Noninvasive Detection of Skin Moisture Content Based on Spatially Offset Raman Spectroscopy

In this study, the feasibility of detecting skin water content based on spatial displacement Raman spectroscopy and portable fiber optic spectrometer was explored. A device was constructed that can achieve an optimal spatial displacement distance of 300 mu m. It is selected to detect signals noninvasively under the surface of the skin and reduce the interference of pollutants such as water and oil on the surface of the skin. Instead of using the traditional spatial shift Raman spectroscopy device to achieve the relative shift of excitation point and collection point by mechanical offset or light blocking, a micro-shiftable light source was set up to adjust the spatial shift by using the conjugate relationship between the light source and the excitation point, and at the same time, a microscopic imaging device was introduced to control the adjustment, which finally realized the continuous adjustable spatial shift of less than 1 000 mu m. The ratio of the intensity of Raman shift at 3 390 cm(-1) (water Raman peak) and 2 935 cm(-1) (protein Raman peak) is employed to characterize the skin moisture content, a portable spectrometer is employed to make the device moveable, the probe and the spectrometer are connected by optical fiber to make the probe flexible. Therefore, the design meets the clinical requirements. In total, 70 spectra from different locations were collected (7 people, 10 spectra each) in the experiment, and the spectra were processed by a de-backgrounding algorithm, and then the exact Raman peak intensity was obtained. The intra-group correlation coefficient was used as an index for consistency analysis. The intra-group correlation coefficient of 0.889 for a single measurement showed that the results of the two methods were in good agreement. In this study, four experiments with different spatial displacement amounts were set up, and the spatial displacement distances were 200 mu m, 300 mu m, 500 mu m and 1 000 mu m. The skin spectra from the same person at the same location measured under different spatial displacement amounts can be seen to be significantly different only in signal intensity, while there is no significant and regular change in the spectral profile and details, and it is impossible to distinguish which spectrum is better The results of the quantitative analysis can only be judged by the results of the quantitative analysis. The experimental and analytical procedures described above were repeated at four spatial shifts in the study, and it was finally confirmed that the best results could be obtained at a spatial shift of 300 mu m. After proving the spatial sensitivity of the device by statistical methods and obtaining the optimal device parameters, we also hope to conclude a more intuitive method to quickly judge the signal superiority by spectral characteristics. As the spatial displacement distance increases, the spectral height decreases in turn, but the consistency shows a trend of first increasing, then decreasing and then increasing with the decreasing spectral height, there is no rule, so we cannot judge the signal superiority from the spectral height. We note that even for the same person at the same location, the relative intensity of the water signal (the ratio of the intensity of the Raman shift at 3 390 cm(-1) and 2 935 cm(-1)) is not equal under the detection conditions of different spatial shift distances, the reason is that not all depths of the skin can correctly reflect the water content. Overall, if the relative intensity of the water signal is less than 0.05, then the detection results will only have low confidence, for example, when the spatial displacement distance is 500 mu m in the experiment, the relative intensity of the water signal is only 0.023, and the intra-group correlation coefficient is only 0.316. Under such conditions, it is necessary to adjust the optical path or check whether the skin of the subject has damage, scars and other problems; if the relative intensity of the water signal is close to 0.10, you can judge that the optical path configuration at this time is basically qualified, only need further fine tuning to determine the best parameters, the empirical method can quickly and effectively filter the weak signal, strong background spectrum, improve the efficiency of the study. It is proved that the experimental device can obtain a spectrum with good repeatability. The design of the fiber spectrometer and probe separation also meets the practical requirements, which is convenient for a large number of human body measurement experiments and has the potential to be transformed into medical devices. Indicating that the skin water content measured based on the spatial displacement Raman spectroscopy has high effectiveness and is expected to achieve convenient detection of the skin inner water content.