Raman spectroscopy biological samples

The use of an Intense laser light source with biological materials Is accompanied by the concomitant problems of localized sample heating and the possibility of protein denaturetlon. A further complication Introduced by resonance Raman spectroscopy Is the Increased potential for photochemical destruction of chromo-phorlc metal centers as a result of the absorption of large amounts of Incident radiation. Both of these situations may be ameliorated by freezing samples to liquid nitrogen temperature ( 90 K), while the even lower temperatures made possible with a closed-cycle... 

One further attraction of the Raman technique for vibrational studies is that water of bonded OH groups does not cause obscuration of the spectrum but, of course, Raman spectroscopy is useless for studies on water in polymers. At Southampton, excellent spectra of numerous solid mono-, di-, and trisaccharides have been recorded as well as aqueous solutions of some species. It is quite probable that Raman spectra of biologically interesting polymers may be produced shortly8. The ability to examine samples in aqueous regimes obviously has its attractions to the biochemist 1... 

The possibility of obtaining information about lipid-protein interaction makes Raman spectroscopy a useful technique for structural studies of membranes. As an illustration of spectra recorded from biological samples, see the Raman spectrum of a frog sciatic nerve in Figure 11. The C-H stretching vibration region is characteristic of lipid bilayers in a... 

A series of advances over the past decade have made CRS microscopy a highly sensitive tool for label-free imaging and vibrational microspectroscopy that is capable of real-time, non-perturbative studies of complex biological samples based on molecular Raman spectroscopy. In particular, biomedical applications where fluorescent labeling of small molecules represents a severe pertur-... 

Uniform analyte distribution is often a good assumption for liquid samples such as blood serum or even whole blood if stirring is continuous. For biological tissue, human skin in particular, heterogeneity is a major factor. Detailed morphological structures and molecular constituents of skin have been studied using confocal Raman spectroscopy.9... 

A limiting factor in noninvasive optical technology is variations in the optical properties of samples under investigation that result in spectral distortions44 8 and sampling volume (effective optical path length) variability 49-54 These variations will impact a noninvasive optical technique not only in interpretation of spectral features, but also in the construction and application of a multivariate calibration model if such variations are not accounted for. As a result, correction methods need to be developed and applied before further quantitative analysis. For Raman spectroscopy, relatively few correction methods appear in the literature, and most of them are not readily applicable to biological tissue.55-59... 

Raman spectroscopy can be used to analyse aqueous biological and bio-organic samples e.g., bacteria, spores, diseased tissues, neurotransmitters,... 

Since water is a weak Raman scatterer, Raman spectra of samples in aqueous solution can be obtained without major interference from water vibrations. Thus, Raman spectroscopy is ideal for the studies of biological compounds in aqueous solution. In contrast, IR spectroscopy suffers from the strong absorption of water. 

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). 

These results show that Raman spectroscopy may be used to quantify the thermodynamic properties of molecules with at least the same accuracy as IR spectroscopy. However, the main advantage of Raman spectroscopy lies in the possibility of determining the sample temperature of precisely those molecules which are excited by the laser beam from Stokes/anti-Stokes intensity ratios. Furthermore, investigations of aqueous solutions (such as biological samples) are expected to create less technical problems than IR window materials. 

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