UbasM: An effective balanced optical clearing method for intact biomedical imaging.

Optical clearing methods can facilitate deep optical imaging in biological tissue by reducing light scattering and this has enabled accurate three-dimensional signal visualization and quantification of complex biological structures. Unfortunately, existing optical clearing approaches present a compromise between maximizing clearing capability, the preservation of fluorescent protein emission and membrane integrity and the speed of sample processing - with the latter typically requiring weeks for cm scale tissue samples. To address this challenge, we present a new, convenient, aqueous optical clearing agent, termed UbasM: Urea-Based Amino-Sugar Mixture, that rapidly renders fixed tissue samples highly transparent and reliably preserves emission from fluorescent proteins and lipophilic dyes in membrane integrity preserved tissues. UbasM is simple, inexpensive, reproducible and compatible with all labeling methods that we have encountered. It can enable convenient, volumetric imaging of tissue up to the scale of whole adult mouse organs and should be useful for a wide range of light microscopy and tomography techniques applied to biomedical research, especially the study on organism-level systems biology at multiple levels.