%0 Journal Article
%T Fluorescence Rejection by Shifted Excitation Raman Difference Spectroscopy at Multiple Wavelengths for the Investigation of Biological Samples
%A Kay Sowoidnich
%A Heinz-Detlef Kronfeldt
%J ISRN Spectroscopy
%D 2012
%R 10.5402/2012/256326
%X Shifted excitation Raman difference spectroscopy (SERDS) was applied for an effective fluorescence removal in the Raman spectra of meat, fat, connective tissue, and bone from pork and beef. As excitation light sources, microsystem diode lasers emitting at 783£¿nm, 671£¿nm, and 488£¿nm each incorporating two slightly shifted excitation wavelengths with a spectral difference of about 10£¿cm£¿1 necessary for SERDS operation were used. The moderate fluorescence interference for 783£¿nm excitation as well as the increased background level at 671£¿nm was efficiently rejected using SERDS resulting in a straight horizontal baseline. This allows for identification of all characteristic Raman signals including weak bands which are clearly visible and overlapping signals that are resolved in the SERDS spectra. At 488£¿nm excitation, the spectra contain an overwhelming fluorescence interference masking nearly all Raman signals of the probed tissue samples. However, the essentially background-free SERDS spectra enable determining the majority of characteristic Raman bands of the samples under investigation. Furthermore, 488£¿nm excitation reveals prominent carotenoid signals enhanced due to resonance Raman scattering which are present in the beef samples but absent in pork tissue enabling a rapid meat species differentiation. 1. Introduction Due to its fingerprinting characteristics, Raman spectroscopy is well suited for the investigation of biological material, for example, for rapid and nondestructive identification purposes. Here, excitation wavelengths in the visible or near-infrared range are preferable to avoid strong absorption of water leading to sample heating [1]. For that reason, in situ Raman investigations are possible since no sample pretreatments, as for example, drying procedures, are necessary. According to the ¦Ë£¿4-dependence of the Raman scattering intensity, the application of shorter excitation wavelengths can significantly improve the spectral quality. On the other hand, this leads to an increased fluorescence interference partly or completely obscuring the Raman signals and thus making the detection of useful spectra hardly possible. There exist certain methods to remove the fluorescence background from the Raman spectra to overcome the fluorescence issue. In that way, mathematical approaches as polynomial [2] or advanced subtraction methods [3] as well as experimental techniques using a temporal discrimination of the slower fluorescence emission against the Raman photons [4, 5] were successfully applied. As a technique additionally removing the
%U http://www.hindawi.com/journals/isrn.spectroscopy/2012/256326/