 V cm −1 intensity, and frequencies up to 2·5 kHz were then applied to the solutions. The scattered intensity changes indicated that the rod-like molecules behaved as if they were rigid, with both permanent and induced dipole moments predominantly along the major rod axis. These properties arose from an overall permanent moment of 29 × 10 3 D and a difference of electrical anisotropies ( α 1 − α 2) of 9·2 × 10 3 D units. The molecular rotary diffusion coefficient of 790 sec −1 was also determined. Upon analysis, this gave information about the polydispersity of the sample. It was concluded that the experimental procedure, described herein, provided abundant information about the molecular parameters of the polymer, and that in general it would be very suitable for such characterization studies provided that the solute molecules were large enough in their major dimension as to be comparable to the wavelength of the incident light.