Visualization of epidermal cells is important because the differentiation patterns of keratinocytes (KCs) are considered to be related to the functions and condition of skin. Optical microscopy has been widely used to investigate epidermal cells, but its applicability is still limited because of the need for sample fixation and staining. Here, we report our staining-free observation of epidermal cells in both tissue and culture by stimulated Raman scattering (SRS) microscopy that provides molecular vibrational contrast. SRS allowed us to observe a variety of cellular morphologies in skin tissue, including ladder-like structures in the spinous layer, enucleation of KCs in the granular layer, and three-dimensional cell column structures in the stratum corneum. We noticed that some cells in the spinous layer had a brighter signal in the cytoplasm than KCs. To examine the relevance of the observation of epidermal layers, we also observed cultured epidermal cells, including KCs at various differentiation stages, melanocytes, and Langerhans cell-like cells. Their SRS images also demonstrated various morphologies, suggesting that the morphological differences observed in tissue corresponded to the cell lineage. These results indicate the possible application of SRS microscopy to dermatological investigation of cell lineages and types in the epidermis by cellular-level analysis.
We present new near-infrared (NIR) imaging technique for analyzing the moisturizer drop dynamics on the human skin surface. From the measurement experiment for the vertical water content in the skin tissue and light transport simulation, it was clarified that imaging the skin tissue using 1950 nm band effectively visualizes the water distribution. We demonstrate the NIR imaging experiment using originally developed NIR microscopic water imaging system. The relationship between the moisturizer drop dynamics and the water condition of the skin tissue is also discussed.
Wavelength-dependent light penetration depth in the measurement of water distribution of the skin tissue is analyzed. Near-infrared (NIR) imaging enables 2-D water content map on the skin tissue because water absorbs light strongly in the NIR region particularly around the wavelengths of 1450 and 1920 nm. However, the depth of the light penetration depends largely on wavelength as the absorption coefficient of water changes considerably in the NIR range. We investigate the measurement depth of the water content mapping with a NIR camera and bandpass filters at the wavelengths of 1300, 1450 and 1920 nm. Analysis is performed with Monte Carlo light scattering simulation adopting the optical parameters which is derived from the depth profile of the water contents measured by the confocal Raman spectroscopy. It is found that the NIR image in 1920 nm gives the highest sensitivity to the water content in the surface layer of the skin tissue.