Enhancing Optical Transparency in Biological Tissues Using Photonics Engineering*

Dynamic imaging is a pivotal tool for answering complex scientific questions across physics and biology. However, traditional optical imaging platforms are hampered by the inadequate penetration depth in biological tissues, which restricts our understanding of dynamic behaviors at the fundamental level. The complex structure of biological matter, while enabling a tremendous diversity of functions, also causes opacity due to unwanted scattering and absorption of light, which limits the penetration depth of optical imaging. In most tissues, the scattering coefficient is 10−1000 times larger than the absorption coefficient; thus, scattering processes can severely limit the imaging depth and spatial resolution in conventional microscopy. Thus, if one could achieve significant reductions in light scattering, this could lead to significant enhancement of brightfield, fluorescence, nonlinear, and super-resolution imaging techniques.

 

In this talk, I will discuss the utilization of photonics engineering to achieve optical transparency in biological tissues. The turbid of the tissue originates from the microscale refractive index heterogeneity of the biological tissue. Light scattering in tissue originates from the difference between low refractive index  aqueous-based components (e.g., the interstitial fluid and cytosol) and high refractive index lipid- and protein-based components (e.g., the plasma membrane, myelin, and myofibrils). Leveraging Kramers-Kronig relations in the visible region, we integrate molecules that significantly absorb light into a scattering medium and transform an opaque sample into a transparent window, allowing deep investigation into embedded anatomical features. Utilizing this innovation, I have developed non-invasive imaging techniques to analyze the dynamics of neural networks in the peripheral nervous system, without the need for complex surgery. These innovations not only expand the toolbox available for high-resolution dynamic imaging but also underscore the potential of photonics to revolutionize our understanding of complex material and biological systems.