Fiber-optic light guides

Surface fluorescence of NADH/NADPH can be recorded continuously with a DC fluorimeter and correlated with changes in experimental conditions. A mercury arc lamp (with a 340-375 nm filter in front) is used as a hght source for fluorescence excitation. The fluorescence response of reduced NADH/NADPH was measured at 450-510 nm. The DC fluorimeter and the Hg arc lamp are connected to the kidney by a trifurcated fiber optics light guide. NADH/NADPH fluorescence emission can be corrected for changes in tissue opacity by a 1 1 subtraction of reflectance changes at 340-375 nm from the fluorescence. To determine NADH/NADPH redox state of the total surface area of kidney cortex and to evaluate whether certain areas were insufficiently perfused, fluorescence photographs of the total surface area were taken. The study demonstrated that the surface fluorescence method is simple and provides specific information about the mitochondrial oxidation-reduction state. 

The light transmission technique is most frequently used for the determination of average bubble size in gas-liquid dispersion. It has the advantages of quick measurement and on-line operation. The probes are usually made of mirror-treated glass rods (Vermeulen et al., 1955), internally blackened tubes with mirrors (Calderbank, 1958), or fiber optic light guide (Hong and Lee, 1983). 

A heat-absorbing lens should be attached to the end of each fiber optic light guide to reduce the desiccation of exposed tissue, and in particular the uterine swellings,... 

FIGURE 37.29 Attenuation of typical fiber-optic light guides. 

Besides cell designs that employ metals or other electrode materials in disc shape for external reflection spectroscopy, Robinson and McCreery have successfully employed cylindrical carbon fibers of 12 pm diameter [58, 59]. The carbon fiber was illuminated with a tunable dye laser. Scattered light was collected with fiber optics and guided to a photomultiplier detector. Because no thin layer arrangement and consequently poor electrochemical cell response were involved, fast experiments on a microsecond time scale were possible. Studies of polyaniline films deposited on platinum discs have been described [60]. 

Some of the CCDs mentioned above are a few millimeters in diameter. Such a CCD could be placed at the distal end of an endoscope and used for imaging, instead of the ordered bundle of optical fibers. A light guide is still used in these endoscopes for illumination. Such endoscopes can provide imaging at a video rate from internal organs and they are called videoscopes. It is estimated that roughly 50% of the flexible endoscopes used today are videoscopes. These endoscopes are still relatively thick and they are mostly used in gastroscopy and colonoscopy. 

Another early fiber optic refractive "sensor" was the one for measurement of temperature and salinity variations of sea water31. The sensing region consisted of a partly uncovered light guide. It detects salinity variations in water of known temperature, and temperature variations in water of known salinity with an accuracy of +/- 2 g/L and 1 °C, respectively, at NaCl concentrations of 300 g/L. 

Kopelman et al.73 have prepared fiber optic sensors that are selective for nitric oxide and do not respond to most potential interferents. Both micro-and nanosensors have been prepared, and their response is fast (<1 s), reversible, and linear up to 1 mM concentrations of nitric oxide. The respective "chemistry" at the fiber tip was contacted with the sample, light was guided to the sample through the microfiber, and emitted light was collected by a microscope (without the use of fibers, however). 

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