Abstract
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.
Highlights
Due to its fingerprinting characteristics, Raman spectroscopy is well suited for the investigation of biological material, for example, for rapid and nondestructive identification purposes
This paper presents shifted excitation Raman difference spectroscopy (SERDS) investigations using microsystem diode lasers with two slightly shifted emission lines at 783 nm, 671 nm, and 488 nm as excitation light sources
Measurement head for near-infrared excitation, an in-house developed and tested Raman optical bench [9] was combined with a 783 nm distributed feedback (DFB) diode laser [10, 11]
Summary
Due to its fingerprinting characteristics, Raman spectroscopy is well suited for the investigation of biological material, for example, for rapid and nondestructive identification purposes. A reconstruction by means of suitable algorithms, for example, using integration, produces a basically background-free SERDS spectrum revealing weak Raman bands previously masked by fluorescence. This has been demonstrated in the NIR spectral region by da Silva Martins et al [8] applying a mechanically tunable laser in Littrow configuration for the investigation of human skin and tooth. Microsystem diode lasers with target-specific adjustable spectral properties according to the measurement task are well suited Their low power consumption as well as their compact size enables integration into portable systems suitable for SERDS application. To test the performance of the SERDS technique, we chose meat, fat tissue, connective tissue, and bones from pork and beef as sample material to realize a variety of optical properties and fluorescence background levels
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