Traditional and innovative optical clearing agents

Abstract

The problem scientists face in increasing the accuracy of the optical diagnostic methods is successfully solved through the use of a well-developed tissue optical clearing (TOC) technique using optical clearing agents (OCAs) and methods for their incorporation into biological tissues. The ultimate goal of all TOC techniques is to match the refractive index throughout the tissue to reduce optical inhomogeneities causing light scattering; however, the approaches can be different depending on the scientific tasks involved: i) simple immersion with the use of hyperosmotic OCAs as one-component or multi-component solutions with different chemicals and/or physical enhancers; ii) immersion with previous dehydration and delipidation with the use of organic solvents; iii) hyperhydration with or without the use of detergents; and iv) hydrogel embedding with the use of fixation and crosslinking. This chapter focuses on features of traditional and innovative OCAs, the development and specialization of in vitro and in vivo (ex vivo) optical clearing approaches, and the diffusion coefficients of some OCAs in tissues.