MACS: Rapid aqueous clearing system for three-dimensional mapping of intact organs

Tissue optical clearing techniques have provided important tools for large-volume imaging. Aqueous-based clearing methods are known for good fluorescence preservation and scalable size maintenance, but are limited by either long incubation time, or insufficient clearing performance, or requirements for specialized devices. Additionally, due to the use of high concentration organic solvents or detergents, few clearing methods are compatible with lipophilic dyes while maintaining high clearing performance. To address these issues, we developed a rapid, highly efficient aqueous clearing method with robust compatibility, termed m-xylylenediamine (MXDA)-based Aqueous Clearing System (MACS). MACS can render intact organs highly transparent in a fairly short time and possesses ideal compatibility with multiple probes, especially for lipophilic dyes. Using MACS, we cleared the adult mouse brains within only 2.5 days for three-dimensional (3D) imaging of the neural structures labelled by various techniques. Combining MACS with DiI labelling, we visualized the vascular structures of various organs. MACS provides a useful tool for 3D mapping of intact tissues and is expected to facilitate morphological, physiological and pathological studies of various organs.