Development and applications of highly-sensitive near-infrared multichannel Raman Spectroscopic system

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A highly sensitive near-infrared multichannel Raman spectroscopic system has been constructed. We use the 1064 nm line of a cw Q-switched Nd : YAG laser for excitation and a new InP/InGaAsP intensified CCD detector for detection. The system has a detectivity at least one order of magnitude higher than the conventional FT-Raman spectrometer and is capable of recording high S/N Raman spectra without the interference from fluorescence. 1) We are now able to measure the Raman spectra of human lung tissues, by virtue of fluorescence-free near-infrared excitation. We have found that the Raman spectra of cancered lung tissues are quite different from those of normal lung tissues. This result indicates that Raman spectroscopy distinguishes cancered and normal tissues very clearly and that it has a huge potential for in vivo and non-invasive clinical diagnosis of cancers. An optical-fiber irradiation/collection optics has been developed in order to facilitate in vivo Raman measurements. 2) Time- and space-resolved Raman spectra of a living yeast cell have been observed for the first time, using a confocal Raman microspectroscopic system with 632.8 nm excitation. Time- and space-dependent Raman bands of proteins, lipids, and sugars are observed, reflecting the evolution with the cell cycle of the molecular compositions in organelles like nucleus, mitochondrion and septum. 3) The near-infrared Raman system has been applied for the measurements of various protein and nucleic acid samples. Despite the fact that those samples fluoresce strongly with visible excitation, no interference from fluorescence has been observed with 1064 nm excitation. Structural change of DNA with drug intercalation has successfully been probed. In conclusion, the present research has established the methodology of near-infrared Raman spectroscopy, which is particularly useful in biomedical applications.