Analysis of integrated optofluidic lab-on-a-chip fluorescence biosensor based on transmittance of light through a fluidic gap

Sensitivity analysis is an important aspect to be looked into while designing lab-on-a-chip systems. In this paper we will be showing with appropriate design that the best sensitivity of the fluorescence biosensor is achieved for an optimal width of fluidic gap, corresponding to a particular mode spot size. We will be also showing that the sensitivity of the biosensor is affected by efficiency of light coupling, which is influenced by changes in the width of fluidic gap, refractive index of the fluid and higher order modes.

Diffuse optical tomographic imager using a single light source

Near-infrared diffuse optical tomography (DOT) technique has the capability of providing good quantitative reconstruction of tissue absorption and scattering properties with additional inputs such as input and output modulation depths and correction for the photon leakage. We have calculated the two-dimensional (2D) input modulation depth from three-dimensional (3D) diffusion to model the 2D diffusion of photons. The photon leakage when light traverses from phantom to the fiber tip is estimated using a solid angle model. The experiments are carried for single (5 and 6 mm) as well as multiple inhomogeneities (6 and 8 mm) with higher absorption coefficient in a homogeneous phantom. Diffusion equation for photon transport is solved using finite element method and Jacobian is modeled for reconstructing the optical parameters. We study the development and performance of DOT system using modulated single light source and multiple detectors. The dual source methods are reported to have better reconstruction capabilities to resolve and localize single as well as multiple inhomogeneities because of its superior noise rejection capability. However, an experimental setup with dual sources is much more difficult to implement because of adjustment of two out of phase identical light probes symmetrically on either side of the detector during scanning time. Our work shows that with a relatively simpler system with a single source, the results are better in terms of resolution and localization. The experiments are carried out with 5 and 6 mm inhomogeneities separately and 6 and 8 mm inhomogeneities both together with absorption coefficient almost three times as that of the background. The results show that our experimental single source system with additional inputs such as 2D input/output modulation depth and air fiber interface correction is capable of detecting 5 and 6 mm inhomogeneities separately and can identify the size difference of multiple inhomogeneities such as 6 and 8 mm. The localization error is zero. The recovered absorption coefficient is 93% of inhomogeneity that we have embedded in experimental phantom.

Electrochemical Integration of Graphene with Light-Absorbing Copper-Based Thin Films

We present an electrochemical route for the integration of graphene with light-sensitive copper-based alloys used in optoelectronic applications. Graphene grown using chemical vapor deposition (CVD) transferred to glass is found to be a robust substrate on which photoconductive CuxS films of 1-2 mu m thickness can be deposited. The effect of growth parameters on the morphology and photoconductivity of CuxS films is presented. Current-voltage (I-V) characterization and photoconductivity decay experiments are performed with graphene as one contact and silver epoxy as the other.

On the two dimensional effective electron mass in quantum wells, inversion layers and NIPI superlattices of Kane type semiconductors in the presence of strong light waves: Simplified theory and relative comparison

An attempt is made to study the two dimensional (2D) effective electron mass (EEM) in quantum wells (Qws), inversion layers (ILs) and NIPI superlattices of Kane type semiconductors in the presence of strong external photoexcitation on the basis of a newly formulated electron dispersion laws within the framework of k.p. formalism. It has been found, taking InAs and InSb as examples, that the EEM in Qws, ILs and superlattices increases with increasing concentration, light intensity and wavelength of the incident light waves, respectively and the numerical magnitudes in each case is band structure dependent. The EEM in ILs is quantum number dependent exhibiting quantum jumps for specified values of the surface electric field and in NIPI superlattices; the same is the function of Fermi energy and the subband index characterizing such 2D structures. The appearance of the humps of the respective curves is due to the redistribution of the electrons among the quantized energy levels when the quantum numbers corresponding to the highest occupied level changes from one fixed value to the others. Although the EEM varies in various manners with all the variables as evident from all the curves, the rates of variations totally depend on the specific dispersion relation of the particular 2D structure. Under certain limiting conditions, all the results as derived in this paper get transformed into well known formulas of the EEM and the electron statistics in the absence of external photo-excitation and thus confirming the compatibility test. The results of this paper find three applications in the field of microstructures. (C) 2011 Elsevier Ltd. All rights reserved.

Gallium and indium co-doped ZnO thin films for white light emitting diodes

Ga and In co-doped ZnO (GIZO) thin films together with ZnO, In-doped ZnO (IZO), Ga-doped ZnO (GZO), and IZO/GZO multilayer for comparison, were grown on corning glass and boron doped Si substrates by PLD. The photoluminescence spectra of GIZO showed a strong white light emission and the current-voltage characteristics showed relatively lower turn-on voltage and larger forward current. The CIE coordinates for GIZO were observed to be (0.31, 0.33) with a correlated colour temperature of 6650 K, indicating a cool white light, and establishing a possibility of white light emitting diodes. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Optical properties change in Sb40S40Se20 thin films by light-induced effect

Thin films of Sb40Se20S40 with thickness 1000 nm were prepared by thermal evaporation technique. The amorphous nature of the thin films was verified by X-ray diffractometer. The chemical composition of the deposited thin films was examined by energy dispersive X-ray analysis (EDAX). The changes in optical properties due to the influence of laser radiation on amorphous thin films of Sb40Se20S40 glassy alloy were calculated from absorbance spectra as a function of photon energy in the wavelength region 450-900 nm. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. It has been observed that laser-irradiation of the films leads to a decrease in optical band gap while increase in absorption coefficient. The decrease in the optical band gap is explained on the basis of change in nature of films due to disorderness. The optical changes are supported by X-ray photoelectron spectroscopy and Raman spectroscopy. (C) 2012 Elsevier B.V. All rights reserved.

Ferrocene-Conjugated Oxidovanadium(IV) Complexes as Potent Near-IR Light Photocytotoxic Agents

Ferrocene-conjugated oxidovanadium(IV) complexes [VO(Fc-tpy)(B)](ClO4)(2) (1-4) and [VO(Ph-tpy)(dppz)](ClO4)(2) (5) as a control [Fc = (eta(5)-C5H4)Fe-II(eta(5)-C5H5), Fc-tpy = 4'-ferrocenyl-2,2':6',2 `'-terpyridine, Ph-tpy = 4'-phenyl-2,2':6',2 `'-terpyridine, B = heterocyclic base: 2,2'-bipyridine (bpy in 1), 1,10-phenanthroline (phen in 2), dipyridoquinoxaline (dpq in 3), dipyridophenazine (dppz in 4)] were prepared and their DNA binding, DNA photocleavage activity and photocytotoxicity studied. The crystal structure of [VO(Fc-tpy)(bpy)](PF6)(2)center dot 3Me(2)CO shows a vanadyl group in six-coordinate (VON5)-O-IV coordination geometry, in which Fc-tpy and bpy display tridentate meridional and bidentate N-donor axial-equatorial binding modes, respectively. The one-electron paramagnetic complexes exhibit a charge-transfer band near 590 nm in DMF. The V-IV/V-III redox couple in 1-4 appears near -0.7 V, whereas the Fc moiety shows a response near 0.6 V vs. SCE in DMF/0.1 M TBAP. The complexes are good binders to calf thymus DNA with K-b values of 10(4)-10(6) M-1. DNA melting and viscometric data suggest groove and/or partial intercalative DNA binding of the complexes. Complexes 3-5 display DNA photocleavage activity in nearIR light of 785 nm. Complex 4 shows significant photocytotoxicity in visible light (400-700 nm) in HeLa cells with low dark toxicity.

Enhanced efficiency of tri-layered dye solar cells with hydrothermally synthesized titania nanotubes as light scattering outer layer

In the present study dye sensitized solar cells (DSSCs) have been fabricated with a tri-layer photo anode consisting of hydrothermally prepared titania nano tubes (TNT) having a diameter of 9-10 nm and length of several micrometers as outer layer, P25 TiO2 powder as transparent light absorbing middle layer and a compact TiO2 inner layer to improve the adhesion of different layers on a transparent conducting oxide coated substrate. In comparison to cells fabricated using TNTs or P25 alone, the tri-layer DSSCs exhibit an enhanced efficiency of 7.15% with a current density of 17.12 mA cm(-2) under AM 1.5 illumination. The enhancement is attributed to the light scattering generated by TNTs aggregates, reduction in electron transport resistance at the TiO2/dye/electrolyte interface and an improvement in electron life-time. (c) 2012 Elsevier B.V. All rights reserved.

Generalization of the collision cone approach for motion safety in 3-D environments

Avoidance of collision between moving objects in a 3-D environment is fundamental to the problem of planning safe trajectories in dynamic environments. This problem appears in several diverse fields including robotics, air vehicles, underwater vehicles and computer animation. Most of the existing literature on collision prediction assumes objects to be modelled as spheres. While the conservative spherical bounding box is valid in many cases, in many other cases, where objects operate in close proximity, a less conservative approach, that allows objects to be modelled using analytic surfaces that closely mimic the shape of the object, is more desirable. In this paper, a collision cone approach (previously developed only for objects moving on a plane) is used to determine collision between objects, moving in 3-D space, whose shapes can be modelled by general quadric surfaces. Exact collision conditions for such quadric surfaces are obtained and used to derive dynamic inversion based avoidance strategies.

Anomalous triple gauge boson couplings in e(-)e(+) -> gamma gamma for noncommutative standard model

We investigate e(+)e(-) -> gamma gamma process within the Seiberg-Witten expanded noncommutative standard model (NCSM) scenario in the presence of anomalous triple gauge boson couplings. This study is done with and without initial beam polarization and we restrict ourselves to leading order effects of noncommutativity i.e. O(Theta). The noncommutative (NC) corrections are sensitive to the electric component ((Theta) over bar (E)) of NC parameter. We include the effects of Earth's rotation in our analysis. This study is done by investigating the effects of noncommutativity on different time averaged cross section observables. We have also defined forward backward asymmetries which will be exclusively sensitive to anomalous couplings. We have looked into the sensitivity of these couplings at future experiments at the International Linear Collider (ILC). This analysis is done under realistic ILC conditions with the center of mass energy (cm.) root s = 800 GeV and integrated luminosity L = 500 fb(-1). The scale of noncommutativity is assumed to be Lambda = 1 TeV. The limits on anomalous couplings of the order 10(-1) from forward backward asymmetries while much stringent limits of the order 10(-2) from total cross section are obtained if no signal beyond SM is seen. (C) 2012 Elsevier B.V. All rights reserved.

Enhancement of circular differential deflection of light in an optically active medium

In this letter, we investigate the circular differential deflection of a light beam refracted at the interface of an optically active medium. We show that the difference between the angles of deviation of the two circularly polarized components of the transmitted beam is enhanced manyfold near total internal reflection, which suggests a simple way of increasing the limit of detection of chiro-optical measurements. (C) 2012 Optical Society of America

Synthesis and characterization of carbon-covered alumina (CCA) supported TiO2 nanocatalysts with enhanced visible light photodegradation of Rhodamine B

The anatase phase of titania (TiO2) nano-photocatalysts was prepared using a modified sol gel process and thereafter embedded on carbon-covered alumina supports. The carbon-covered alumina (CCA) supports were prepared via the adsorption of toluene 2,4-diisocyanate (TDI) on the surface of the alumina. TDI was used as the carbon source for the first time for the carbon-covered alumina support system. The adsorption of TDI on alumina is irreversible; hence, the resulting organic moiety can undergo pyrolysis at high temperatures resulting in the formation of a carbon coating on the surface of the alumina. The TiO2 catalysts were impregnated on the CCA supports. X-ray diffraction analysis indicated that the carbon deposited on the alumina was not crystalline and also showed the successful impregnation of TiO2 on the CCA supports. In the Raman spectra, it could be deduced that the carbon was rather a conjugated olefinic or polycyclic hydrocarbons which can be considered as molecular units of a graphitic plane. The Raman analysis of the catalysed CCAs showed the presence of both the anatase titania and D and G band associated with the carbon of the CCAs. The scanning electron microscope micrographs indicated that the alumina was coated by a carbon layer and the energy dispersive X-ray spectra showed the presence of Al, O and C in the CCA samples, with the addition of Ti for the catalyst impregnated supports. The Brunauer Emmet and Teller surface area analysis showed that the incorporating of carbon on the alumina surface resulted in an increase in surface area, while the impregnation with TiO2 resulted in a further increase in surface area. However, a decrease in the pore volume and diameter was observed. The photocatalytic activity of the nanocatalysts was studied for the degradation of Rhodamine B dye. The CCA-TiO2 nanocatalysts were found to be more photocatalytically active under both visible and UV light irradiation compared to the free TIO2 nanocatalysts.

Influence of anion on the quadratic nonlinearity and depolarization ratios of scattered second harmonic light from cation-pi complexes

We have investigated quadratic nonlinearity (beta(HRS)) and linear and circular depolarization ratios (D and D', respectively) of a series of 1:1 complexes of tropyliumtetrafluoroborate as a cation and methyl-substituted benzenes as pi-donors by making polarization resolved hyper-Rayleigh scattering measurements in solution. The measured D and D' values are much lower than the values expected from a typical sandwich or a T-shaped geometry of a complex. In the cation-pi complexes studied here, the D value varies from 1.36 to 1.46 and D' from 1.62 to 1.72 depending on the number of methyl substitutions on the benzene ring. In order to probe it further, beta, D and D' were computed using the Zerner intermediate neglect of differential overlap-correction vector self-consistent reaction field technique including single and double configuration interactions in the absence and presence of BF4- anion. In the absence of the anion, the calculated value of D varies from 4.20 to 4.60 and that of D' from 2.45 to 2.72 which disagree with experimental values. However, by arranging three cation-pi BF4- complexes in a trigonal symmetry, the computed values are brought to agreement with experiments. When such an arrangement was not considered, the calculated beta values were lower than the experimental values by more than a factor of two. This unprecedented influence of the otherwise ``unimportant'' anion in solution on the beta value and depolarization ratios of these cation-pi complexes is highlighted and emphasized in this paper. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4716020]