Reversible Optical Tissue Clearing Using Dye-Based Solutions for Ex Vivo and In Vivo Imaging

Dynamic imaging is critical in biology and medicine, but refractive index heterogeneities within biological tissues induce scattering that constrains penetration depth and degrades spatial resolution. Strongly absorbing molecules dissolved in aqueous solutions can modulate the refractive index of the surrounding medium through the Kramers–Kronig relation, thereby reducing mismatches between tissue components and mitigating scattering. In this work, we detail the preparation and characterization of dye-based solutions and their effectiveness in achieving optical tissue clearing in both ex vivo and in vivo samples. Our results demonstrate enhanced transparency in ex vivo tissue and reversible optical clearing in live animals, enabling clearer visualization of internal organs and structures. This approach establishes an accessible, non-invasive, and reversible strategy to improve imaging depth and clarity across biological systems.