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At least 181 records · Page 10Linked to original sources
PubMed1999

Multiwavelength spectrophotometric determination of acid dissociation constants: Part III. Resolution of multi-protic ionization systems.

A multiwavelength spectrophotometric (WApH) titration method was applied to study several multi-protic histamine H2-receptor antagonists which involved four acid dissociation constants (pKa values) over the pH range of 2-10. Specifically, UV absorption spectra of the drug solution were acquired in the course of a pH-metric titration using an optical device based on a fibre optics dip probe, a light source and a diode array detector. Target factor analysis was utilized to deduce the pKa values from the spectral data recorded at different pH. It was noted that some of the pKa values were within mid pH range which were difficult to obtain because of insufficient absorption spectra acquired in the un-buffered region of the titration curve. With the aid of the WApH technique coupled with an optically transparent buffer, all pKa values have been successfully determined and were in excellent agreement with those measured using a conventional pH-metric method.

Algorithms↗
PubMed2002

Water-soluble and optically pH-sensitive single-walled carbon nanotubes from surface modification.

There is great interest in using single-walled carbon nanotubes (SWNTs) as nanoscale probes and sensors in biological electronics and optical devices because the electronic and optical properties of SWNTs are extremely sensitive to the surrounding environments. A well-controlled modification of SWNT surfaces may provide unique interfaces that are sensitive to the biological variables such as pH, glucose, various ions and proteins. In this paper, we report a facile chemical routine to prepare water-soluble SWNTs that still retain their van Hove singularities after acid oxidative treatment. The aqueous solutions (0.03-0.15 mg/mL) are stable for more than a month. The solubility in water for as-treated SWNTs with surfaces modified by carboxylate groups provides us with a unique opportunity to reveal the relationship of the SWNT electronic and optical properties with pH. Here we present the first observation that after surface modification with carboxylate groups, the optical absorption of the first interband transition of as-treated water-soluble semiconducting SWNTs reversibly responds to the pH change in aqueous solutions. Our results indicate that surface modification of SWNTs is a promising way for preparing chemically selective SWNT interfaces, which may open new exciting opportunities for various applications.

Biosensing Techniques↗
PubMed2001

Enhanced Kerr nonlinearity via atomic coherence in a three-level atomic system.

We measure the Kerr-nonlinear index of refraction of a three-level Lambda-type atomic system inside an optical ring cavity. The Kerr nonlinearity is modified and greatly enhanced near atomic resonant conditions for both probe and coupling beams. The Kerr nonlinear coefficient n(2) changes sign when the coupling beam frequency detuning switches sign, which can lead to interesting applications in optical devices such as all-optical switches.

Journal Article↗
PubMed1997

Diagnostic embryoscopy and fetoscopy in the first trimester of pregnancy.

Embryoscopy is the examination of the embryo at 9-10 weeks' gestation through the intact membranes by introducing an endoscope into the exocoelomic space transcervically or transabdominally. This is likely to remain confined to the management of early pregnancy in selected families affected by recurrent genetic syndromes with recognizable external fetal abnormalities. The procedure-related risk of fetal loss is around 12 per cent. Fetoscopy is the examination of the fetus after 11 weeks' gestation. This is performed transabdominally in the amniotic fluid. The technique has evolved with the miniaturization of the optical device by using fibre-optics technology. This procedure is likely to find new applications with the development of ultrasound examination at 10-14 weeks' gestation in order to, either confirm, or rule out suspected external fetal abnormalities. Amniocentesis can be performed at the same time. The procedure-related risk is likely to remain below 10 per cent but no accurate figures can be drawn from the literature.

Amniocentesis↗
PubMed2003

Multicolor luminescence patterning by photoactivation of semiconductor nanoparticle films.

Indiscriminate adsorption of nanoparticles (NPs) significantly complicates the preparation of mesoscale NP patterns considered as enabling technology for many devices and processes. Instead of selected chemical functionalization of the substrate surface prior to the assembly of nanocolloids, the required optical properties - in our case, high quantum yield luminescence - are imparted to the layer-by-layer assembled films by spatially selected photoactivation. The films are made by sequential adsorption of a positively charged polyelectrolyte and a negatively charged CdSe/CdS aqueous dispersion with an initial quantum yield of 0.5-2%. The photoactivation process takes place in the presence of oxygen and may be accompanied by photoetching. A 50-500-fold increase in the luminescence intensity of CdSe/CdS citrate-stabilized particles (quantum yield 25-45%) after visible light illumination provides excellent pattern contrast. Micron scale luminescence patterns were produced from NPs of various CdSe core diameters with red, yellow, and green emission. It was also demonstrated that different emission colors such as orange and green can be combined in one image by taking advantage of spatially selective photoetching. The presented optical patterning technique significantly simplifies the preparation of luminescence patterns as compared to conventional methods. The high signal-to-noise ratio associated with it is essential for optical devices, information processing, and biophotonics. The most immediate use of this approach is expected in cryptography and cell monitoring.

Cadmium Compounds↗
PubMed1986

Non-optical aids.

Non-optical aids help patients deal with everyday problems where sight is impaired. A review of the many non-optical devices is discussed including relative size devices, writing and communication aids, posturing and positioning aids, illumination control and non-optical sensory substitution devices. An extensive appendix is provided listing sources of many non-optical aids.

Blindness↗
PubMed2006

Bright luminescence from silane substituted and bridged silicon nanoclusters.

Time-dependent density functional theory (TDDFT) calculations show that silicon nanoclusters (Si-NC) capped by linear silane groups have large oscillator strengths of the same magnitude as reported in recent experimental studies. We propose a mechanism where linear silanes attached to the Si-NC surface affect the optical properties enhancing the oscillator strengths and thereby accounting for the bright luminescence observed in the blue region of the visible spectrum. The anisotropic emission seen experimentally can also be explained by the presence of the silane groups on the cluster surface. The excitation energies are found to be only slightly affected by the silanes, whereas the oscillator strengths increase with the length of the silane chain and are significantly larger than obtained for unsubstituted Si-NCs. In TDDFT studies of Si-NC dimers interconnected by a linear silane bridge, we obtained large oscillator strengths indicating that such structures could be useful light sources for optical devices.

Computer Simulation↗
PubMed2006

Compact soft x-ray transmission microscopy with sub-50 nm spatial resolution.

In this paper, the development of compact transmission soft x-ray microscopy (XM) with sub-50 nm spatial resolution for biomedical applications is described. The compact transmission soft x-ray microscope operates at lambda = 2.88 nm (430 eV) and is based on a tabletop regenerative x-ray source in combination with a tandem ellipsoidal condenser mirror for sample illumination, an objective micro zone plate and a thinned back-illuminated charge coupled device to record an x-ray image. The new, compact x-ray microscope system requires the fabrication of proper x-ray optical devices in order to obtain high-quality images. For an application-oriented microscope, the alignment procedure is fully automated via computer control through a graphic user interface. In imaging studies using our compact XM system, a gold mesh image was obtained with 45 nm resolution at x580 magnification and 1 min exposure. Images of a biological sample (Coscinodiscus oculoides) were recorded.

Diatoms↗
PubMed2006

High-speed fabrication of patterned colloidal photonic structures in centrifugal microfluidic chips.

In this paper, we report a rapid and facile method for fabricating colloidal photonic crystals inside microchannels of radially symmetric microfluidic chips which were made using soft-lithography. As the suspension of monodisperse silica or polystyrene latex spheres was driven to flow through the channels under the action of centrifugal force, the colloidal spheres were quickly assembled into face centered cubic arrangement which had a few photonic stop bands. The soft-microfluidic channels and cells confined the colloidal crystals into designed patterns. The optical reflectance was modulated by the refractive-index mismatch between the colloidal particles and the solvent in the interstices between the particles. Therefore, the present microfluidic chips with built-in colloidal photonic crystals can be used as in-situ optofluidic microsensors for high throughput screening or light filters in integrated adaptive optical devices.

Colloids↗
PubMed2001

Light field propagation by metal micro- and nanostructures.

The ability to sustain plasmon oscillations gives rise to unique properties of metal nanostructures, which can be exploited for the controlled manipulation of light fields on the nanoscale. In this context we investigate electromagnetic coupling effects within lithographically produced ensembles of gold nanoparticles with a photon scanning tunnelling microscope. To provide an interface between these nano-optical devices and classical far-field optics, we investigate surface plasmon propagation on microstructured metal thin films.

Journal Article↗
PubMed1999

Bleaching of bacteriorhodopsin by continuous light.

A new two step photobleaching process is observed under continuous illumination of bacteriorhodopsin. This photobleaching is considerable even at physiological temperatures and becomes large at 50-60 degrees C. The photobleaching also increases with increasing pH from 7 to 10. We suggest that the bleaching at its final stage could be due to the dissociation of the retinal and a local thermal denaturation-like process. These facts may question the generally held belief that BR is a stable protein in vivo for a long period of time. Our results may have relevance also to practical applications of bacteriorhodopsin where the stability of bacteriorhodopsin is a key issue. In certain instances, the use of bacteriorhodopsin may require cooled conditions. Here, we defined the conditions under which bacteriorhodopsin is stable. The permanent photobleaching offers a new way of picture imaging and information input for bacteriorhodopsin-based optical devices.

Bacteriorhodopsins↗
PubMedDate not supplied

Laser hair removal.

Since 1996, there have been numerous advances in hair laser removal that utilize melanin as a chromophore. All of the devices on the market may be used in patients with light skin (phototypes I-III) and yield hair reduction near 75%. The ruby (694 nm) laser, alexandrite (755 nm) laser, and diode (810 nm) laser, as well as intense pulsed light are commonly used devices for hair laser removal. The long-pulsed Nd:YAG (1064 nm) laser represents the safest device for hair removal in dark-skinned patients because of its long wavelength, although the diode laser, alexandrite laser, and intense pulse light may be used. For treatment of light hair, combination radiofrequency and optical devices as well as photodynamic therapy are under investigation.

Equipment Design↗
PubMedDate not supplied

Autofluorescence methods in ophthalmology.

An overview of the fluorophores of the eye, the methods used to measure ocular fluorescence, and the existing or ready-to-market instrumentation for the early diagnosis and monitoring of ophthalmic pathologies is presented. Emphasis is given to the impact that a more detailed knowledge of the fluorophores of the eye, their age and pathology relationship, and the considerable technology-driven progress in optical devices and components has had on the development of new compact yet powerful instruments for population screening and for patient follow-ups, using fluorometry alone or in combination with other optical techniques such as light scattering.

Diagnostic Techniques, Ophthalmological↗
PubMed2006

Organic-inorganic hybrid mesoporous silicas: functionalization, pore size, and morphology control.

Topological design of mesoporous silica materials, pore architecture, pore size, and morphology are currently major issues in areas such as catalytic conversion of bulky molecules, adsorption, host-guest chemistry, etc. In this sense, we discuss the pore size-controlled mesostructure, framework functionalization, and morphology control of organic-inorganic hybrid mesoporous silicas by which we can improve the applicability of mesoporous materials. First, we explain that the sizes of hexagonal- and cubic-type pores in organic-inorganic hybrid mesoporous silicas are well controlled from 24.3 to 98.0 A by the direct micelle-control method using an organosilica precursor and surfactants with different alkyl chain lengths or triblock copolymers as templates and swelling agents incorporated in the formed micelles. Second, we describe that organic-inorganic hybrid mesoporous materials with various functional groups form various external morphologies such as rod, cauliflower, film, rope, spheroid, monolith, and fiber shapes. Third, we discuss that transition metals (Ti and Ru) and rare-earth ions (Eu(3+) and Tb(3+)) are used to modify organic-inorganic hybrid mesoporous silica materials. Such hybrid mesoporous silica materials are expected to be applied as excellent catalysts for organic reactions, photocatalysis, optical devices, etc.

Fluorescence↗
PubMed2001

Growth, optical spectroscopy and crystal field investigation of YAl3(BO3)4 single crystals doped with tripositive praseodymium.

Single crystals of YAl3(BO3)4 doped with 1 and 10% Pr3+ were grown by spontaneous nucleation from a K2Mo3O10 and B2O3 flux. Polarised absorption and luminescence spectra in the visible, near infrared and infrared ranges were recorded at room and low temperatures on ground and polished samples of about 1 mm thickness. The microsymmetry of the Pr3+ sites is D3. The observed transitions were assigned and analysed on the basis of the selection rules for the D3 point group. A set of free ion and crystal field parameters in reasonable agreement with the observed energy level structure is reported. The possible applications of the material in the field of optical devices are considered.

Aluminum↗
PubMedDate not supplied

Computerized patient contours using the scanning arm of compound B-scanner.

Full utilization of the precision of newer radiation therapy devices requires patient contours drawn with greater accuracy than is possible with the conventional lead wire technique. Polaroid photographs can introduce large errors due to distortion and small image size. Techniques including electromechanical or optical devices and CT scans offer improved accuracy, but often at added expense. A method for obtaining contours has been developed which utilizes a treatment planning minicomputer (equipped with an analog-to-digital converter and plotter) and a commercially available ultrasound B-scanning arm. Voltages corresponding to the X-Y position of the tip of the scanning arm are fed from the scanner to the A/D interface, smoothed, scaled, and plotted. The resulting drawing is a full scale external patient contour. The accuracy of this method is compared to alternative techniques.

Analog-Digital Conversion↗
PubMed2006

Steady-state directional diffuse reflectance and fluorescence of human skin.

We present numerical simulations predicting the directional diffuse reflectance and autofluorescence from human skin. Skin is modeled as a seven-layered medium, with each layer having its own optical properties and fluorophore concentrations. Both collimated and diffuse monochromatic excitation at 442 nm are considered. In addition, the effect of an index-matching cream used to eliminate total internal reflection within the skin is assessed. We compute the intensity distributions of the excitation and fluorescence light in the skin by solving the radiative transfer equation using the modified method of characteristics. It was found that the use of an index-matching cream reduces the directional fluorescence signal while increasing the directional diffuse reflectance from the skin for collimated excitation. On the other hand, both the fluorescence and diffuse reflectance increase for diffuse excitation with an index-matching cream. Moreover, the directional fluorescence intensity obtained by use of collimated excitation is larger than that obtained by use of diffuse excitation light. This computational tool could be valuable in designing optical devices for biomedical applications.

Algorithms↗
PubMed1993

Intraoperative raster photogrammetry--the PAR Corneal Topography System.

The PAR Corneal Topography System (CTS) is a computer-driven corneal imaging system that uses close-range raster photogrammetry to measure and produce a topographic map of the corneal surface. The CTS determines distortion in a projected two-dimensional grid. Unlike Placido-disc-based videokeratoscopes, the PAR CTS produces a true topographic map (elevation map) and requires neither a smooth reflective surface nor precise spatial alignment for accurate imaging. Because the system uses two noncoaxial optical paths, it can be integrated into other optical devices. A modified CTS was integrated into an experimental erbium: YAG photoablative laser. The CTS successfully imaged corneas before, after, and during laser photoablation. Its ability to image nonreflective surfaces and to be integrated into other optical systems may make it suitable for intraoperative refractive monitoring.

Animals↗