Investigation on Optical Properties of Ag–Au Alloy Nanoparticles

The outstanding chemical stability of Au and intense localized surface plasmon resonance of Ag make it possible to obtain a nanostructure with a good balance of good chemical stability and optical response. In this paper, we investigated the relationship between optical properties and the composition and size of Ag–Au alloy nanoparticle with numerical calculation by applying experimental data. Simplified empirical formulas are proposed through numerical simulation. The properties of extinction efficiency and the relative contribution of scattering and absorption efficiency to the extinction efficiency have been researched in detail. The calculated result and experimental data has been compared, and good agreement is obtained. Our work contributes greatly to catalysis application of Au–Ag alloy NPs in specific regions.     

Phase Transition and Optical Properties of DNA–Gold Nanoparticle Assemblies

We review recent work on DNA-linked gold nanoparticle assemblies. The synthesis, properties, and phase behavior of such DNA–gold nanoparticle assemblies are described. These nanoparticle assemblies have strong optical extinction in the ultraviolet and visible light regions; hence, the technique is used to study the kinetics and phase transitions of DNA–gold nanoparticle assemblies. The melting transition of DNA–gold nanoparticle assemblies shows unusual trends compared to those of free DNA. The phase transitions are influenced by many parameters, such as nanoparticle size, DNA sequence, DNA grafting density, DNA linker length, interparticle distance, base pairing defects, and disorders. The physics of the DNA–gold nanoparticle assemblies can be understood in terms of the phase behavior of complex fluids, with the colloidal gold interaction potential dominated by DNA hybridization energies.     

Simulation of the Nonlinear Optical Properties of Colloids Containing Metallic Core–Dielectric Shell Nanoparticles

Nonlinear (NL) optical properties of composite materials containing metallic core–dielectric shell nanoparticles in aqueous solution were investigated numerically using the Maxwell–Garnett model and the degenerate electron gas model. Influence of geometry and excitation laser intensity was considered to describe the local field factor and the third-order NL susceptibility.     

Simulation of the Linear and Nonlinear Optical Properties of Colloids Containing Metallic Core–Dielectric Shell Nanoellipsoids

Linear and nonlinear (NL) optical properties of colloids containing metallic core–dielectric shell nanoellipsoids (NEs) were studied using the Maxwell-Garnett model. Influence of the NE geometry and the linear refraction index of the shell and the host on the linear optical properties and the enhancement factor due to the local field factor of metallic NEs in aqueous solution were analyzed. The expression for the third-order NL susceptibility for this composite material was obtained based on the NL response of aligned NEs. Results show that the plasmon resonance peak (PRP) and the enhancement factors can be tuned changing the NE geometry and the dielectric properties of the shell and the host.     

Structural,Morphological, and Optical Properties of Nanocrystalline (Bi2O3)1−x:(TiO2)x Thin Films for Transparent Electronics

The fabrication of low cost and eco-friendly transparent electronics using metal oxide semiconductors is still a challenging task. In this work, transparent nanocrystalline (Bi₂O₃)_1−x:(TiO₂)_x thin films were synthesized using a pulsed laser deposition technique (PLD); XRD analysis shows the films have polycrystalline structure of monoclinic Bi₂O₃; morphological and topographical properties were analyzed by SEM and AFM showing the films have smooth surfaces with RMS roughness (4.26–7.37 nm) with micro-and nano-spheres (2 μm to 23 nm); the optical properties were analyzed by Uv-Vis spectrometer and revealed high transmittance in the visible range; the best results were obtained at x = 0.05 where the highest crystallinity, highest transmittance (> 82%), and highest band gap (3.769 eV) were achieved; and empirical models have been proposed to estimate the band gap and Bi–O bond lengths as a function of TiO₂ concentration with excellent coincidence with the experimental data.

     

Frequency-Dependent Polarization Properties of Local Electric Field in Gold–Dielectric Multi-Nanoshells

The polarization properties of the local electric field in the gold–dielectric–gold multilayer nanoshells are investigated by theoretical calculation based on the quasi-static approximation. The calculation results show that the complete polarized incident light does not only stimulate the same directional polarized local electric field. The polarized angle of the local field may changes from 0° to 90° as the wavelength and location are changed. The distributions of local field polarization are different in dielectric layer or gold shell and display different features in different plasmonic hybridization mode. As the incident wavelength is increased, the hot spot of polarizing angle moves monotonously in the middle dielectric shell, whereas moves nonmonotonously in the gold shell and surrounding environment. In the gold shell, the gap between hot spots of polarizing angle may occur at the resonance frequency. However, the hot spots of polarizing angle always occur at the resonance frequencies in the surrounding environment. These interesting results show that the single-molecule detection based on metal nanostructure induced surface-enhanced Raman scattering and surface enhanced fluorescence could be optimized by adjusting the incident light polarization and frequency.     

Measurement of THz Spot Sizes with a λ/200 Diameter in the Near-Field of a Metal Tip

We report on a method to obtain asub-wavelength resolution in terahertz time-domain imaging. In our method,a sharp copper tip is used to locallydistort and concentrate the THz electricfield. The distorted electric field, presentmainly in the near field of the tip, iselectro-optically measured in an (100)oriented GaP crystal. By raster scanning the tipalong the surface of the crystal we find asmallest THz spot size of 10 m forfrequencies from 0.1 to 2.5 THz. For ourpeak frequency of 0.15 THz this corresponds to aresolution of /200. Our setup has thepotential to reach a resolution down to afew m, and is a promising candidate tostudy single, living cells in the THzfrequency range.     

Dissolved Organic Matter Characteristics Across a Subtropical Wetland’s Landscape: Application of Optical Properties in the Assessment of Environmental Dynamics

Wetlands are known to be important sources of dissolved organic matter (DOM) to rivers and coastal environments. However, the environmental dynamics of DOM within wetlands have not been well documented on large spatial scales. To better assess DOM dynamics within large wetlands, we determined high resolution spatial distributions of dissolved organic carbon (DOC) concentrations and DOM quality by excitation–emission matrix spectroscopy combined with parallel factor analysis (EEM–PARAFAC) in a subtropical freshwater wetland, the Everglades, Florida, USA. DOC concentrations decreased from north to south along the general water flow path and were linearly correlated with chloride concentration, a tracer of water derived from the Everglades Agricultural Area (EAA), suggesting that agricultural activities are directly or indirectly a major source of DOM in the Everglades. The optical properties of DOM, however, also changed successively along the water flow path from high molecular weight, peat-soil and highly oxidized agricultural soil-derived DOM to the north, to lower molecular weight, biologically produced DOM to the south. These results suggest that even though DOC concentration seems to be distributed conservatively, DOM sources and diagenetic processing can be dynamic throughout wetland landscapes. As such, EEM–PARAFAC clearly revealed that humic-enriched DOM from the EAA is gradually replaced by microbial- and plant-derived DOM along the general water flow path, while additional humic-like contributions are added from marsh soils. Results presented here indicate that both hydrology and primary productivity are important drivers controlling DOM dynamics in large wetlands. The biogeochemical processes controlling the DOM composition are complex and merit further investigation.     

Near-infrared Plasmonic Far-field Nanofocusing Effects with Elongated Depth of Focus based on Hybrid Au–Dielectric–Ag Subwavelength Structures

In this paper, we propose a new far-field nanofocusing lens with elongated depth of focus (DOF) under near-infrared (NIR) wavelength. The surface plasmons can be excited by using the hybrid metal–insulator–metal (MIM) subwavelength structure under the NIR wavelength. The constructive interference of surface plasmons launched by the subwavelength MIM structure can form a nanoscale focus that is modulated by the novel metal grating from the near field to the far field. The numerical simulations demonstrated that a nanoscale focal spot (in plane focal area 0.177λ ²) with elongated DOF (3.358λ) and long focal length (5.084λ) can be realized with reasonably designing parameters of the lens. By controlling the positions of the inner radii of each slit ring and the grating width, the focal length, focal spot, and DOF can be tuned easily. This design method, which can obtain the nanoscale focal spot and micron DOF in far field under NIR illumination, paved the road for utilizing the NIR plasmonic lens in superresolution optical microscopic imaging, optical trapping, biosensing, and complex wavefront/beam shaper.     

Dielectric Properties Based Detection of Heavy Metal Contaminated Soil in the Frequency Range from 10 MHz to 1 GHz

Physical parameters based electromagnetic methods are promising technologies to detect contaminated sites. In these methods, the dielectric property is a key parameter. In this paper, we studied the dielectric characteristics of heavy metal contaminated soil. The chromium contaminated soil was made into samples, and the open-ended coaxial line was adopted as the measurement method. Experiments were conducted in the frequency band between 10 MHz and 1 GHz. The results showed that the complex permittivity, including the real part and the imaginary part, changes as the ionic content changes. Especially, at low frequencies (<50 MHz), the complex permittivity increases significantly with the increase of ionic content. In addition, it also could be seen that the water content of the soil also affects the complex permittivity. We proposed to adopt the drying method or the Time Domain Reflection method to determine the water content. The dielectric parameters are most affected by the ionic content after knowing the water content. Therefore, it is feasible to detect heavy metal contaminated sites based on dielectric properties.     

Dynamics of plasma−dust structures formed in a trap created in the narrowing of a current channel in a magnetic field

The geometry and dynamics of plasma?dust structures in a longitudinal magnetic field is studied experimentally. The structures are formed in a glow-discharge trap created in the double electric layer produced as a result of discharge narrowing by means of a dielectric insert introduced in the discharge tube. Studies of structures formed in the new type of glow-discharge trap are of interest from the standpoint of future experiments with complex plasmas in superstrong magnetic fields in which the dust component is magnetized. Different types of dielectric inserts were used: conical and plane ones with symmetric and asymmetric apertures. Conditions for the existence of stable dust structures are determined for dust grains of different density and different dispersity. According to the experimental results, the angular velocity of dust rotation is ≥10 s^–1, which is the fastest type of dust motion for all types of discharges in a magnetic field. The rotation is interpreted by analyzing the dynamics of individual dust grains.     

Properties of the permeability transition in VDAC1−/− mitochondria

Opening of the permeability transition pore (PTP), a high-conductance mitochondrial channel, causes mitochondrial dysfunction with Ca²⁺ deregulation, ATP depletion, release of pyridine nucleotides and of mitochondrial apoptogenic proteins. Despite major efforts, the molecular nature of the PTP remains elusive. A compound library screening led to the identification of a novel high affinity PTP inhibitor (Ro 68-3400), which labeled a ∼32 kDa protein that was identified as isoform 1 of the voltage-dependent anion channel (VDAC1) [A.M. Cesura, E. Pinard, R. Schubenel, V. Goetschy, A. Friedlein, H. Langen, P. Polcic, M.A. Forte, P. Bernardi, J.A. Kemp, The voltage-dependent anion channel is the target for a new class of inhibitors of the mitochondrial permeability transition pore. J. Biol. Chem. 278 (2003) 49812–49818]. In order to assess the role of VDAC1 in PTP formation and activity, we have studied the properties of mitochondria from VDAC1^−/− mice. The basic properties of the PTP in VDAC1^−/− mitochondria were indistinguishable from those of strain-matched mitochondria from wild-type CD1 mice, including inhibition by Ro 68-3400, which labeled identical proteins of 32 kDa in both wild-type and VDAC1^−/− mitochondria. The labeled protein could be separated from all VDAC isoforms. While these results do not allow to exclude that VDAC is part of the PTP, they suggest that VDAC is not the target for PTP inhibition by Ro 68-3400.     

Plasmon Interpretation of 25 cm−1 Mode in DNA

Abstract

An extension of the effective field approach for the normal mode dynamics of dissolved DNA polymers has been applied to study the vibrational modes of DNA-hydration sheath-counterion system, to include the effect of site bound counterions on the system dynamics. An alternative interpretation has been suggested for a 25 cm^?1 mode recently observed in DNA samples and interpreted earlier as an interhelical mode. Analysing the eigenvectors this mode is found to possess a large electric dipole moment with longitudinal collective oscillations of the system. These characteristics identify this mode as a collective plasmon mode. Possible physical reasons for the existence of this character have been presented.     

Spatial Variability of Soil Chemical Properties of a Prairie–Forest Transition in Louisiana

Woody plant expansion, particularly eastern red cedar (Juniperus virginiana L.), has been a major threat to Louisiana calcareous prairies. Previous studies have shown that woody plant expansion into grasslands is associated with an increase in soil heterogeneity. We studied the within site spatial variability and among site differences of surface (0–15 cm depth) soil pH, electrical conductivity (EC), and Mehlich III extractable Ca, Mg, K, Fe and Mn from three remnant prairie-forest associations in Winn Parish, Louisiana. The prairie soil was consistently basic (pH > 7.0) and the forest soil was acidic (pH < 7.0) while the transition soil was neutral (pH = 7.0). A nonparametric statistical test for the equality of medians among sites showed the median values of the soil attributes differed (α = 0.05) except for soil Ca and Fe. The similarity in Ca concentration among sites was attributed to the calcareous parent material common to the three sites. Geostatistical analysis showed that spatial dependence was expressed over a range of 20–30 m for most of the soil attributes considered. Semivariogram shapes were similar among sites, suggesting the greater control of soil parent material on the observed spatial soil pattern. Shorter range of variation emerged only for soil pH when soil data from the forest and transition were deleted, indicating the scaling characteristics of soil pH and its susceptibility to plant induced changes. It is concluded that soil pH can be used as an index to determine prairie-forest boundary, and to access the impact of eastern red cedar on these and similar sites derived from calcareous parent material. Further, results from this study can be used for designing future ecological studies within the prairie by taking the soil spatial variability into account.     

Photosynthetic Properties of Photosystem Ⅱ in Arabidopsis thaliana Ipa1 Mutant

In a previous study, we characterized a high chlorophyll fluorescence Ipal mutant of Arabidopsis thallana, in which approximately 20% photosystem （PS） Ⅱ protein is accumulated. In the present study, analysis of fluorescence decay kinetics and thermoluminescence profiles demonstrated that the electron transfer reaction on either the donor or acceptor side of PSII remained largely unaffected in the Ipa1 mutant. In the mutant, maximal photochemical efficiency （Fv/Fm, where Fm is the maximum fluorescence yield and Fv is variable fluorescence） decreased with increasing light intensity and remained almost unchanged in wildtype plants under different light conditions. The Fv/Fm values also increased when mutant plants were transferred from standard growth light to low light conditions. Analysis of PSll protein accumulation further confirmed that the amount of PSll reaction center protein is correlated with changes in Fv/Fm in Ipal plants. Thus, the assembled PSll in the mutant was functional and also showed increased photosensitivity compared with wild-type plants.     

Influence of Matrix Metalloproteinase-1 Gene −1607 (1G/2G) (rs1799750) Promoter Polymorphism on Circulating Levels of MMP-1 in Chronic Pancreatitis

This study investigated the role of ?1607 (1G/2G) (rs1799750) polymorphism of the MMP-1 gene in chronic pancreatitis. We genotyped 100 patients with chronic pancreatitis and 100 control subjects using tetra-primer ARMS-PCR followed by agarose gel electrophoresis. Serum levels of MMP-1 were determined by Elisa. Statistical analysis was applied to test the significance of the results. The genotypic and allelic distribution varied significantly between the disease group and the control subjects [OD = 1.981 (1.236–3.181), p = 0.004]. MMP-1 levels were higher in subjects homozygous for the 2G allele than in subjects with the 1G allele. The present study revealed a significant association of the MMP-1 ?1607 1G/2G (rs1799750) gene promoter polymorphism with chronic pancreatitis, and it can be considered a biological marker in the etiology of chronic pancreatitis.     

Glycoengineering of Interferon-β 1a Improves Its Biophysical and Pharmacokinetic Properties

The purpose of this study was to develop a biobetter version of recombinant human interferon-β 1a (rhIFN-β 1a) to improve its biophysical properties, such as aggregation, production and stability, and pharmacokinetic properties without jeopardizing its activity. To achieve this, we introduced additional glycosylation into rhIFN-β 1a via site-directed mutagenesis. Glycoengineering of rhIFN-β 1a resulted in a new molecular entity, termed R27T, which was defined as a rhIFN-β mutein with two N-glycosylation sites at 80^th (original site) and at an additional 25^th amino acid due to a mutation of Thr for Arg at position 27^th of rhIFN-β 1a. Glycoengineering had no effect on rhIFN-β ligand-receptor binding, as no loss of specific activity was observed. R27T showed improved stability and had a reduced propensity for aggregation and an increased half-life. Therefore, hyperglycosylated rhIFN-β could be a biobetter version of rhIFN-β 1a with a potential for use as a drug against multiple sclerosis.     

Properties of a Δ5-fatty acyl-CoA desaturase in the cotyledons of developing Limnanthes alba

A Δ5-fatty acid desaturase activity in extracts of developing meadowfoam (Limnanthes alba) seeds was characterized. Since the system was unstable after fractional centrifugation, only the cell-free homogenate was employed in these studies. Maximal enzyme activity was observed at pH 8. A time-course analysis of the substrates and products of the reaction suggested that the Δ5 desaturation occurs on an acyl-CoA. The desaturase activity was stimulated by n-octyl-glucopyranoside, catalase, ferredoxin, and several other compounds. Inhibition was observed with Triton X-100, p-chloromercuribenzoate, dithiothreitol, cysteine, and several other compounds. The enzyme was not inhibited by carbon monoxide (95%) suggesting that it is not associated with cytochrome P-450. Eicosanoyl-CoA saturated the enzyme at 1.5 μm and was inhibitory at higher concentrations. The desaturase had an apparent K_m of 23 μm for O₂. NADH was a better electron donor than NADPH. Among the potential substrates tested, the enzyme preferred eicosanoyl-CoA, but also desaturated palmitoyl-CoA, stearoyl-CoA, and eicosanoyl-ACP at fairly high rates.