Raman microscopy for skin evaluation
Many dermatological studies have had limited success in revealing skin function because conventional histological methods are known to affect skin components. Recent progress in non-invasive optical imaging has enabled non-invasive visualization of the structure of each skin layer. However, it remains difficult to identify individual skin components. Alternatively, it is possible to obtain molecular vibrational signatures using spontaneous Raman scattering microscopy. Spontaneous Raman scattering microscopy requires long acquisition times and is rarely applied to skin imaging, especially because skin components, such as water and transepidermal agents, undergo relatively rapid changes. Consequently, non-linear Raman microscopies, such as coherent anti-Stokes Raman scattering and stimulated Raman scattering, have gradually been applied to acquire molecular imaging of skin tissue. In this review, the applications of Raman microscopies used to evaluate skin and research trends are presented. The applications of spontaneous Raman microscopy to in vivo human skin evaluation are first demonstrated with typical applications. Finally, the latest application of coherent Raman scattering microscopy to visualize 3D intracellular morphologies in the human epidermis during differentiation is described.