Photon Upconversion Hydrogels for 3D Optogenetics

The ability to optically induce biological responses in three-dimensions (3D) has been dwarfed by the physical limitations of visible light penetration to trigger photochemical processes. However, many biological systems are relatively transparent to low-energy light, which does not provide sufficient energy to induce photochemistry in 3D. In this talk, I will present our strategy to overcome this challenge, by developing hydrogels that are capable of converting near-infrared (NIR) light into blue light within cell-laden 3D hydrogels. The upconverted light can then excite optically active proteins in cells to trigger a photochemical response. The hydrogels operate by triplet-triplet annihilation upconversion. As proof-of-principle, we find that the hydrogels trigger an optogenetic response by NIR irradiation of HeLa cells that have been engineered to express the blue-light sensitive protein Cry2olig. While it is remarkable to photoinduce the clustering of Cry2olig with blanket NIR irradiation in 3D, we also demonstrate how the hydrogels trigger clustering within a single cell with great specificity and spatiotemporal control. In principle, these hydrogels may allow for photochemical control of cell function within 3D scaffolds, which can lead to a wealth of fundamental studies and biochemical applications.