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At least 775 records · Page 43Linked to original sources
PubMed2006

Polarization-dependent effects in surface-enhanced Raman scattering (SERS).

A few key examples of polarization effects in surface-enhanced Raman scattering (SERS) are highlighted and discussed. It is argued that the polarization of the local field, which is felt by an analyte molecule in a location of high electromagnetic field enhancement (hot-spot), can be very different from that of the incident exciting beam. The polarization dependence of the SERS signal is, therefore, mostly dictated by the coupling of the laser to the plasmons rather than by the symmetry of the Raman tensor of the analyte. This sets serious restrictions for the interpretation of both single-molecule SERS polarization studies and for the use of circularly polarized light in techniques like surface-enhanced Raman optical activity.

Artifacts↗
PubMed2002

Evaluation of meningococcal C oligosaccharide conjugate vaccines by size-exclusion chromatography/multi-angle laser light scattering.

The mean molecular masses of three different meningococcal C saccharide (MenC)-protein conjugate vaccines and their constituent proteins were estimated using HPLC size-exclusion chromatography (SEC) with multi-angle laser light scattering (MALLS) and refractive-index (RI) detection (SEC/MALLS). Chromatography of two CRM(197) conjugates (MenC-CRM(197)-A and MenC-CRM(197)-B) and one tetanus toxoid (TT) conjugate (MenC-TT) was performed in PBS, pH 7.4, on TSK-Gel (TosoHaas) analytical columns [CRM(197) is a non-catalytic cross-reacting mutant (CRM) of diphtheria toxin]. Analysis of the light-scattering signal measured at 18 angles simultaneously, using the RI signal as a measure of concentration, gave absolute weight-average-molecular-mass (M(w)) values for the CRM(197) conjugates as follows: MenC-CRM(197)-A, approximately 75,000 g x mol(-1) and MenC-CRM(197)-B, approximately 350,000 g x mol(-1), suggesting that MenC-CRM(197)-A is a monomer (one carrier protein per conjugate molecule), while MenC-CRM(197)-B is largely composed of conjugates containing three or four CRM(197) molecules. The MenC-TT conjugate eluted as a two-component system with (M(w)) of 1.63 x 10(6) and 395,000 g x mol(-1), suggesting that some cross-linked complexes contain up to six TT molecules. Comparison of results from MALLS/RI with those obtained using UV detection highlights the differences in size and relative composition of the various subpopulations of the MenC conjugates that can be obtained using different detection systems.

Bacterial Proteins↗
PubMed1984

The effect of guanidinium chloride on the behaviour of human cervical-mucus glycoproteins. Evidence for unfolding regions of ordered structure in 6M-guanidinium chloride.

The macromolecular properties of cervical-mucus glycoproteins (mucins) were studied as a function of the concentration of guanidinium chloride with conventional light-scattering, photon-correlation spectroscopy and sedimentation-velocity centrifugation. No evidence for an association of the mucins in 0.2M-NaCl as compared with 6M-guanidinium chloride was found at mucin concentrations below approx. 0.5 mg/ml. However, an increase in the frictional coefficient and in the radius of gyration occurred with increasing concentrations of guanidinium chloride, in particular between 4 M and 6 M, suggesting an expansion of the individual macromolecule. The change in the particle-scattering function is consistent with a transition from a 'stiff' random coil in 0.2 M-NaCl into a more flexible one in 6 M-guanidinium chloride. We suggest that the mucins contain regions of 'ordered' structure which can undergo a reversible 'unfolding' analogous to the behaviour of a conventional globular protein exposed to a denaturing solvent. Such regions might carry sites for specific interactions between mucins and/or be decisive for their conformation and macromolecular properties in physiological solvents.

Cervix Mucus↗
PubMed1996

Dispersion, aberration and deconvolution in multi-wavelength fluorescence images.

The wavelength dependence of the incoherent point spread function in a wide-field microscope was investigated experimentally. Dispersion in the sample and optics can lead to significant changes in the point spread function as wavelength is varied over the range commonly used in fluorescence microscopy. For a given sample, optical conditions can generally be optimized to produce a point spread function largely free of spherical aberration at a given wavelength. Unfortunately, deviations in wavelength from this value will result in spherically aberrated point spread functions. Therefore, when multiple fluorophores are used to localize different components in the same sample, the image of the distribution of at least one of the fluorophores will be spherically aberrated. This aberration causes a loss of intensity and resolution, thereby complicating the localization and analysis of multiple components in a multi-wavelength image. We show that optimal resolution can be restored to a spherically aberrated image by constrained, iterative deconvolution, as long as the spherical aberration in the point spread function used for deconvolution matches the aberration in the image reasonably well. The success of this method is essentially independent of the initial degree of spherical aberration in the image. Deconvolution of many biological images can be achieved by collecting a small library of spherically aberrated and unaberrated point spread functions, and then choosing a point spread function appropriate for deconvolving each image. The co-localization and relative intensities of multiple components can then be accurately studied in a multi-wavelength image.

Algorithms↗
PubMed2000

Analysis of spherical aberration of a water immersion objective: application to specimens with refractive indices 1.33-1.40.

The method of using immersion medium to correct spherical aberration for water immersion objectives when the samples are not water is investigated. Spherical aberration is measured by an interferometer converted from a confocal microscope for samples with different refractive indices. When the proper refractive index of the immersion medium and thickness of cover slip are selected, the measured spherical aberration approaches zero. A theoretical model can be used for prediction of the immersion medium to correct spherical aberration for various samples. Using the thinnest available cover slip (100 microm), the zero spherical aberration condition can be applied to samples with refractive index as high as 1.40. Confocal images in the condition of almost no spherical aberration are included to demonstrate the improvement of axial resolution due to this correction.

Cheek↗
PubMed2000

Strategies for the compensation of specimen-induced spherical aberration in confocal microscopy of skin.

We consider various strategies for confocal imaging of human skin which seek to reduce the effects of the specimen-induced aberrations. We calculate the spherical aberration introduced by the stratified structure of skin and show how the confocal signal is affected when attempting to image at various depths within the dermis. Using simple methods it is shown how images might be improved by compensating for the induced aberration. The methods include the use of an iris to reduce the pupil area, changing the refractive index of the immersion medium and using a lens with variable coverglass correction.

Artifacts↗
PubMed2003

A prism combination for near isotropic fluorescence excitation by total internal reflection.

Total internal reflection fluorescence (TIRF) microscopy is finding increasing application for selectively detecting molecules at or near a glass-water surface. As with all fluorescence methods, the efficiency of excitation of a fluorophore is potentially sensitive to the polarization state of the source. In TIRF, s-polarized excitation produces an evanescent field that is perpendicular to the incident plane (y direction), whereas p-polarized light generates a more complex pattern but one dominated by a field that is vertical to the surface (z direction). Thus, fluorophores whose absorption dipoles are fixed in the x direction are not favourably aligned for excitation. Here we describe a beam-splitting prism arrangement that allows excitation by two orthogonal beams, thus giving isotropic excitation in the x-y plane with s-polarized light. With linearly polarized light at the magic angle, near isotropic excitation in three dimensions should be achieved. This prism design should find application in polarized fluorescence microscopy to investigate the rotational motions of macromolecules or to minimize flickering of fluorescence emission arising from molecular rotations in single molecule studies.

Fluorescence Polarization↗
PubMed2003

Variable-angle total internal reflection fluorescence microscopy (VA-TIRFM): realization and application of a compact illumination device.

A novel compact illumination device in variable-angle total internal reflection fluorescence microscopy (VA-TIRFM) is described. This device replaces the standard condensor of an upright microscope. Light from different laser sources is delivered via a monomode fibre and focused onto identical parts of a sample under variable angles of total internal reflection. Thus, fluorophores in close proximity to a cell-substrate interface are excited by an evanescent wave with variable penetration depth, and localized with high (nanometre) axial resolution. In addition to quantitative measurements in solution, fluorescence markers of the cytoplasm and the plasma membrane, i.e. calcein and laurdan, were examined using cultivated endothelial cells. Distances between the glass substrate and the plasma membrane were determined using the mathematical algorithm of a four-layer model, as well as a Gaussian-shaped intensity profile of the illumination spot on the samples. Distances between 0 and 30 nm in focal contacts and between 100 and 300 nm in other parts of the cell were thus determined. In addition to measurements of cell-substrate topology, the illumination device appears appropriate for numerous applications in which high axial resolution is required, e.g. experiments on endocytosis or exocytosis, as well as measurements of ion concentrations proximal to the plasma membrane. The compact illumination device is also suitable for combining TIRFM with further innovative techniques, e.g. time-resolved fluorescence spectroscopy, fluorescence lifetime imaging (FLIM) or fluorescence resonance energy transfer (FRET).

2-Naphthylamine↗
PubMed2001

Use of optical coherence tomography for assessment of dental caries: quantitative procedure.

A method for quantitative assessment of dental caries using optical coherence tomography (OCT) was demonstrated. Development of caries lesions in 15 bovine teeth, by demineralization in acidic buffer solution, was quantitatively assessed daily for 3 days, using OCT. An OCT system which can collect A-scans (depth versus reflectivity curve), B-scans (longitudinal images) and C-scans (transverse images at constant depth) was used. While the B- and C-scans qualitatively described the lesion detected, the A-scan which showed the depth (mm) resolved reflectivity (dB) of the tooth tissue was used for the quantitative analysis. After a simple normalization procedure to determine the actual depth the light travelled into the tooth tissue, the area (R) under the A-scan was quantified as a measure of the degree of reflectivity of the tissue. The result showed that R (dB mm) decreased with increasing demineralization time. The percentage reflectivity loss (R%) in demineralized tissue, which related to the amount of mineral loss, was also calculated, and it was observed that R% increased with increasing demineralization time. It was concluded that with the above procedure, OCT could quantitatively monitor the mineral changes in a caries lesion on a longitudinal basis.

Animals↗
PubMed1999

Numerical study of the influence of the shell structure of the crystalline lens on the refractive properties of the human eye.

In this paper, the numerical model of the refractive properties of the human eye is given. A special account is given of the laminated structure of the crystalline lens. The crystalline lens is presented in the form of hundreds of shells with rotational symmetry, and with the refractive index constant within each shell. The shells have the form of two semi-ellipsoids joined along the equator. The refractive index increases from the cortical shell to the inner one, according to the exponential dependency. The cornea, approximated by two ellipsoidal surfaces, is added in front of the crystalline lens. A ray-tracing procedure is applied to study the refractive properties of such a system: refractive power, spherical aberration and energy distribution. The optical properties of the given model are analysed by changing some parameters such as refractive index profile and number of shells. Calculations show that the gradient of the refractive index inside the crystalline lens results in the generation of many focal planes in such an optical system.

Computer Simulation↗
PubMed1999

A longitudinal study of cycloplegic refraction in a cohort of 350 Japanese schoolchildren. Anisometropia.

The intereye difference of cycloplegic refraction was determined in a cohort of 350 rural Japanese schoolchildren aged 6 to 11 years. The intereye spherical difference remained statistically unchanged throughout 5 years, with mean value ranging from 0.21 to 0.28 D, median from 0.15 to 0.20 D, and the 95th percentile from 0.58 to 0.85 D. The prevalence of 1.0 D or greater spherical anisometropia was up to 3.1%. Linear regression analyses of the longitudinal data from individual children revealed that 295 (84.3%) children and remained unchanged while 55 (15.7%) showed significant increase or decrease in the amount of anisometropia with increasing age. The intereye astigmatic difference was also statistically unchangeable, with mean value ranging from 0.28 to 0.36 D, median from 0.20 to 0.39 D, and the 95th percentile from 0.70 to 0.90 D. The prevalence of 1.0 D or greater astigmatic anisometropia was up to 4.3%. There was a significant correlation between the spherical and astigmatic anisometropia. The results show the current state of intereye refractive difference in Japanese schoolchildren, demonstrating that it remains unchanged and significant anisometropia is rare during school age.

Anisometropia↗
PubMed1999

A longitudinal study of cycloplegic refraction in a cohort of 350 Japanese schoolchildren. Cycloplegic refraction.

We performed a 5 year longitudinal study of cycloplegic refraction in a cohort of 350 Japanese schoolchildren from 6 to 11 years of age in a rural area of southwestern Japan. The spherical refraction was measured under cycloplegia with an infrared autorefractometer. The grouped data from 350 right eyes showed leptokurtic frequency distributions, and the median was +0.91 D at age 6 yrs, shifted towards emmetropia with increasing age and reached +0.34 D at age 11 years. The prevalence of myopia of -1.0 D or more was 0.3%, 0.6%, 2.0%, 2.6%, 2.9%, and 4.9% from age 6 to 11 years, and the prevalence of myopia of more than -2.0 D was less than 1% at age 6-9 years and thereafter increased up to 6.0% at age 11 years. Linear regression analysis for the longitudinal refractive data revealed that 247 (70.6%) of the 350 eyes exhibited first-order linear decrease in hyperopia or increase in myopia with an average annual change of -0.15 D/year, 14 (4%) showed second-order curvilinear change, and 89 (25.4%) remained unchanged. In the eyes with linear change, there was a significant relationship between the refraction at age 6 years and the rate of subsequent change such that the less hyperopic or emmetropic at age 6 years, the larger the change. The refraction at birth was estimated by extrapolation of the linear regression analysis results, implying that 88% of newborns have hyperopia of +1.0 D or greater and myopia is rare. These results indicate the current state of refraction in Japanese schoolchildren of a rural area.

Child↗
PubMed2003

The assessment of automated measures of hydrogel contact lens refractive index.

PURPOSE: To investigate within- and between-operator reliability and validity of refractive index measures of hydrogel lenses. METHODS: Twenty-three lenses of various nominal water contents were examined by two operators on two occasions separated by 1 h. An automated refractometer (CLR 12-70, Index Instruments, Cambridge, UK) was used for refractive index measures. Lenses were presented in a random order to each operator by a third party, and operators were masked to any potential lens identifiers. Intraclass correlation coefficients (ICC), 95% limits of agreement (LoA), and paired t-tests were used to characterize the within- and between-operator reliability and validity of lens refractive index measures. RESULTS: The mean (+/-S.D.) difference between sessions was 0.0001 +/- 0.0011, which did not significantly differ from zero (p = 0.64). Within-operator reliability was excellent (ICC = 0.9990, 95% LoA = -0.0021 to 0.0024). The mean (+/-S.D.) difference between-operators was 0.0002 +/- 0.0010, which was not significantly different from zero (p = 0.54). Between-operator reliability was also excellent (ICC = 0.9984, 95% LoA = -0.0026 to 0.0029). The mean difference between the nominally reported refractive index and our refractive index measures was -0.0009 +/- 0.082, which did not differ statistically from zero (p = 0.52); the 95% LoA for this difference was -0.0152 to 0.0169. CONCLUSION: There is good reliability within- and between-operators in measuring the refractive index of hydrogel lenses using the CLR 12-70 automated refractometer.

Contact Lenses, Hydrophilic↗
PubMedDate not supplied

Use of the refractive index to measure the adequacy of glycerol removal from previously frozen erythrocytes.

A common method for measuring deglycerolization of previously frozen erythrocytes is to determine the osmolality of the supernatant fluid after completion of the wash cycle. We attempted to compare this type of examination with the simpler, faster, and cheaper determination of refractive index (RI) using the Goldberg refractometer. One hundred twenty units of deglycerolized red blood cells, some with glycerol added so as to exceed an acceptable 1% glycerol content, had measurements made of the post-wash supernatant fluid by refractive index and osmometry. The responsiveness of refractive index to residual glycerol was essentially the same as osmolality. Although there is more interference from supernatant hemoglobin, this did not preclude the use of RI to measure glycerol removal. Readings up to 28 had glycerol levels of less than 1%. Readings between 29 and 31 should be checked by osmometry, and readings over 31 should cause the unit of blood to be rejected.

Buffers↗
PubMedDate not supplied

Rapid estimation of the glycerol concentration of frozen-thawed red cells prepared by the agglomeration technique.

The glycerol concentration of frozen-thawed red cells must be less than 2 percent to prevent hemolysis upon transfusion. Three methods were investigated for monitoring the glycerol concentration of frozen-thawed red cells prepared by the agglomeration technique. The supernatant osmolality and glycerol concentration were determined on 47 units of frozen-thawed red cells prepared by agglomeration, and were found to be linearly related (r = 0.83, p less than 0.001). The supernatant refractive index was determined on 29 of the same units. There also was a linear relationship between the refractive index and the glycerol concentration (r = 0.74, p less than 0.001). The relationships were different from those previously reported for red cells prepared by other methods. The simulated transfusion test was done on red cells from three units whose glycerol concentration had been artificially elevated. The simulated transfusion test was found to be sensitive to glycerol concentrations above 2 percent. All three of the methods evaluated can be used to estimate the glycerol concentration of frozen-thawed red cells prepared by the agglomeration technique.

Erythrocytes↗
PubMed2005

Silica microspheres for biomolecular detection applications.

Microsphere-based biosensors have been attracting the attention of the photonics community due to their high sensitivity, selectivity and implementation. Microspheres, with their high quality-factor (Q-factor) morphology dependent resonances, are very sensitive to refractive index and size changes. The perturbation of the microsphere morphology dependent resonances can be used for the detection of biomolecules. Adsorption of different biomolecules on the surface of microspheres causes a change of effective size and refractive index leading to the shift of resonance wavelengths. A biosensor, based on this phenomenon, can detect a single molecule sensitively depending on the configuration that needs to be designed and optimised. Silica with a refractive index of 1.5, which is very close to that of bimolecular agents, is a suitable photonic material to use for biosensing applications. The transverse electric and transverse magnetic elastic scattering spectra at 90 degrees and 0 degrees are calculated at 1.55 microm with the associated shifts after adding a layer on it. 90 degrees scattering is used to monitor the scattered signal, whereas 0 degrees scattering is used to monitor the transmission signal.

Biopolymers↗
PubMed2005

[Accuracy of the autorefractor power refractor in clinical work--a comparative study].

BACKGROUND: The aim of this prospective study was to investigate accuracy and efficiency of the autorefractometer PowerRefractor compared to established autorefractometers and retinoscopy as standard method. PATIENTS AND METHODS: 150 patients (300 eyes) were examined. Patients were initially (pupil not influenced) analyzed with the Power Refractor (PR (neutral)). After that a examination followed under standardized Cyclopentolat cycloplegia with the Power Refractor (PR (cyclo)), the hand-held Retinomax K-plus (Nikon), the table-top mounted RK-5 (Canon) and retinoscopy. RESULTS: Deviation from retinoscopy (percentage of values with more than 1 dpt difference/maximal deviation): Sphere: PR (neutral): 66.3 %/8.5 dpt; PR (cyclo): 48 %/5 dpt; RK-5: 26.7 %/4.75 dpt; Retinomax K-plus: 6.7 %/1.25 dpt; Cylinder: PR (neutral): 12 %/6.25 dpt; PR (cyclo): 21 %/4.75 dpt; RK-5: 1.3 %/2.75 dpt; Retinomax K-plus: 2.3 %/2.5 dpt; spherical equivalent: PR (neutral): 44.7 %/7.1 dpt; PR (cyclo): 35.3 %/5.4 dpt; RK-5: 9 %/4.5 dpt; Retinomax K-plus: 1.3 %/1.,4 dpt; error of entire refraction: PR (neutral): 62.7 %/7.8 dpt; PR (cyclo): 61.3 %/7.3 dpt; RK-5: 24 %/4,5 dpt; Retinomax K-plus: 14.7 %/3.6 dpt CONCLUSIONS: The best accuracy compared to retinoscopy had Retinomax K-plus followed by RK-5. PowerRefractor had the biggest deviations of the tested devices. PowerRefractor may be a usefull device for screening small children and handicapped people because of the one meter observing distance. For a precise refraction especially in children a retinoscopy under cycloplegic conditions is still necessary.

Adolescent↗