Single particles, Raman spectroscopy

In this paper, we report on simultaneous consideration of incident field enhancement and local density of photon states enhancement near a metal particle with spherical shape as a reasonable primary model for single molecule Raman spectroscopy. Joint action of these two factors at the same point of space is found to offer up to lO -fold enhancement of Raman scattering rate. To the best of our knowledge this is the first evidence that consistent theory of single molecule Raman spectroscopy and comprehensive description of so-called hot points in surface enhanced spectroscopies can be constructed without necessarily involvement of chemical mechanisms. 

Schrader, B., Micro Raman, Fluorescence, and Scattering Spectroscopy of Single Particles, in Physical and Chemical Characterization of Individual Airborne Particles (K. R. Spurny, Ed.), Chap. 19, pp. 358-379, Ellis Horwood, Chichester, 1986. 

Beside the identification of single bacterial cell or spores by means of Raman spectroscopy, the localization of these cells inside partly complex matrices has to be performed. One approach is the combination of Raman spectroscopy, fluorescence spectroscopy and digital imaging techniques. This method was applied to detect traces of endospores and other biothreat organisms even in the presence of complex environmental matrices like bioaeroso-lic background, nasal mucin [67], or tap water [68], Another fully automated device was built to analyze bioaerosols in clean room environments, where prior to the Raman identification method a particle preselection took place [69]. 

Delhaye and Dhamelincourt (1975) were the first to combine a Raman spectrometer with a microscope. Kiefer (1988) described the Raman spectroscopy of single particles of aerosols by the optical levitation technique, an approach which is even possible with a compact spectrometer (Hoffmann et al., 1992). Raman spectra recorded with NIR FT Raman microscopes have proven the value of this technique (Messerschmidt and Chase, 1989 Bergin and Shurwell, 1989 Simon and Sawatzki, 1991). Examples of micro Raman spectra obtained from different spots on certain biological samples have been published (Schrader, 1990 Puppels et al., 1991). 

Ajito K, Torimitsu K (2001) Near-infrared Raman spectroscopy of single particles. Trac-Trends Anal Chem 20(5) 255-262... 

Conductivity can be deduced from vibrational spectra in IR spectroscopy, the absorption coefficient a(co) is related to tr(co) a(o)) = 4no(o))/nc, n being the refractive index and c the velocity of light. In Raman spectroscopy, the scattered intensity /(m) is related to conductivity by a(o ) oc o)I (o)/n(a)) + 1, n(co) being the Bose-Einstein population factor . Finally, the inelastic incoherent neutron scattering function P(o)) is proportional to the Fourier transform of the current correlation function of the mobile ions. P co) is homogeneous with a) /(cu) formalism. However, since P(co) reflects mainly single particle motions, its comparison with ff(co) could provide a method for the evaluation of correlation effects. (For further discussion, see also Chapter 9 and p. 333.)... 

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