Scanning near-field fluorescence resonance energy transfer microscopy.
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A new microscopic technique is demonstrated that combines attributes from both near-field scanning optical microscopy (NSOM) and fluorescence resonance energy transfer (FRET). The method relies on attaching the acceptor dye of a FRET pair to the end of a near-field fiber optic probe. Light exiting the NSOM probe, which is nonresonant with the acceptor dye, excites the donor dye introduced into a sample. As the tip approaches the sample containing the donor dye, energy transfer from the excited donor to the tip-bound acceptor produces a red-shifted fluorescence. By monitoring this red-shifted acceptor emission, a dramatic reduction in the sample volume probed by the uncoated NSOM tip is observed. This technique is demonstrated by imaging the fluorescence from a multilayer film created using the Langmuir-Blodgett (LB) technique. The film consists of L-alpha-dipalmitoylphosphatidylcholine (DPPC) monolayers containing the donor dye, fluorescein, separated by a spacer group of three arachidic acid layers. A DPPC monolayer containing the acceptor dye, rhodamine, was also transferred onto an NSOM tip using the LB technique. Using this modified probe, fluorescence images of the multilayer film reveal distinct differences between images collected monitoring either the donor or acceptor emission. The latter results from energy transfer from the sample to the NSOM probe. This method is shown to provide enhanced depth sensitivity in fluorescence measurements, which may be particularly informative in studies on thick specimens such as cells. The technique also provides a mechanism for obtaining high spatial resolution without the need for a metal coating around the NSOM probe and should work equally well with nonwaveguide probes such as atomic force microscopy tips. This may lead to dramatically improved spatial resolution in fluorescence imaging. (+info)
"Uncaging" using optical fibers to deliver UV light directly to the sample.
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Photolysis or "uncaging" of caged compounds represents a significant tool in cell biology and chemistry. It provides a means for quantitative control of compound delivery with temporal and spatial resolution while observing their consequences for cellular signaling. We discuss the use of ultraviolet-transmitting optical fibers to directly deliver UV energy to the sample, combined with a nitrogen pulsed laser as a source of UV light. In this approach the size of the photolysis area is regulated by the exit aperture of the fiber tip which is controlled by pulling the optical fibers to desirable diameters. A diode (red) laser that is also coupled to the optical fiber aids the location of UV energy delivery through the fiber. We used this method to quantitatively uncage norepinephrine and calcium. The major advantage of this photolysis approach is its independence of microscope objectives and traditional optical pathways. Because the optical pathway of the microscope needs no modification to accommodate this photolysis system, integration with other experimental methods, such as electrochemistry, electrophysiology, confocal microscopy, and wide-field epifluorescence microscopy, is relatively simple. (+info)
Clinical assessment of a plastic optical fiber stylet for human tracheal intubation.
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BACKGROUND: The authors compared the performance of a prototype intubation aid that incorporated plastic illumination and image guides into a stylet with fiberoptic bronchoscopy and direct laryngoscopy for tracheal intubation by novice users. METHODS: In a randomized, nonblinded design, patients were assigned to direct laryngoscopy, fiberoptic bronchoscopy, or imaging stylet intubation groups. The quality of laryngeal view and ease with which it was attained for each intubation was graded by the laryngoscopist. Time to intubation was measured in 1-min increments. A sore-throat severity grade was obtained after operation. RESULTS: There were no differences in demographic, physical examination, or surgical course characteristics among the groups. The laryngoscope produced an adequate laryngeal view more easily than did the imaging stylet or bronchoscope (P = 0.001) but caused the highest incidence of postoperative sore throat (P<0.05). Although the time to intubation for direct laryngoscopy was shorter than for imaging stylet, which was shorter than fiberoptic bronchoscopy (P<0.05), the quality of laryngeal view with the imaging stylet was inferior to both direct laryngoscopy and fiberoptic bronchoscopy techniques (P<0.05). CONCLUSIONS: Novices using the imaging stylet produce fewer cases of sore throat (compared with direct laryngoscopy) and can intubate faster than when using a bronchoscope in anesthetized adult patients. The imaging stylet may be a useful aid for tracheal intubation, especially for those unable to maintain skills with a bronchoscope. (+info)
A rapid reusable fiber optic biosensor for detecting cocaine metabolites in urine.
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Analyte 2000, a four-channel fiber optic biosensor (FOB), was used for analysis of cocaine and its metabolites (COC) in human urine using a competitive fluorescence immunoassay. Binding of antibenzoylecgonine monoclonal antibody (mAb) to the casein-benzoylecgonine Ag-coated, tapered optical fibers was inhibited by COC. Bound mAb, which inversely correlated with COC concentration, was quantitated by fluorescence produced by evanescent excitation of bound cyanine dye-tagged antimouse antibody (CY5-Ab). The effective concentration range of benzoylecgonine (BE) for inhibiting the fluorescent signals was 0.75-50 ng/mL, with IC50 of 9.0 ng/mL. This FOB had similar affinities for BE, cocaine, and cocaethylene, but very low affinities for ecgonine and ecgonine methyl ester. A sensitivity of 100% and a specificity of 96% were achieved when 54 human urine specimens were analyzed by FOB (cutoff, 300 ng/mL COC) and GC-MS (cutoff, 150 ng/mL BE). All results were in agreement except for one positive FOB result with a GC-MS BE concentration of 148 ng/mL. In addition, regeneration and reuse of the fiber for multiple analyses were performed successfully with no carryover from specimens containing high COC concentrations to specimens containing low COC concentrations. (+info)
Evaluation of porcine fat with fiber-optic spectroscopy.
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Spectroscopy using four types of fiberoptic probes and a sensor at wavelengths of 400 to 1,100 nm was evaluated to assess porcine fat quality. The shapes of the spectrum for the leaf fat with white color and various firmnesses differed with the type of probe: surface, contact, insertion, or transmittance. The internal reflectance ratio using the insertion probe at wavelengths from approximately 600 to 1,000 nm was positively correlated with the hardness, melting point, and saturated fatty acid content of the fat, but it was negatively correlated with the refractive index and polyunsaturated fatty acid content. The correlations between the internal reflectance ratio using the insertion probe and the monounsaturated fatty acid content were strong only near 1,100 nm. Surface reflectance at more than 650 nm was negatively correlated with refractive index. Transmittance at almost all wavelengths showed positive correlations with monounsaturated fatty acid content, but it was negatively correlated with hardness, melting point, and saturated fatty acid content. The interactance using the contact probe did not have a significant correlation with any physiochemical characteristics. The strongest relationships for hardness, refractive index, saturated fatty acid content, monounsaturated fatty acid content, polyunsaturated fatty acid content, and melting point were obtained at 650 nm (r = .88), 660 nm (r = -.91), 645 nm (r = .73), 1,095 nm (r = .68), and 930 nm (r = -.76), respectively, using the insertion probe and 1,050 nm (r = -.79) using the transmittance probe (P<.05). These results indicated that fiber-optic methods were rapid and useful techniques for the evaluation of porcine fat quality. (+info)
Laser desorption in transmission geometry inside a Fourier-transform ion cyclotron resonance mass spectrometer.
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We report here the first application of laser desorption (LD) in transmission geometry (backside irradiation of the sample through a transparent support) inside a Fourier-transform ion cyclotron resonance mass spectrometer (FT-ICR). A probe-mounted fiber optic assembly was used to simplify the implementation of this LD technique. This setup requires little or no instrument modifications, has minimum maintenance requirements, and is relatively inexpensive to build. The performance of the probe was tested by determining the molecular weight of a commercial polystyrene standard from its matrix-assisted laser desorption/ionization (MALDI) spectrum. The measured average molecular weight is comparable to that obtained for the same sample by MALDI in the conventional top-illumination arrangement (reflection geometry) and by the manufacturer of the sample by gel permeation chromatography. The average velocities measured for ions evaporated by transmission mode LD of several neat samples are about half the velocity of those obtained by using the reflection geometry. Therefore, transmission mode irradiation of the sample holds promise to desorb ions that are easier to trap in an ICR cell. An oscillating capillary nebulizer was adapted for the deposition of analytes to improve sampling reproducibility. (+info)
PMD fundamentals: polarization mode dispersion in optical fibers.
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This paper reviews the fundamental concepts and basic theory of polarization mode dispersion (PMD) in optical fibers. It introduces a unified notation and methodology to link the various views and concepts in Jones space and Stokes space. The discussion includes the relation between Jones vectors and Stokes vectors, rotation matrices, the definition and representation of PMD vectors, the laws of infinitesimal rotation, and the rules for PMD vector concatenation. (+info)
Generation of electrospray from a solution predeposited on optical fibers coiled with a platinum wire.
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This study examines the feasibility of generating electrospray directly from the tip of two optical fibers bound together with Teflon tape. This approach does not require a capillary and syringe pump. The electrospray source is simply constructed by coiling the two optical fibers with a platinum (Pt) wire. The optical fibers extend beyond the Pt coil for approximately 1 cm. The sample solution is predeposited on the Pt coil by a micropipette. As the high voltage required for electrospray is applied to the coil, the sample solution moves along the grooves between the two optical fibers. A stable electrospray is subsequently generated at the tip of the fibers. The mass spectra of insulin, lysozyme, and ubiquitin are exactly the same as those obtained by conventional electrospray using a capillary and syringe pump. Rapid determination of the active ingredient in a tablet by this technique is demonstrated. (+info)