Optical techniques in biology

Spectroscopic measurements have been very valuable in the investigation of biological systems. They have led to much important information about structure they have been invaluable in the identification of substances and they are used routinely for the measurement of concentrations of known substances. 

Aside from purely spectroscopic techniques, other optical methods have been employed to study substances of interest to biologists. Examples are the study of optical rotation and of optical rotatory dispersion. These latter types of investigation will be considered in the next chapter with special application to biological problems. 

We have seen that, in the infrared region of the spectrum, there are spectral bands associated with both vibrational and rotational transitions. Pure rotational transitions are found in the microwave region of the spectrum, which is beyond the infrared, but studies of these are not of great value in the investigation of large molecules. Studies of the vibrational-rotational spectra in the infrared have, however, made very important contributions to biological research. 

Measurements in the infrared therefore must be made with the substance present in a material that does not absorb. Certain organic solvents are used frequently for this purpose. Alternatively, the solvent is eliminated completely. A common modern technique is to disperse the sample in a suitable inorganic salt, usually potassium bromide. The sample is mixed with the powdered crystalline salt, which is then pressed into a transparent disk measuring 0.5 mm in thickness and 10 mm in diameter. The disk is then mounted in a holder which is supported in the beam of the infrared instrument. There are some experimental difficulties which can be overcome by a skillful investigator. Since aqueous systems cannot be used in such experiments, infrared spectroscopy has no direct value in the study of biological systems, which are always aqueous. The usefulness of spectroscopy to the biologist is in the study of substances that have been extracted from biological systems. 

Besides the usefulness of infrared spectra in the identification of individual bonds, the technique is of great value in leading to an absolute identification of a pure compound. Because of the large numbers of vibrational modes in a molecule, the complete infrared spectrum of a given molecule will be very complicated and quite 

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Palumbo G, Pratesi R. Laser and Current Optical Techniques in Biology. Cambridge Royal Society of Chemistry, 2004. 

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H. Schneckenburger, Optical Microscopy, in Lasers and Current Optical Techniques in Biology (G. Palumbo, R. Pratesi, eds.). Comprehensive Series in Photochemistry and Photobiology, Vol. 5, Royal Society of Chemistry, Cambridge, U.K., 2004, pp. 331-355. 

Katzir, A. (1997). Lasers and Optical Fibers in Medicine (Physical Techniques in Biology and Medicine), Academic Press, San Diego. 

Marchese-Ragona, S. P. and P. G. Haydon (1997). "Near-field scanning optical microscopy and near-field confocal optical spectroscopy Emerging techniques in biology." Ann N YAcad Sci 820 196-206 discussion 206-7. 

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Koroteev N I 1995 BioOARS—a novel nonlinear optical technique to study vibrational spectra of chiral biological molecules in solution Biospectroscopy 1 341-50... 

There is the microtoming optical analysis test. In this procedure thin slices (under 30 tixri) of the plastics are cut from the product at any level and microscopically examined under polarized light transmitted through the sample. Rapid quality and failure analysis examination occurs by this technique. This technique has been used for many years in biological studies and by metallurgists to determine flaws, physical and mechanical properties. Examination can be related to stress patterns, mechanical properties, etc. 

Liquid interfaces are widely found in nature as a substrate for chemical reactions. This is rather obvious in biology, but even in the diluted stratospheric conditions, many reactions occur at interfaces like the surface of ice crystallites. The number of techniques available to carry out these studies is, however, limited and this is particularly true in optics, since linear optical methods do not possess the ultimate molecular resolution. This resolution is inherent to nonlinear optical processes of even order. For liquid-liquid systems, optics turns out to be rather powerful owing to the possibility of nondestructive y investigating buried interfaces. Furthermore, it appears that planar interfaces are not the only config-... 

Luminescence, in particular photoluminescence, constitutes a well-established discipline in analytical science where the cited hallmarks include remarkable sensitivity, wide dynamic range and low detection limits (-10under suitable conditions). These collective merits are often umivaled by other optical techniques, and hence its wide adoption in the life sciences for determining trace constituents in biological and environmental samples. Moreover, its fast response, high spatial resolution and remote sensing capabilities make it attractive for real-time analytical problems such as process manufacturing (process analysis or PAT) and field applications. ... 

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