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Device for Raman difference spectroscopy.

A new layout of a versatile Raman difference setup is presented. The new device combines the advantages of the rotating cell for exploitation of the resonance Raman enhancement and the high precision of Raman difference spectroscopy together with the multiplex advantages and very high quantum efficiency offered by a CCD detector. While Raman difference spectroscopy is the most accurate method for the detection of very small band shifts, the method requires the strict prevention of any environmental perturbation of one of the two spectra, which are used for the difference spectra calculation. The presented device satisfies this requirement by implementing a double-beam layout, where the simultaneously detected Raman signals of two sample cells are combined within a Y-fiber bundle and imaged together onto the CCD detector. The accuracy of the new apparatus in detecting frequency shifts and minor sample components is greatly increased compared to conventional Raman spectroscopy as shown by studying binary mixtures of CHCl3 and CCl4. Hereby it was possible to resolve a formerly undetected shift of <0.02 cm(-1) of the CCl4 band at 218 cm(-1). The new RDS setup has a very versatile design. The device can take advantage of the high sensitivity and selectivity of the resonance Raman enhancement applying excitation wavelengths from the UV to NIR and can be used for a variety of samples with only minor changes in the optical arrangement. The new device will be of utmost importance for a fast, gentle, sensitive, selective, and precise investigation of biomolecules and their interactions. Some first results are shown concerning the interaction of the antimalarial chloroquine with hematin in a hydrous environment.