Rapid immunostaining method for three-dimensional volume imaging of biological tissues by magnetic force-induced focusing of the electric field.

Recent surges in tissue clearing technology have greatly advanced 3-dimensional (3D) volume imaging. Cleared tissues need to be stained with fluorescence probes for imaging but the current staining methods are too laborious and inefficient for thick 3D samples, which impedes the broad application of clearing technology. To overcome these limitations, we developed an advanced staining platform named EFIC in which a magnetic force focuses the electric field by bending it onto the sample. Such that EFIC applies a significantly lower electric field to maintain nanoscale structural integrity while effectively drives staining probes into pre-cleared 3D samples. We found that EFIC achieved a rapid and uniform staining of various proteins and vascular networks of the brain as well as other organs over the entire depth of imaging. EFIC stained tau deposits and the vascular structure in the post-mortem human brain of Alzheimer's disease and intracerebral hemorrhage, respectively, enabling quantitative analysis. The effectiveness of EFIC was further extended by the successful staining of various targets in non-cleared 3D brain samples. Together, EFIC represents a versatile and reliable staining platform for rapidly analyzing 3D molecular signatures and can be applied to sectioning-free 3D histopathology for diagnostic purposes.