Fiber bundles, bifurcated

Figure 14 14. Biocatalytic optodes based on a bifurcated fiber bundle (top) or a single fiber (bottom). In the recognition part the indicator and an enzyme are immobilized. The reactive layer is permeable to the substrate but protected against light.

Fiber optics may be used as probes for conventional spectrophotometric and fluorescence measurements. Light must be transmitted from a radiation source to the sample and back to the spectrometer. While there are couplers and designs that allow light to be both transmitted and received by a single fiber, usually a bifurcated fiber cable is used. This consists of two fibers in one casing, split at the end that goes to the radiation source and the spectrometer. Often, the cables consist of a bundle of several dozen small fibers, and half are randomly separated from the other at one end. For absorbance measurements, a small mirror is mounted (attached to the cable) a few millimeters from the end of the fiber. The source radiation penetrates the sample solution and is reflected back to the fiber for collection and transmission to the spectrometer. The radiation path length is twice the distance between the fiber and the mirror. 

A model 6500 On-Line Vis-NIR spectrophotometer (NIR Systems, Inc., Silver Spring, MD) equipped with single bundle bifurcated fiber optics was used for data acquisition. An Interactance Reflectance probe was used along with a novel extruder/monitor interface design to obtain diffuse reflectance spectra of the plastic melt near the die. The visible region of the spectrum (400-700 nm) was used for analysis. Figure 2 shows a schematic of the experimental setup. 

Apparatus. The fiber optic photometer is similar to the instrument used in earlier work (2). It includes a tungsten-halogen source, a photomultiplier detector, interference filters for wavelength selection and a bifurcated fiber optic bundle 3 mm in diameter at the common end. In this study, excitation filters had peak transmittances at 420 and 480 nm and the emission filter had peak transmittance at 520 nm. The bandwiths at half-maximum transmittance were 9.4, 8.2 and 8.6 nm for the 420, 480 and 520 nm filters, respectively. An automated filter wheel allowed for rapid switching from one filter to another. 

The first step in preparing a sensor is to dissolve 100 mg of PVOH/indicator conjugate in 2.0 mL of water. Five minutes in a water bath at 30°C is required to get the PVOH to dissolve. After cooling to room temperature, 0.5 mL of PVOH/indicator solution is combined with 0.050 mLs each of 2% aqueous glutaraldehyde and 4 M HCl. This mixture can be manipulated as a liquid for about five, minutes until sufficient crnsslinking takes place to cause the solution to gel. During this interval a micropipet is used to precisely transfer 3 microliters to the common end of the bifurcated fiber optic bundle so that the gel forms in situ. 

This reaction produces p-nitrophenoxide which strongly absorbs 404 nm radiation. The sensor tip is constructed with alkaline phosphatase covalently immobilized on a nylon membrane. This membrane is positioned at the common end of a bifurcated fiber-optic bundle. One arm of this bundle is connected to the source optics and the other is connected to the detector optics. Incident radiation is transported from a 100 watt tungsten-halogen lamp source to the sensor tip. A fraction of this incident radiation is back scattered off the nylon mesh and a fraction of this back scattered radiation is collected by the fiber-optic bundle and directed to a 404.7 nm interference filter and then to a photomultiplier tube detector. 

FIGURE 5 Design principle of fiber-optic chemical sensors, (a) Two single fibers, (b) Two fiber bundles, (c) Bifurcated fiber. 

The fiberoptic spectrophotometer was composed of a bifurcated fiber optic (common leg bundle diameter 4.5 mm, individual leg bundle diameter 2.5 mm) and a fluoropho-tometer with a data recorder. Two arms of the bifurcated fiberoptic bundle were fixed between the excitation monochromator and the emission monochromator. 

Figure 15.23. Infrared fiber bundle coupled to a firustiated total reflection IRE. The fiber bundle is bifurcated so that input and output radiation can be separated- (Courtesy of Remspec Corporation.)...

Abstract Identification of the anatomical anterior cruciate ligament (ACL) footprint is essential in femoral tuimel preparation. The lateral intercondylar ridge (LIR), which is termed the anterior border of the femoral ACL footprint, can be used as a landmark during surgery. The entire ACL footprint consists of the direct insertion of the ACL located behind the LIR and the attachment of fanlike extension fibers extended to the posterior cartilage margin. The lateral bifurcate ridge can be observed between the attached anteromedial (AM) and posterolateral (PL) bundles in 80 % of cases. 

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