Test of a model of stress-dependent diffusion by means of combined colored tracer and birefringence profile measurements

In the present paper we further test a model of stress-dependent diffusion previously used with success to simulate the variation from Case I to Case II penetration kinetics in the system liquid methylene chloride-uniaxially oriented cellulose acetate film, according to whether penetration occurs across or along the axis of preferred macromolecular orientation. Data on penetration rates, optical density profiles (using a colored tracer), and the corresponding birefringence profiles, characteristics of these penetration modes in the aforesaid system, are presented and compared with appropriate model uptake kinetic curves and penetrant concentration and compressive differential swelling stress profiles. It is shown that the salient features of the observed experimental behavior are in general accord with model predictions based on physically realistic assumptions.     

Controlling Spatial Heat and Light Distribution by Using Photothermal Enhancing Auto‐Regulated Liposomes (PEARLs)

Photothermal therapy (PTT) is enhanced by the use of nanoparticles with a large optical absorption at the treatment wavelength. However, this comes at the cost of higher light attenuation that results in reduced depth of heating as well as larger thermal gradients, leading to potential over‐ and under‐treatment in the target tissue. These limitations can be overcome by using photothermal enhancing auto‐regulating liposomes (PEARLs), based on thermochromic J‐aggregate forming dye–lipid conjugates that reversibly alter their absorption above a predefined lipid phase‐transition temperature. Under irradiation by near‐infrared light, deeper layers of the target tissue revert to the intrinsic optical absorption, halting the temperature rise and enabling greater light penetration and heat generation at depth. This effect is demonstrated in both nanoparticle solutions and in gel phantoms containing the nanoparticles.     

Optical excitations in carbon nanoscrolls

The optical properties of carbon nanoscrolls in the presence of uniform electric fields are investigated by using gradient approximation. Absorption spectra exhibit rich prominent peaks structures, which is caused by one-dimensional sub-bands. The numbers, spectral intensities, and energies of the absorption peaks are strongly dependent on the geometry and the electric field strength. There exists an optical selection rule originating from the two equivalent sublattices in graphene. The two-fold degeneracy of the absorption peaks can be lifted by the inter-wall interactions or the electric field. The variations of the absorption peak energies with the geometry and field strength are also explored. These theoretical predictions can be validated by optical absorption measurements.     

Pulsed Photoacoustic Study of the Diffusion of Chromophores in Human Skin

The technique of pulsed photoacoustic spectroscopy was used to investigate the diffusion of chromophores in human skin. The kinetic of diffusion has been studied for five solutions at different concentrations in a mixture of chromophores, as used in commercial sunscreens. In addition to the classical macroscopic interpretation of the diffusion process, a new method is shown to give more detailed information on chromophore presence at different depths in skin. For the first time, results are expressed in the frequency domain by means of the Fourier transform applied to the photoacoustic signal. The spectra are discussed versus the depth in skin samples and the time of diffusion kinetics. This new method of data analysis is shown to be very useful for understanding the influence of the internal structure of a medium on the penetration rate of chromophores into skin.     

Soret effect of nonionic surfactants in water studied by different transient grating setups

We studied the thermal diffusion behavior of the nonionic surfactant solutions C 12E 6/water and C 12E 5/water at different concentrations and temperatures using thermal diffusion forced Rayleigh scattering (TDFRS). Two different types of TDFRS setups have been applied. In the classical TDFRS, we use an argon laser to write the optical grating into the sample by using a small amount of ionic dye to convert the optical grating into a temperature grating. In the other setup, called IR-TDFRS, we use an infrared laser as the writing beam, which utilizes the water absorption band to convert the optical grating into a temperature grating. The measurements by IR-TDFRS show a one-mode signal for all concentrations and temperatures, while the signal in the classical TDFRS consists of two modes for higher temperatures and lower surfactant concentrations (Ning, H.; et al. J. Phys. Chem. B 2006, 110, 10746). We find good agreement between the Soret coefficient determined in the IR-TDFRS and the one derived from the first fast mode in the previous studies. The Soret coefficient of the nonionic solutions is positive and enhanced at the critical point. In general, the Soret coefficient of the micelles tends to increase with temperature. We found that the presence of the second mode observed in the classical TDFRS is related to the addition of the ionic dye, but even with the ionic dye it is not possible to observe a second mode in the IR-TDFRS. The origin of the second mode is discussed in terms of charged micelles and an inhomogenous dye distribution in the temperature gradient.     

Characterizing ablation and aerosol generation during elemental fractionation on absorption modified lithium tetraborate glasses using LA-ICP-MS

The influence of sample matrix composition, absorption behavior and laser aerosol particle size distribution on elemental fractionation in laser ablation inductively coupled plasma mass spectrometry was studied for nanosecond laser ablation at a wavelength of 266 nm. To this end, lithium tetraborate glass samples with different iron oxide contents and trace amounts of a group of 11 elements were prepared synthetically. The samples were characterized in terms of optical absorbance, melting points, trace element concentrations and homogeneity. UV/VIS spectra showed that sample absorption rises with increasing Fe₂O₃ content. Crater depths and time-dependent particle size distributions were measured, and ablated and transported sample volumes were estimated. Furthermore, the laser aerosol was filtered using a particle separation device and transient ICP-MS signals were acquired with and without filtering the aerosol. The results demonstrate that the amount of ablated sample is related to the absorption coefficient of the sample and therefore to the optical penetration depth of the laser beam into the sample. The higher energy densities resulting from the shorter penetration depths result in smaller average particle sizes for highly absorbing samples, which allows more efficient transport to and atomization and excitation of the ablated material within the ICP. The particle size distribution changes continuously with ablation time, and larger particle fractions occur mainly at the beginning of the ablation, which leads to particle-related fractionation processes at the beginning of the transient signal. Exceeding a critical depth to diameter ratio, laser-related elemental fractionation processes occur. Changes in the volatile to non-volatile element intensity ratio after the aerosol is filtered indicate that particle size-related enrichment processes contribute to elemental fractionation.     

Measurement of the penetration depths of red and near infrared light in human "ex vivo" tissues

The increasing application of light in new medical treatments has led to the need for optical characterization of tissues in order to obtain correct dosimetry. This study presents the results of measurements of the optical penetration depth of different human tissues based on the diffusion approximation of the transport theory of light.     

In‐depth diffusion of oxygen into LDPE exposed to an Ar–O2 atmospheric post‐discharge: a complementary approach between AR‐XPS and Tof‐SIMS techniques

The in‐depth oxygen diffusion into a low density polyethylene film is performed in the post‐discharge of an atmospheric plasma torch, supplied in argon as carrier gas and with or without oxygen as reactive gas. The chemical and structural properties of the polymer surface and bulk are studied in terms of plasma parameters (treatment time, power, and reactive gas flow rate). A good correlation between XPS and Fourier transform infrared spectroscopy analyses is demonstrated. The penetration depth of oxygen into the bulk of the polymer is investigated by angle resolved‐XPS and time‐of‐flight SIMS. It is shown that, depending on the plasma conditions, oxygen could penetrate up to 20–40 nm into the low density polyethylene during the atmospheric plasma treatment. Copyright © 2014 John Wiley & Sons, Ltd.     

染料影像的遮盖效率与吸光特性

本工作测定了油溶性内偶成色剂形成的染料影像的遮盖效率和吸收光谱,并研究了染料影像的遮盖效率和密度之间的关系,发现遮盖效率随密度的增大而减小,吸收谱带随密度的增大而变宽。这些结果同Gledhill和Julian的理论是相符的。实验结果表明,成色剂的分散度对染料影像的吸收谱带有一些影响,而对遮盖效率几乎没有影响。     

Applicability of shrinking core model on the adsorption of heavy metals by clarified sludge from aqueous solution

Shrinking Core model, widely accepted in the solid-fluid non-catalytic reaction system was applied to analyze the adsorption of metal ions like Zn(II), Cr(VI), Cd(II) and Pb(II) from the aqueous solutions onto the clarified sludge (CLS). The diffusivities of different metal ions in clarified sludge were determined by global optimization. The depth of penetration was also estimated for different initial concentrations. The experimental concentration profiles at various initial concentrations for all these four different metal ions matched well with the model predictions.     

THE MEASUREMENT OF DIHEMATOPORPHYRIN ETHER CONCENTRATION IN TISSUE BY REFLECTANCE SPECTROPHOTOMETRY

The in vivo quantitation of local photosensitizer concentration is an important problem in photodynamic therapy because tumor response depends on this parameter. This paper describes a new method for measuring dihematoporphyrin ether (DHE) concentration by reflectance spectrophotometry—a technique which could be applied to other photosensitizers. The absorbance due to the 630 nm absorption peak of DHE was determined by obtaining diffuse reflectance spectra before and after the addition of DHE in the form of Photofrin II. Spectra were obtained by placing an optical fiber bundle source and single fiber detectors in contact with the tissue surface. The sensitivity of the technique was measured for three tissues in vitro with a range of optical properties as well as for Nutralipid—a liquid with a very high scattering to absorption ratio. The results were in qualitative agreement with the predictions of a diffusion model of light propagation although a systematic discrepancy was observed. The technique was also successfully demonstrated in vivo for VX-2 carcinomas implanted in rabbit ears by correlating simultaneous absorbance measurements with gamma counting of radiolabeled ^6-4Cu Photofrin II. Our results suggest that reflectance spectrophotometry may be a useful clinical and research tool for the in vivo quantitation of DHE and other photosensitizers.     

Spectral characteristics and nonlinear studies of crystal violet dye

Solid-state dye-doped polymer is an attractive alternative to the conventional liquid dye solution. In this paper, the spectral characteristics and the nonlinear optical properties of the dye crystal violet are studied. The spectral characteristics of crystal violet dye doped poly(methylmethacrylate) modified with additive n-butyl acetate (nBA) are studied by recording its absorption and fluorescence spectra and the results are compared with the corresponding liquid mixture. The nonlinear refractive index of the dye in nBA and dye doped polymer film were measured using z-scan technique, by exciting with He-Ne laser. The results obtained are intercompared. Both the samples of dye crystal violet show a negative nonlinear refractive index. The origin of optical nonlinearity in the dye may be attributed due to laser-heating induced nonlinear effect.     

Fiber-optic fluorometer signal enhancement and application to biosensor design

Fiber-optic fluorescence spectroscopy is currently the focus of active research because of the high sensitivity of fluorimetry and capacity for remote analysis with optical fibers. It is shown here that a further increase in sensitivity can be achieved by placing a mirror within a few fiber diameters of the distal end of the optical fiber in a solution of flourophore. A potentially four-fold signal enhancement results which is due to an increase in the excitation intensity as well as the reflection of the collected emitted light. The enhancement is shown to be dependent on the pathlength and concentration of the fluorophore, as well as the numerical aperture and core diameter of the optical fiber. The limit of detection of the fluorometer, which incorporates a mirror, is nanomolar dye concentrations, with the maximum response in path lengths of dye that are in the order of 6 fiber diameters. This principle can be applied to the design of optical sensors for continuously monitoring the concentration of specific biochemicals, and a conceptual design for such a sensor is described. A mathematical model is presented which describes the fluorescence output signal of a fiber-optic flourometer which incorporates a mirror.     

EXCITATION ENERGY TRANSFER IN BILIRUBIN-CHLOROPHYLL AGGREGATES

Abstract— Solutions of chlorophyll a (chl a ) with different concentrations of bilirubin (blr) were used as a model system for studying the mechanism of energy transfer between bili-proteins and chl in blue-green algae. Several optical properties such as the absorption spectra, emission spectra for different wavelengths of excitation, degree of polarization and lifetime of fluorescence were measured. The measurements were carried out in several solvents (of different hydrogen bond-forming capacities) and at various dye concentrations.
The results indicate that aggregates of chl with blr are formed. Energy absorbed by blr in the aggregates is emitted as chlorophyll fluorescence, indicating energy transfer from blr to chl within the aggregate. The fluorescence yield and fluorescence polarization of aggregates are lower than those of isolated chl.     

Microbubbles and Nanodrops for photoacoustic tomography

Photoacoustic imaging holds a unique position in medical imaging technology by interlinking optical and acoustic techniques. Photoacoustic methods have shown potential for real-time, noninvasive imaging of structural and functional properties of biological tissues and organs based on optical transmission and acoustic reception, but with limited penetration depth and specificity due to strong light scattering and absorption in tissues and overlapping absorption spectra of various endogenous absorbers. Incorporation of tailor-made microbubbles and nanodrops comprising light-absorbing molecules or nanoparticles shows the potential to overcome such detection limitations. Microbubbles may be driven into powerful radial oscillations, thereby amplifying the acoustic emission and focusing it to the bubble's resonant frequency. Nanodrops may be vaporized into microbubbles, further amplifying the thermoelastic response. This review surveys advancements of this emerging imaging technology over the past decade.     

Sol-Gel Derived Thin Films for Hydrogen Sulphide Gas Sensing

Utilizing the sol-gel fabrication route, we have successfully modified and tailored the optical absorption in the visible spectrum of thionine dye trapped in an MTMS gel-matrix to coincide with the emission of a red diode laser operating at 660 nm. These thionine-doped MTMS thin films coated onto transparent substrates have shown a remarkable change in optical absorption in the presence of gaseous hydrogen sulphide (H₂S) diluted in air and in the absence of any buffer gas. The rapid response, sensitivity, reversibility and durability shown by this material can be exploited in developing absorption-based optical H₂S sensors in either an integrated optics or all-optical fiber approach using a red diode laser source.     

Elliptical diffusion of dye in hexagonal columnar polycatenar mesophases

We have studied polycatenar compounds which exhibit hexagonal columnar mesophases. In the planar orientation of these mesophases, the elliptical diffusion of the dissolved dyes is visualized by taking several pictures of the sample. The diffusion ratio D// /D is deduced for these columnar mesophases. Furthermore, using a classical optical absorption technique, we present measurements of dye diffusion in the same mesophases. The diffusion constants are measured in two geometries, along and perpendicular to the columns. The diffusion anisotropy ratios are in agreement with those deduced from the ellipse axes. The structure of these new columnar mesophases exhibited by rod-like mesogens is compared with that of disk-like mesogens.     

Elliptical diffusion of dye in hexagonal columnar polycatenar mesophases

We have studied polycatenar compounds which exhibit hexagonal columnar mesophases. In the planar orientation of these mesophases, the elliptical diffusion of the dissolved dyes is visualized by taking several pictures of the sample. The diffusion ratio D// /D is deduced for these columnar mesophases. Furthermore, using a classical optical absorption technique, we present measurements of dye diffusion in the same mesophases. The diffusion constants are measured in two geometries, along and perpendicular to the columns. The diffusion anisotropy ratios are in agreement with those deduced from the ellipse axes. The structure of these new columnar mesophases exhibited by rod-like mesogens is compared with that of disk-like mesogens.     

Rhodamine B diffusion in hair as a probe for structural integrity

The aim of this work was to investigate the diffusion of Rhodamine B into bleached, photo bleached and abraded hair, treated or not with an emulsion of ceramide using two different techniques: spectrophotometry and fluorescence optical microscopy with image analysis. This comparison, combined with the Einstein-Smoluchowski equation, allowed validating a methodology that uses the apparent diffusion coefficient of a dye as an index for hair damage. Distinct behaviors of the dye were observed in the cuticle and in the cortex. For a bleached hair sample the apparent diffusion coefficient in the cuticle ranges from 8.2 x 10(-11) cm2 s(-1) to 10 x 10(-11)cm2 s(-1), while for the cortex this value drops to 4.0 x 10(-11) cm2 s(-1) to 4.2 x 10(-11) cm2 s(-1). The diffusion is always faster in the cuticle than in the cortex and the apparent diffusion coefficient shows up to a seven-fold decrease when the dye penetrates the cortex. The chemical, photochemical and physical treatments applied to hair significantly change the values of the apparent diffusion coefficients in the cuticle. The data also proved that the penetration of Rhodamine B into hair occurs via an intercellular path.