Optical transparency in live animals: a leap toward deep-tissue applications

The application of light remains constrained in deep tissues, where we struggle to achieve the same or comparable high-resolution focusing and imaging as in superficial tissues. This limitation mainly arises from the spatial inhomogeneities of refractive index (RI) in biological tissues, where light propagation is severely hindered by scattering and absorption. In recent years, enhancing imaging outcomes by reducing the scattering effects in tissues has become a hot topic of research. One effective way is to increase the refractive index of the aqueous components with optical clearing agents, achieving an effective RI level closer to that of lipids and proteins. This article comments on a recent study that reported a counterintuitive yet plain approach to the barrier and achieved biocompatible transparency of live tissues. In brief, the proposed strategy enables harmless, reversible tissue clarification of living rodents, greatly increasing the penetration depth and resolution of current in-vivo imaging technologies.