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REVIEW: Methods for Optical Skin Clearing in Molecular Optical Imaging in Dermatology

A. Yu. Sdobnov1,2,a*, J. Lademann3, M. E. Darvin3#, and V. V. Tuchin2,4,5,6#

1Faculty of Information Technology and Electrical Engineering, University of Oulu, 90570 Oulu, Finland

2Research-Educational Institute of Optics and Biophotonics, Saratov State University, 410012 Saratov, Russia

3Center of Experimental and Applied Cutaneous Physiology, Department of Dermatology, Venerology and Allergology, Charité – Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, 10117 Berlin, Germany

4Laboratory of Laser Diagnostics of Technical and Living Systems, Institute of Precision Mechanics and Control, Russian Academy of Sciences, 410028 Saratov, Russia

5Interdisciplinary Laboratory of Biophotonics, Tomsk State University, 634050 Tomsk, Russia

6Bach Institute of Biochemistry, Research Center of Biotechnology of the Russian Academy of Sciences, 119071 Moscow, Russia

* To whom correspondence should be addressed.

# These authors contributed equally to this work.

Received August 15, 2018; Revised August 15, 2018; Accepted August 15, 2018
This short review describes recent progress in using optical clearing (OC) technique in skin studies. Optical clearing is an efficient tool for enhancing the probing depth and data quality in multiphoton microscopy and Raman spectroscopy. Here, we discuss the main mechanisms of OC, its safety, advantages, and limitations. The data on the OC effect on the skin water content are presented. It was demonstrated that 70% glycerol and 100% OmnipaqueTM 300 reduce the water content in the skin. Both OC agents (OCAs) significantly affect the strongly bound and weakly bound water. However, OmnipaqueTM 300 causes considerably less skin dehydration than glycerol. In addition, the results of examination of the OC effect on autofluorescence in two-photon excitation and background fluorescence in Raman scattering at different skin depths are presented. It is shown that OmnipaqueTM 300 is a promising OCA due to its ability to reduce background fluorescence in the upper skin layers. The possibility of multimodal imaging combining optical methods and OC technique is discussed.
KEY WORDS: multiphoton microscopy, Raman spectroscopy, Raman microscopy, tissue, skin, optical clearing, dehydration

DOI: 10.1134/S0006297919140098