Limits of transparency in biological tissues via Refractive Index matching

Biological tissues strongly scatter light due to refractive index variations at cellular and sub-cellular scales. This turbidity restricts optical imaging and therapeutic depth, limiting the effectiveness of light-based biomedical techniques. Tissue clearing strategies, such as immersion in refractive index–matching agents, can reduce scattering and improve transparency. However, the ultimate physical limits of how transparent a tissue can become remain largely unexplored. In this work, we investigate tissue as a model system for understanding these transparency boundaries. Using optical clearing agents (OCA), we examine how the optical properties of tissues are modified. By extending the study across multiple species, we aim to identify universal and species-specific behaviours that shape the optical transparency of biological tissue. Our results provide new insight into the interplay of scattering, absorption, and intrinsic tissue structure in defining transparency limits. This framework contributes to the physics of light–tissue interactions and has implications for optimizing biomedical imaging systems and clearing protocols.