Water is critical for skin to function normally as a barrier to prevent moisture and heat loss from a body. Raman spectroscopy has high potential in skin hydration analysis as the measurement requires no contacts with the skin. However, traditional CCD based Raman spectrometer has limited performance in detecting high energy vibrations including CH and OH groups. This work reports a customized InGaAs based Raman spectrometer for probing high energy vibration bands. Chicken and pork skin samples were analyzed, and their Raman spectra were compared to other tissues such as fat, tendon, and muscle to determine the spectroscopic identities of CH and OH groups. These results indicate that water components are mostly unbounded in skin tissues. The results further suggest that muscle and tendon components are beneficial for storing water in skin tissue and possibly preventing skin dehydration.
Precise information on dispersion of the nonlinear optical susceptibility of Raman active media is essential in order to get an insight into physics and chemistry of intra- and inter-molecular interactions. We propose and experimentally demonstrate a method that is capable of resolving both real and imaginary parts of third-order nonlinearity (χ(3)) in the vicinity of Raman resonances. Dispersion of χ(3) can be obtained from a medium probed within microscopic volumes with a spectral resolution of better than 0.1 cm-1 thus making our approach an essential tool in quantitative microscopic characterization of complex biological media. Time-domain CARS transients traced with femtosecond pulses within orders of magnitude in the signal decay can lead to resolution of fine spectral features in χ(3) dispersion that can not be reliably detected by frequency-domain Raman based spectroscopy/microscopy techniques, including coherent methods. We will present results of the method’s application in biological cells and tissue. Namely, we accessed a protein line at 1245 cm-1 in E-coli cell, major DNA and protein lines in red blood cells and triglyceride Raman active peaks in fat tissue.
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