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At least 433 records · Page 24Linked to original sources
PubMed2002

On-chip absorption measurements using an integrated waveguide.

Square hollow waveguides are used to integrate measurement of absorption with chip-based electrophoresis. The 50x50 microm liquid channel and 50x50 microm waveguide are etched as a negative pattern into a silicon master and replicated as a positive in poly-dimethylsiloxane (PDMS). The uniform refractive index of the chip prevents guiding by total internal reflection. Instead, light at 488 nm is guided by reflection at the air-PDMS interface. The waveguide has a 60% efficiency over a distance of 3.2 cm. Separation of fluorescein and the dye BODIPY is demonstrated. A detection limit (S/N=3) of 200 microM fluorescein is obtained using a 50 microm pathlength and a simple photocell detector.

Absorption↗
PubMed2002

Preparation of refractive index matching polymer film alternative to oil for use in a portable surface-plasmon resonance phenomenon-based chemical sensor method.

In order to simplify the procedure for assembling a surface-plasmon resonance (SPR) sensor, a refractive index matching polymer film was prepared as an alternative to the conventionally used matching oil. The refractive index matching polymer film, the refractive index of which was nearly equal to the prism and sensor chip material (a cover glass) of the SPR sensor, was prepared by casting a tetrahydrofuran solution of poly (vinyl chloride) (PVC) containing equal weights of dioctyl phthalate and tricresyl phosphate. The refractive index matching polymer film was found to have a refractive index of 1.516, which is identical to that of the prism and the cover glass used for the present SPR sensor. The utility of the matching polymer film for the SPR sensor was confirmed by the detection of anti-human albumin, based on an antigen-antibody reaction.

Antibodies↗
PubMed2006

Analysis of biosensors by chemically specific optical techniques. Chemiluminescence-imaging and infrared spectroscopic mapping ellipsometry.

The standard methods currently used to read out microarrays are fluorescent and chemiluminescent imaging techniques. These methods require labeling of a component with a marker and, usually, only the concentration of the marker molecule is detected. A label-free imaging method that also enables quantitative spectroscopic analysis of the composition and component interaction would be of great advantage. In this article it is shown for the first time that IR mapping ellipsometry enables label-free imaging of a biochip before and after incubation with peptide solution. The measurements prove that IR ellipsometry is a sensitive tool for laterally resolved identification of the different materials and determination of the composition of a biochip. The lateral resolution required was achieved by using radiation from an infrared synchrotron beamline.

Equipment Design↗
PubMed2000

New low-index liquid refractive index standard: SRM 1922.

A new standard for the calibration of refractometers has been developed. Standard Reference Material (SRM) 1922 is a mineral oil with a refractive index nD = 1.46945 at 20 degrees C, which is within the range of the Brix scale (% sucrose). The change in refractive index with temperature (dn/dT) has been characterized for the range 15 degrees C to 35 degrees C to allow for calibrations within that range of temperatures. The refractive indices were measured at 5 wavelengths in the visible spectrum by using the method of minimum deviation with a +/- 2-3 x 10(-5) uncertainty at 20 degrees C. The values of nD and dnD/dT were determined by fits of a two-term Cauchy function to the values at the measured wavelengths with a +/- 6 x 10(-5) uncertainty in nD at 20 degrees C.

Calibration↗
PubMed2003

Quantitative Brewster angle microscopy of the surface film of human broncho-alveolar lavage fluid.

The morphology, thickness and surface pressure of the surfactant film of broncho-alveoalar lavage (BAL) fluid from patients with sarcoidosis were investigated during spontaneous adsorption of the BAL's surface active material at the air/aqueous buffer interface at 37 degrees C. The biochemical parameters of the BAL fluid determined were protein (Lowry), total phospholipids (from phosphate after ashing) and the individual phospholipids (HPLC). During the spontaneous adsorption of the pulmonary surfactant the surface pressure increased from initially 26 mN/m to 44 mN/m in the equilibrium state. Simultaneously to the increase of the surface pressure, a continuous increase of the reflectivity signal was observed by quantitative Brewster angle microscopy (BAM). The film thickness is calculated from the reflectivity values using an optical model. The effect of the uncertainty of the refractive index, which has to be estimated, is discussed. The BAM images show the inhomogeneous nature of the surfactant film with three distinct phases of different reflectivity, even at relatively low surface pressures. For the brightest phase, the thickness amounts to approximately 12 nm in the equilibrium state of adsorption. This suggests a multilamellar structure. Additionally, we found visual evidence for an adsorption mechanism involving the spreading of vesicles at the interface, in agreement with published results. Differences in the morphology and thickness of the pulmonary surfactant film reported in the literature are obviously due to the varying experimental conditions and materials. We think that the experimental conditions chosen in our study provide a more realistic view of the structure in the lungs in vivo.

Bronchoalveolar Lavage Fluid↗
PubMed2005

Evaluation of rat and rabbit sera lipoproteins in experimentally induced hyperlipidemia by analytical ultracentrifugation.

Animals of various species are widely used as models with which to study atherosclerosis and the lipoprotein metabolism. The objective of this study was to investigate the lipoprotein profiles in Wistar rats and New Zealand white rabbits with experimentally induced hyperlipidemia by means of ultracentrifugation. The Schlieren curves were utilized to compare suckling and adult rat sera to determine whether aging causes alterations in lipoprotein profiles. A striking feature of the data is the high concentration of low-density lipoproteins (LDL), (>5.2 mmol/l cholesterol) in the 2-week old rat serum pool which was greatly decreased in the 3-weeks rat serum pool (<1.3 mmol/l cholesterol). Additional experiments were performed to permit a direct comparison of the amounts of lipoprotein present in rat sera in experimental hyperlipidemia post-Triton WR 1339 administration. Rapid changes in concentrations in very low-density lipoproteins (VLDL), LDL and high-density lipoproteins (HDL) were observed after Triton injection. The administration of Triton WR 1339 to fasted rats resulted in an elevation of serum cholesterol levels. Triton physically alters VLDL, rendering them refractive to the action of lipolytic enzymes in the blood and tissues, preventing or delaying their removal from the blood. Whereas the VLDL concentration was increased markedly, those of LDL and HDL were decreased at 20 h after Triton treatment. Rabbits were fed a diet containing 2% cholesterol for 60 days to develop hyperlipidemia and atheromatous aortic plaques. A combination of preparative and analytical ultracentrifugation was used to investigate of LDL aliquots, to prepare radioactive-labeled lipoproteins and to study induced hyperlipidemia in rabbits. Analytical ultracentrifugation was applied to investigate the LDL flotation peaks before and after cholesterol feeding of rabbits. Modified forms of LDL were detected in the plasma of rabbits with experimentally induced atherosclerosis. ApoB-containing particles, migrating as LDL, intermediate density lipoproteins and VLDL were the most abundant lipoproteins. Gamma camera in vivo scintigraphy on rabbits with radiolabeled lipoproteins revealed visible signals corresponding to atherosclerotic plaques of the aorta and carotid arteries.

Age Factors↗
PubMed2006

[Accuracy of lens power calculation and centration of an aspheric intraocular lens].

BACKGROUND: Aspherical intraocular lenses (IOLs) are presumed to optimize the optical characteristics of IOLs. In order to profit from these characteristics, exact calculation of the IOL power and good centration of the lens are essential. METHODS: In all, 43 eyes of 43 patients with an average age of 70.9+/-8.3 years underwent implantation of a Tecnis IOL (AMO, Ettlingen) after uneventful cataract surgery with topical anesthesia. IOL power calculation was performed using the Holladay, Haigis, and SRK II formulas. Spherical equivalent refraction and centration and position of the implanted IOLs were measured 6 months postoperatively. Centration of the IOL was analyzed using digital slit lamp photographs and an image analysis program. RESULTS: Best corrected visual acuity (BCVA) increased from 0.47+/-0.25 (LogMAR) preoperatively to 0.1+/-0.11 6 months postoperatively (spherical equivalent +0.3+/-0.6 D). The intraindividual difference between target refraction and achieved postoperative refraction was 0.64+/-0.11 D for the Holladay formula, -0.21+/-0.11 D for the Haigis formula, and 0.97+/-0.15 D for the SRK II formula. The mean decentration of the IOL from the center of the corneal limbus was 0.4+/-0.1 mm. CONCLUSIONS: For the aspherical Tecnis IOL very good postoperative functional results are reported, which are supported by an accurate calculation of the IOL power and a good centration of the IOL inside the capsular bag. In this study the Haigis formula showed the lowest difference between target refraction and achieved postoperative refraction.

Aged↗
PubMed2003

Angular and spectral sensitivity of fly photoreceptors. II. Dependence on facet lens F-number and rhabdomere type in Drosophila.

A wave-optical model for the integrated facet lens-rhabdomere system of fly eyes is used to calculate the effective light power in the rhabdomeres when the eye is illuminated with a point light source or with an extended source. Two rhabdomere types are considered: the slender rhabdomeres of R7,8 photoreceptors and the wider, but tapering R1-6 rhabdomeres. The angular sensitivities of the two rhabdomere types have been calculated as a function of F-number and wavelength by fitting Gaussian functions to the effective light power. For a given F-number, the angular sensitivity broadens with wavelength for the slender rhabdomeres, but it stays approximately constant for the wider rhabdomeres. The integrated effective light power increases with the rhabdomere diameter, but it is for both rhabdomere types nearly independent of the light wavelength and F-number. The results are used to interpret the small F-number of Drosophila facet lenses. Presumably the small head puts a limit to the size of the facet lens and favors a short focal length.

Algorithms↗
PubMed2005

Optical quality of the ocular lens of the sea lamprey (Petromyzon marinus) during the mature and transformer periods of life.

While larval sea lampreys exist as eyeless filter feeders for several years, they transform into free-swimming juveniles (transformers) that attach parasitically to prey fish as they develop sexual maturity. This study examines lamprey lens development and optics and, since the lens is often the only refractive component of an aquatic eye, the data also provide an indication of visual ability during transformer and adult periods of life. Seven adult sea lampreys (0.40-0.55 m) and eight transformers (0.15-0.18 m) were sacrificed, the eyes removed and lenses dissected, measured, and placed in an automated laser scanning instrument. Back vertex focal length (spherical aberration) was measured for 14 beam positions across each lens by using a digital camera to record the position of the refracted beam. Transformer lenses exhibit positive spherical aberration, with average focal lengths varying from about 2.40 mm near the lens center and 1.06 mm at the lens periphery. On the other hand, the lenses from adults are largely corrected for spherical aberration, with average focal lengths varying from 2.19 mm to 2.44 mm. This result indicates that the younger lenses do not have a gradient refractive index necessary to mitigate the aberration and that further study of this model may reveal the relation between lens embryology and the development of such a gradient.

Animals↗
PubMed2001

Pseudophakic correction factors for optical biometry.

INTRODUCTION: The IOLMaster of Carl Zeiss Jena, which has recently become available, is a combined instrument for biometry and intraocular lens (IOL) planning for cataract surgery utilizing partial coherence interferometry for measuring axial length. Whereas measurement data from classical ultrasound biometry, e.g. in pseudophakic eyes, need to be corrected by +0.4 to -0.8 mm--depending on the lens material--smaller corrections are expected to be necessary in optical biometry. Correction factors for various modern IOL materials were estimated theoretically and checked in first clinical measurements. METHODS: Starting from the dispersion relation of PMMA and manufacturers' phase refractive index data at 546 nm, the group refractive indices of different IOL materials were estimated for the IOLMaster wavelength of lambda=780 nm. Then, for an average eye of 23.48 mm, the center thicknesses of emmetropizing lenses of different material were calculated. Finally, comparing the pseudophakic optical axial lengths thus deduced with the respective phakic value, individual material-specific correction factors were obtained. RESULTS: Expressing the true axial length ALtrue by the length ALphak measured in phakic mode and a correction factor delta (ALtrue=Alphak+delta), we obtained values of delta=0.12+/-0.01 mm for all IOL materials considered (PMMA, silicone, collamer, AcrySof, MemoryLens). For aphakic eyes, delta=0.20 mm was deduced. DISCUSSION: The calculations suffered from the fact that hardly any information relating to optical material specifications of IOLs is available from lens manufacturers. Therefore, calculations had to be based on--nevertheless realistic--assumptions. Early clinical results support our theoretical findings. Thus, optical biometry seems to be more reliable and forgiving in pseudophakic eyes than classical ultrasound.

Acrylic Resins↗
PubMed2006

Optical properties of ocular tissues in the near infrared region.

Near infrared characterization of optical properties of aqueous humor and vitreous humor of healthy human and bovine eyes has been performed. The indices of refraction (n) of these ocular tissues were determined using a Michelson interferometer. The total diffuse reflection (R (d)) and total transmission (T (t)) measurements had been taken for individual ocular tissue by using a double-integrating sphere setup and infrared laser diodes. The inverse adding doubling (IAD) computational method based on the diffusion approximation and radiative transport theory was applied to the measured values of n, R (d), and T (t) to calculate the optical absorption and scattering coefficients of the human and bovine ocular tissues. The scattering anisotropy value was determined by iteratively running the IAD method program and a Monte Carlo simulation of light-tissue interaction until the minimum difference in experimental and computed value for T (t) was realized. A comparison between the optical characterization of human and bovine ocular samples was also made.

Aged↗
PubMed2005

Optical transillumination tomography for imaging of tissue-engineered blood vessels.

Recent progress in tissue engineering led to the development of completely biological human vessels grown from the patient's own cells. Those tissue-engineered blood vessels (TEBV) are grown on an individual basis at high costs per item, and therefore require close growth monitoring and quality control. We designed and tested an optical transillumination tomography system using red laser light to image weakly scattering specimens, such as TEBV. Fixated TEBV were imaged and the results compared to optical coherence tomography. This preliminary scanner prototype had an in-plane resolution of 50 microm and allowedto see small inhomogeneities and defects in the samples. Tissue attenuation was found to be 70 cm(-1). Main advantages of the transillumination tomography scanner over optical coherence tomography were the inexpensive instrumentation and the potential to rapidly acquire complete 3D sections with a CCD camera. The prototype presented in this study provides a basis to further improve image quality and acquisition speed.

Animals↗
PubMed2005

Effects of refractive index and viscosity on fluorescence and anisotropy decays of enhanced cyan and yellow fluorescent proteins.

The fluorescence lifetime strongly depends on the immediate environment of the fluorophore. Time-resolved fluorescence measurements of the enhanced forms of ECFP and EYFP in water-glycerol mixtures were performed to quantify the effects of the refractive index and viscosity on the fluorescence lifetimes of these proteins. The experimental data show for ECFP and EYFP two fluorescence lifetime components: one short lifetime of about 1 ns and a longer lifetime of about 3.7 ns of ECFP and for EYFP 3.4. The fluorescence of ECFP is very heterogeneous, which can be explained by the presence of two populations: a conformation (67% present) where the fluorophore is less quenched than in the other conformation (33% present). The fluorescence decay of EYFP is much more homogeneous and the amplitude of the short fluorescence lifetime is about 5%. The fluorescence anisotropy decays show that the rotational correlation time of both proteins scales with increasing viscosity of the solvent similarly as shown earlier for GFP. The rotational correlation times are identical for ECFP and EYFP, which can be expected since both proteins have the same shape and size. The only difference observed is the slightly lower initial anisotropy for ECFP as compared to the one of EYFP.

Bacterial Proteins↗
PubMed2005

Micrometer-scale particle sizing by laser diffraction: critical impact of the imaginary component of refractive index.

PURPOSE: This study evaluated the effect of the imaginary component of the refractive index on laser diffraction particle size data for pharmaceutical samples. METHODS: Excipient particles 1-5 microm in diameter (irregular morphology) were measured by laser diffraction. Optical parameters were obtained and verified based on comparison of calculated vs. actual particle volume fraction. RESULTS: Inappropriate imaginary components of the refractive index can lead to inaccurate results, including false peaks in the size distribution. For laser diffraction measurements, obtaining appropriate or "effective" imaginary components of the refractive index was not always straightforward. When the recommended criteria such as the concentration match and the fit of the scattering data gave similar results for very different calculated size distributions, a supplemental technique, microscopy with image analysis, was used to decide between the alternatives. Use of effective optical parameters produced a good match between laser diffraction data and microscopy/image analysis data. CONCLUSIONS: The imaginary component of the refractive index can have a major impact on particle size results calculated from laser diffraction data. When performed properly, laser diffraction and microscopy with image analysis can yield comparable results.

Excipients↗
PubMed2005

3D-resolved investigation of the pH gradient in artificial skin constructs by means of fluorescence lifetime imaging.

PURPOSE: The development of substitutes for the human skin, e.g., artificial skin constructs (ASCs), is of particular importance for pharmaceutical and dermatologic research because they represent economical test samples for the validation of new drugs. In this regard, it is essential for the skin substitutes to be reliable models of the genuine skin, i.e., to have similar morphology and functionality. Particularly important is the barrier function, i.e., the selective permeability of the skin, which is strongly related to the epidermal pH gradient. Because the pH significantly influences the permeation profile of ionizable drugs such as nonsteroidal anti-inflammatory drugs, it is of major importance to quantitatively measure the epidermal pH gradient of the ASC and compare it to that of genuine skin. METHODS: Using three-dimensional fluorescence lifetime imaging combined with two-photon scanning microscopy, we measured with submicron resolution the three-dimensional pH gradient in the epidermis of ASCs stained with 2',7'-bis-(2-carboxyethyl)-5/6-carboxyfluorescein. RESULTS: Similar to genuine skin, the surface of the artificial epidermis has an acidic character (pH 5.9), whereas in the deeper layers the pH increases up to 7.0. Moreover, the pH gradient differs in the cell interior (maximally 7.2) and in the intercellular matrix (maximally 6.6). Apart from the similitude of the pH distribution, the genuine and the artificial skin prove to have similar morphologies and to be characterized by similar distributions of the refractive index. CONCLUSIONS: Artificial skin is a reliable model of genuine human skin, e.g., in permeability studies, because it is characterized by a similar pH gradient, a similar morphology, and a similar distribution of the refractive index to that of genuine skin.

Fluoresceins↗
PubMed2006

Dense gas processing of micron-sized drug formulations incorporating hydroxypropylated and methylated beta-cyclodextrin.

PURPOSE: Because of their importance in pharmaceutical applications, hydroxypropyl-beta-cyclodextrin and methyl-beta-cyclodextrin have been selected to study the formation of micronized complexes incorporating active pharmaceutical ingredients (APIs) and cyclodextrins (CDs) by dense gas (DG) processing. METHODS: A single-step DG technique was used as an alternative to conventional methods for the manufacturing of API/CD complexes. The DG technology is highly attractive in the pharmaceutical industry because of its potential to generate micronized particles with controlled particle size distributions at moderate operating conditions. The effect of the aerosol solvent extraction system (ASES) processing on the dissolution performance of naproxen (NPX) was examined. RESULTS: The CDs were produced as microspheres smaller than 3 microm. The coprecipitation of each CD with NPX resulted in the production of microparticles with enhanced dissolution rates. CONCLUSIONS: The ASES was operated under mild conditions and generated micron-sized spherical particles that could be of particular interest in formulations for pulmonary delivery. Particular advantages of the technique are that (1) nontoxic solvents are used, and (2) it is suitable for the processing of thermally labile compounds. The proposed process can create opportunities to improve current administration routes and exploit novel delivery systems for drug formulations incorporating CDs.

2-Hydroxypropyl-beta-cyclodextrin↗
PubMed1997

The relationship between the structure of monoalkyl branched saturated triacylglycerols and some physical properties.

Three different physical properties, the gel point ("solidification point"), the refractive index and the density, were determined and related to the structure of the branched triacylglycerols. A four-factor central composite face-centered design was constructed where the four variables were the length of the main chain, the branching position, the length of the side chain, and the number of branched fatty acyl groups attached to the glycerol backbone. Second-order models were calculated in which the three physical properties were related to the structure. Four additional branched triacylglycerols were analyzed in order to confirm the validity of each model. Contour plots are shown in order to visualize the prediction equations which were obtained.

Fatty Acids↗