Resonance Raman spectroscopy
Whereas conventional Raman spectroscopy measures light scattered weakly by molecular vibrations and independent of the excitation wavelength, resonance Raman spectroscopy measures molecular vibration in a wavelength-dependent manner, strongly enhanced by using an excitation wavelength close to an electronic transition. The resonance version is much more sensitive and selective because of the wavelength dependence. With surface enhancement, resonance Raman spectroscopy can achieve single-molecule sensitivity.
Researchers from Laser Centre Vrije Universiteit Amsterdam in the Netherlands have reviewed decades of developments in resonance Raman spectroscopy and contend that these advancements have made it possible for the technique to become a widely used tool for biochemical analysis.
In some promising cases, it has been performed successfully at visible wavelengths using standard continuous-wave krypton and argon lasers, although performing it in the visible range remains challenging because of fluorescence interference. Many of the advancements have concerned overcoming these background fluorescence signals. For example, recently developed instruments operate at deep-UV wavelengths that do not evoke fluorescence signals. Alternatively, time-resolved resonance Raman spectroscopy using pulsed lasers and fast-gated detectors has been used to reject fluorescence signals.
Several other technological advancements have occurred. The emergence of fiber-coupled instruments has simplified alignment and sampling requirements and has enabled the technique to probe hard-to-reach areas. The method also has been combined with liquid chromatography and capillary electrophoresis to yield promising results. User-friendly mathematical modeling software is becoming available to predict resonance enhancement factors as a function of excitation wavelength and the symmetry of the vibration.
The authors provide examples of biological applications of the technique, including studies of nucleic acids, proteins, metalloproteins, drug-protein interactions, carotenoids and heme-protein complexes. For instance, the technique was used to determine the relative amounts of DNA bases in bacteria, and this information enabled prediction of bacterial genus and culture conditions. (Analytica Chimica Acta, Jan. 14, 2008, pp. 119-134.)
- raman spectroscopy
- That branch of spectroscopy concerned with Raman spectra and used to provide a means of studying pure rotational, pure vibrational and rotation-vibration energy changes in the ground level of molecules. Raman spectroscopy is dependent on the collision of incident light quanta with the molecule, inducing the molecule to undergo the change.
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