Research and application of tissue optical clearing technique

BACKGROUND: Whole-body cell analysis of organisms is one of the major challenges in biomedicine. Tissue optical clearing technique combined with optical imaging and image processing technique can make the whole organ or the body transparent rapidly for structural and cellular analyses, providing a very promising solution for the application of advanced optical technique in life science. OBJECTIVE: To analyze the principle and process of tissue optical clearing technique, to summarize the research progress of tissue optical clearing technique, to present imaging technology for tissue clearing, and to discuss the application of tissue optical clearing technique in biomedical researches. METHODS: The first author searched relevant literatures in PubMed database with the keywords of “tissue optical clearing technique, tissue optical clearing, whole-body imaging and 3D imaging”. A total of 168 articles were initially retrieved. After sorting and screening systematically, 72 literatures were included for analysis, summary and discussion. RESULTS AND CONCLUSION: Current tissue optical clearing protocols are divided into two groups: solvent-based clearing methods and hydrophilic reagent-based clearing methods. Tissue clearing is usually conducted by the following steps: (a) tissue fixation, (b) permeabilization, (c) decolorization, and (d) refractive index matching. Tissue optical clearing technique can rapidly transform tissue into an optically transparent form, improving imaging depth and contrast. Combined with microscope imaging techniques such as confocal, two-photon and light sheet microscopes, tissue clearing can achieve 3D imaging of the whole organ or body at cellular resolution, accelerating the process of whole-body cell analysis of organisms. Tissue optical clearing technique will continue to evolve in the future, promote the development of new clearing reagents and clearing optimized microscopes, further enhance the acquisition of structural and molecular information from intact systems and contribute to the comprehensive understanding of whole biological systems.