Light-scattering Properties Research Articles

Giant unilamellar vesicles (GUVs) as a new tool for analysis of caspase-8/Bid-FL complex binding to cardiolipin and its functional activity

Cardiolipin (CL) has recently been shown to be both an anchor and an essential activating platform for caspase-8 on mitochondria. These platforms may be at the mitochondrial contact sites in which truncated Bid (tBid) has been demonstrated to be located. A possible role for CL is to anchor caspase-8 at contact sites (between inner and outer membranes), facilitating its self-activation, Bid-full length (FL) cleavage, tBid generation (and Bax/Bak activation and oligomerization), mitochondrial destabilization and apoptosis. We have developed an in vitro system that mimics the mitochondrial membrane contact site platform. This system involves reconstituting caspase-8, Bid-FL and CL complexes in giant unilamellar vesicles (GUVs). We first validated the system by flow cytometry analysis of light-scattering properties and nonyl acridine orange staining of their CL content. Then, we used flow cytometry analysis to detect the binding of active caspase-8 to CL and the subsequent truncation of bound Bid-FL. The tBid generated interacts with CL and induces GUV breakage and partial re-vesiculation at a smaller size. Our findings suggest an active role for mitochondrial membrane lipids, particularly CL, in binding active caspase-8 and providing a docking site for Bid-FL. This phenomenon was previously only poorly documented and substantially underestimated.

Shape modeling of mineral dust particles for light-scattering calculations using the spatial Poisson–Voronoi tessellation

We present a shape model of mineral dust particles for use in light-scattering calculations. A spatial Poisson–Voronoi tessellation was applied to simulate the aggregate structure and, therefore, the rough surface of the mineral particles. To develop the shape model, we took into account statistics of shape parameters derived from the cross-sectional areas, maximum dimensions, and perimeters of field-collected dust particles. Light-scattering properties of the modeled Voronoi aggregates were examined by the finite-difference time-domain (FDTD) method. The results of randomly oriented scattering properties agreed with previously reported laboratory measurements of mineral dust particles.

SU‐GG‐T‐353: Light Scattering Properties of EBT/EBT2 Radiochromic Films and Its Application in Radiation Dosimetry

Purpose: EBT/EBT2 film has been used as a point dosimeter. Some spatial variation in sensitivity has been observed, possibly due to variation in active layer thickness. Although it is well known that EBT/EBT2 films scatter light, the light scattering has not been directly studied and is not explicitly utilized in measurements. Since the amount of scattered light may be related to the thickness of the active layer and thus the sensitivity of the film to radiation, we attempt to quantify the angular distribution of light scattered from the film and the variation of this distribution within a batch of the film sample. Method and Materials: We used a Panasonic Lumix DMC‐GF1 digital camera body as the light detector. The sensor of this camera was exposed and was very accessible when the lens was removed. A 1 mm hole was drilled on the camera body cap to define the aperture for the incident light. The film sample was placed behind the 1 mm aperture facing the light sensor of the camera. Data were obtained with the film in landscape and portrait orientations. We used a red LED at 626 nm, and a blue LED at 430 nm as light sources. They were mounted at 25 cm from the aperture. The red pixel images and blue pixel images from the camera were extracted from the raw images with dcraw and analyzed with ImageJ. Results: Light scattering was observed on EBT/EBT2 films for red and blue light. The angular scattering showed significant anisotropy which followed the film orientation as the films were rotated. Quantitative analysis of the light scatter will be reported. Conclusion: Angular distribution of light scatter from EBT/EBT2 film can be measured with a consumer digital camera. There is significant anisotropy in the scattered light distribution.

Digital Scanned Laser Light Sheet Fluorescence Microscopy

Modern applications in the life sciences are frequently based on in vivo imaging of biological specimens, a domain for which light microscopy approaches are typically best suited. Often, quantitative information must be obtained from large multicellular organisms on the cellular or even subcellular level and with a good temporal resolution. However, this usually requires a combination of conflicting features: high imaging speed, low photobleaching, and low phototoxicity in the specimen, good three-dimensional (3D) resolution, an excellent signal-to-noise ratio, and multiple-view imaging capability. The latter feature refers to the capability of recording a specimen along multiple directions, which is crucial for the imaging of large specimens with strong light-scattering or light-absorbing tissue properties. An imaging technique that fulfills these requirements is essential for many key applications: For example, studying fast cellular processes over long periods of time, imaging entire embryos throughout development, or reconstructing the formation of morphological defects in mutants. Here, we discuss digital scanned laser light sheet fluorescence microscopy (DSLM) as a novel tool for quantitative in vivo imaging in the post-genomic era and show how this emerging technique relates to the currently most widely applied 3D microscopy techniques in biology: confocal fluorescence microscopy and two-photon microscopy.

A Reporter of UV Intensity Delivered to the Cytosol during Photolytic Uncaging

Photolytic uncaging of biologically-active molecules within cells is a powerful technique. However, the delivery of uncaging light into the cytosol can vary between cell types, individual cells of the same type, and different loci within an individual cell because of optical differences in absorbance and light-scattering properties of the cytoplasm. Here, we demonstrate a simple technique for monitoring the magnitude of cytosolic ultraviolet delivery during uncaging, which also leaves a quantitative and persistent record of this within the cells. The simple method shown here provides a much needed universal monitor of the delivery of ultraviolet light to molecules within the cytosol, providing a much needed parameter for the correct interpretation of uncaging experiments.

Validity criteria of the discrete dipole approximation

There are two widely accepted restrictions on the application of the discrete dipole approximation (DDA) in the study of light scattering by particles comparable to the wavelength: (1) when considering dielectric particles, the size of the cells must satisfy the condition kd|m|<0.5, where k is the wavenumber, d is the size of the cells, and m is the complex refractive index of the constituent material and (2) when considering conductive particles, the size of the cells must be small enough to reproduce sufficiently the evolution of the electromagnetic field in the skin layer. We examine both restrictions when the DDA is applied to irregularly shaped particles and show that its restrictions are not as strong as is widely accepted. For instance, when studying irregularly shaped particles averaged over orientations, even at kd|m|=1, the DDA provides highly accurate numerical results. Moreover, we show that the impact of using large constituent cells is similar to that produced by surface roughness; therefore, the replacement of the target particle by an array of large constituent cells has the same effect, qualitatively, as incorporating additional small-scale surface roughness on the particle. Such a modification of the target particle can be desirable in many practical applications of DDA when irregularly shaped particles are considered. When applying DDA to conductive, nonspherical particles, the insufficient description of the electromagnetic field in the skin layer does not lead to a violation of the Maxwell equations, although it has a visible but nonmajor influence on the light-scattering properties of the target.

Plasmon Resonance Spectroscopy of Gold-in-Gallium Oxide Peapod and Core/Shell Nanowires

Light-scattering properties of individual gold-in-Ga(2)O(3) peapod nanowires and gold-in-Ga(2)O(3) core/shell nanowires were investigated by optical dark-field microscopy. The observed scattering peaks are suggested to result from plasmonic resonance of the gold nanopeas and nanorods in the Ga(2)O(3) nanowires. As the diameter of gold peapod increases, the resonance peak of the optical scattering spectra showed a red-shift. In addition, as the gold peas are elongated along one axis, the corresponding plasmon resonance peak splits into two peaks at shorter and longer wavelengths. The cladding Ga(2)O(3) dielectric layer also plays a key role in light-scattering behavior. The observed modulation in the p-polarized spectrum revealed that future vertical nanoplasmonic devices made by plasmonic nanocavity due to the short propagation length of surface plasmons can be realized and optimized.

Novel Semiautomated Method for Assessing in Vitro Cellular Antioxidant Activity Using the Light-Scattering Properties of Human Erythrocytes

The novel method developed for screening cellular antioxidant activity relies on differences in light-scattering properties (turbidity) between intact and lysed human erythrocytes. AAPH, a peroxyl radical generator, was used to enhance lipid peroxidation. The consequent hemolysis triggered a loss of the light-scattering ability in the lysed erythrocytes. When an antioxidant was added, the area under the absorbance decay curve (AUC) was linearly proportional to the concentration of antioxidant compound. This erythrocyte cellular antioxidant activity (ERYCA) method was found to be relatively fast, sensitive, accurate, and repeatable, even when using erythrocytes from different donors and for different storage times. The method was used to assess the antioxidant capacity of pure phenolic compounds, fruit juices, stimulant beverages, and blood plasma and compared with ORAC values. The values resulting from the two methods did not correlate as the mechanisms involved were different.

Layer-by-layer coating of bacteria with noble metal nanoparticles for surface-enhanced Raman scattering

A simple layer-by-layer method to coat the bacterial cells with gold and silver nanoparticles (AuNPs and AgNPs) for the acquisition of surface-enhanced Raman scattering (SERS) spectra is reported. First, the bacteria cell wall is coated with poly (allylamine hydrochloride) (PAH), a positively charged polymer, and then with citrate reduced Au or AgNPs. In order to increase the stability of the coating, another layer of PAH is prepared on the surface. The SEM and AFM images indicate that the nanoparticles are in the form of both isolated and aggregated nanoparticles on the bacterial wall. The coating of bacterial cells with AgNPs or AuNPs not only serves for their preparation for SERS measurement but also helps to visualize the coated of bacterial cells under the ordinary white-light microscope objective due to efficient light-scattering properties of Au and AgNPs. A comparative study single versus aggregates of bacterial cells is also demonstrated for possible single bacterial detection with SERS. The two bacteria that differ in shape and cell wall biochemical structure, Escherichia coli and Staphylococcus cohnii, Gram-negative and -positive, respectively, are used as models. The preliminary results reveal that the approach could be used for single bacterial cell identification.

Development of a light scattering solver applicable to particles of arbitrary shape on the basis of the surface-integral equations method of Müller type I Methodology, accuracy of calculation, and electromagnetic current on the particle surface

We develop a numerical algorithm for calculating the light-scattering properties of small particles of arbitrary shape on the basis of a method involving surface integral equations. The calculation error was estimated by performing a comparison between the proposed method and the exact Mie method with regard to the extinction efficiency factor, and the results show that the error is less than 1% when four or more nodes per wavelength are set on the surface of a spherical particle. The accuracy fluctuates in accordance with the distribution of nodal points on the particle surface with respect to the direction of propagation of the incident light. From our examinations, it is shown that the polar incidence alignment yields higher accuracy than equator incidence when a "latitude-longitude" type of mesh generation is adopted. The electric currents on the particle surface and the phase functions of all scattering directions are shown for particles shaped as spheres or hexagonal columns. It is shown that the phase function for a hexagonal column has four or eight cold spots. The phase function of a randomly oriented hexagonal column shows halolike peaks with size parameters of up to 20. This method can be applied to particles with a size parameter of up to about 20 without using the symmetry characteristic of the particle.

小惑星の光散乱特性--模擬室内実験から表面の組成と物理状態を探る (可視・近赤外域における大気〜地表面系放射伝達--その応用と利用 特集号)

小惑星の光散乱特性--模擬室内実験から表面の組成と物理状態を探る (可視・近赤外域における大気〜地表面系放射伝達--その応用と利用 特集号)

Self-Assembled Fibers Photopolymerized in Nematic Liquid Crystals: Stable Electrooptical Switching in Light-Scattering Mode

Liquid-crystalline (LC) gels showing stable light-scattering electrooptical properties have been prepared by the photopolymerization of a gelator forming self-assembled fibers in a room-temperature nematic liquid crystal. A polymerizable gelator having methacryloyl moieties self-assembles into finely dispersed fibers in the nematic liquid crystal, resulting in the formation of LC physical gels. Photopolymerization of the gelator in the gel states leads to the preparation of cross-linked fibrous networks. The LC polydomain structures effective for light-scattering electrooptical switching are kept after polymerization. The polymerized LC gels show stable reversible switching of electrooptical responses with enhanced threshold properties between 0 and 70 V.

Development of surface-textured hydrogenated ZnO:Al thin-films for μc-Si solar cells

This study addresses the optimization of rf magnetron-sputtered hydrogenated ZnO:Al (HAZO) films as front contacts in microcrystalline silicon solar cells. The front contact of a solar cell has to be highly conductive and highly transparent to visible and infrared radiation. Furthermore, it has to scatter the incident light efficiently in order for the light to be effectively trapped in the underlying silicon layers. In this research, HAZO films were rf-magnetron-sputtered on glass substrates from a ceramic (98 wt% ZnO, 2 wt% Al 2O 3) target. Various compositions of AZO films on glass substrates were prepared by changing the H 2/(Ar + H 2) ratio of the sputtering gas. The resulting smooth films exhibited high transparencies ( T ⩾ 85% for visible light including all reflection losses) and excellent electrical properties ( ρ = 2.7 × 10 −4 Ω · cm). Depending on their structural properties, these films developed different surface textures upon post-deposition etching using diluted hydrochloric acid. The light-scattering properties of these films could be controlled simply by varying the etching time. Moreover, the electrical properties of the films were not affected by the etching process. Therefore, within certain limits, it is possible to optimize the electro-optical and light-scattering properties separately. The microcrystalline silicon (μc-Si:H)-based p–i–n solar cells prepared using these new texture-etched AZO:H substrates showed high quantum efficiencies in the long wavelength range, thereby demonstrating effective light trapping. Using the optimum AZO:H thin-film textured surface, we achieved a p–i–n μc-Si solar cell efficiency of 7.78%.

Enhancing tissue-contrast imaging of the anterior eye

Optical coherence tomography (OCT) has become one of the most important diagnostic tools in ophthalmology. Originally used to examine the posterior eye, which includes the retina and optic nerve, it now is being applied to the anterior eye, which includes the cornea and iris.1, 2 The back of the eye has several tissue layers, each with different light-scattering properties. OCT uses these differences for image contrast that clearly distinguishes the posterior tissues. However, the scattering properties of anterior eye tissue layers are similar, so it is difficult to selectively obtain contrast with OCT. There are several ways to increase OCT exogenous contrast, such as using nanoparticles and dye molecules, but they are somewhat invasive and thus not convenient for daily clinical use. However, OCT endogenous contrasts may be useful. Doppler OCT provides selective contrast of vasculature.3 Spectroscopic OCT,4 based on tissue absorption, may also improve contrast. And polarization-sensitive OCT (PS-OCT)5 enables birefringence (double refraction), which is strongly associated with tissue composition. We are working on tissue-contrast OCT of the anterior eye using PS-OCT detection and signal processing. This method yields pseudo-color, tissue-contrast OCT images with various tissues displayed in different colors. It can be used to selectively contrast tissues of the anterior eye, including the cornea, conjunctiva, sclera, uvea, and trabecular meshwork. We used a swept-source PS-OCT system with a probe wavelength of 1.3μm. It enables 3D tomography based on standard scattering OCT and PS-OCT, which measures phase retardation.5 The depth resolution is 12μm and themeasurement speed is 20,000 depth scans/s. These specifications are superior to the corresponding quantities in ultrasound biomicroscopy, a standard modality for examining the front of the eye. Figure 1 Figure 1. Human anterior segment cross section using (a) scattering optical coherence tomography (OCT), and (b) polarization-sensitive OCT. These images were constructed from Interactive Science Publishing data sets (see Reference 6).

取向比对圆柱状冰晶粒子光散射特性的影响

取向比对圆柱状冰晶粒子光散射特性的影响

Wavelength-dependent backscattering measurements for quantitative real-time monitoring of apoptosis in living cells

Apoptosis--programmed cell death--is a cellular process exhibiting distinct biochemical and morphological changes. An understanding of the early morphological changes that a cell undergoes during apoptosis can provide the opportunity to monitor apoptosis in tissue, yielding diagnostic and prognostic information. There is avid interest regarding the involvement of apoptosis in cancer. The initial response of a tumor to successful cancer treatment is often massive apoptosis. Current apoptosis detection methods require cell culture disruption. Our aim is to develop a nondisruptive optical method to monitor apoptosis in living cells and tissues. This would allow for real-time evaluation of apoptotic progression of the same cell culture over time without alteration. Elastic scattering spectroscopy (ESS) is used to monitor changes in light-scattering properties of cells in vitro due to apoptotic morphology changes. We develop a simple instrument capable of wavelength-resolved ESS measurements from cell cultures in the backward direction. Using Mie theory, we also develop an algorithm that extracts the size distribution of scatterers in the sample. The instrument and algorithm are validated with microsphere suspensions. For cell studies, Chinese hamster ovary (CHO) cells are cultured to confluence on plates and are rendered apoptotic with staurosporine. Backscattering measurements are performed on pairs of treated and control samples at a sequence of times up to 6-h post-treatment. Initial results indicate that ESS is capable of discriminating between treated and control samples as early as 10- to 15-min post-treatment, much earlier than is sensed by standard assays for apoptosis. Extracted size distributions from treated and control samples show a decrease in Rayleigh and 150-nm scatterers, relative to control samples, with a corresponding increase in 200-nm particles. Work continues to correlate these size distributions with underlying morphology. To our knowledge, this is the first report of the use of backscattering spectral measurements to quantitatively monitor apoptosis in viable cell cultures in vitro.

Nanoshell-Enabled Photothermal Cancer Therapy: Impending Clinical Impact

Much of the current excitement surrounding nanoscience is directly connected to the promise of new nanoscale applications in cancer diagnostics and therapy. Because of their strongly resonant light-absorbing and light-scattering properties that depend on shape, noble metal nanoparticles provide a new and powerful tool for innovative light-based approaches. Nanoshellsspherical, dielectric core, gold shell nanoparticleshave been central to the development of photothermal cancer therapy and diagnostics for the past several years. By manipulating nanoparticle shape, researchers can tune the optical resonance of nanoshells to any wavelength of interest. At wavelengths just beyond the visible spectrum in the near-infrared, blood and tissue are maximally transmissive. When nanoshell resonances are tuned to this region of the spectrum, they become useful contrast agents in the diagnostic imaging of tumors. When illuminated, they can serve as nanoscale heat sources, photothermally inducing cell death and tumor remission. As nanoshell-based diagnostics and therapeutics move from laboratory studies to clinical trials, this Account examines the highly promising achievements of this approach in the context of the challenges of this complex disease. More broadly, these materials present a concrete example of a highly promising application of nanochemistry to a biomedical problem. We describe the properties of nanoshells that are relevant to their preparation and use in cancer diagnostics and therapy. Specific surface chemistries are necessary for passive uptake of nanoshells into tumors and for targeting specific cell types by bioconjugate strategies. We also describe the photothermal temperature increases that can be achieved in surrogate structures known as tissue phantoms and the accuracy of models of this effect using heat transport analysis. Nanoshell-based photothermal therapy in several animal models of human tumors have produced highly promising results, and we include nanoparticle dosage information, thermal response, and tumor outcomes for these experiments. Using immunonanoshells, infrared diagnostic imaging contrast enhancement and photothermal therapy have been integrated into a single procedure. Finally, we examine a novel "Trojan horse" strategy for nanoparticle delivery that overcomes the challenge of accessing and treating the hypoxic regions of tumors, where blood flow is minimal or nonexistent. The ability to survive hypoxia selects aggressive cells which are likely to be the source of recurrence and metastasis. Treatment of these regions has been incredibly difficult. Ultimately, we look beyond the current research and assess the next challenges as nanoshell-based photothermal cancer therapy is implemented in clinical practice.

Modeling of Light Scattering Properties of a Nanoshell on a Plane Interface: Influence of a Core Material and Polarization

Modeling of Light Scattering Properties of a Nanoshell on a Plane Interface: Influence of a Core Material and Polarization

Impact of Self-Assembly Properties on Antibacterial Activity of Short Acyl-Lysine Oligomers

We investigated both the structural and functional consequences of modifying the hydrophobic, lipopeptide-mimetic oligo-acyl-lysine (OAK) N(alpha)-hexadecanoyl-l-lysyl-l-lysyl-aminododecanoyl-l-lysyl-amide (c(16)KKc(12)K) to its unsaturated analog hexadecenoyl-KKc(12)K [c(16(omega7))KKc(12)K]. Despite similar tendencies for self-assembly in solution (critical aggregation concentrations, approximately 10 muM), the analogous OAKs displayed dissimilar antibacterial properties (e.g., bactericidal kinetics taking minutes versus hours). Diverse experimental evidence provided insight into these discrepancies: whereas c(16(omega7))KKc(12)K created wiry interconnected nanofiber networks, c(16)KKc(12)K formed both wider and stiffer fibers which displayed distinct binding properties to phospholipid membranes. Unsaturation also shifted their gel-to-liquid transition temperatures and altered their light-scattering properties, suggesting the disassembly of c(16(omega7))KKc(12)K in the presence of bacteria. Collectively, the data indicated that the higher efficiency in interfering with bacterial viability emanated from a wobbly packing imposed by a single double bond. This suggests that similar strategies might improve hydrophobic OAKs and related lipopeptide antibiotics.

Aggregate model of cometary dust: an application to comet Levy 1990XX

In the present work, the light-scattering properties of comet Levy 1990XX are studied through simulations using Ballistic Particle-Cluster Aggregation (BPCA) or Ballistic Cluster-Cluster Aggregation (BCCA) aggregates of up to 128 spherical monomers of different compositions (e.g. silicates, carbonaceous materials etc.) and the best-fitting theoretical polarization curve is generated using the SUPERPOSITION T-MATRIX code. The best-fitting refractive indices coming out from the present analysis show silicate behaviour when monomer radius is a m = 0.12 μm and provide excellent results on the maximum and negative degrees of linear polarization at a single wavelength λ = 0.485 μm for BCCA aggregates.