Subcellular Optogenetics Enacted by Targeted Nanotransformers of Near-Infrared Light

Light activation of photoswitchable molecules enables control over the course of physicochemical processes with high spatiotemporal precision, offering revolutionizing potential in multiple areas of contemporary biomedicine. Yet, application of this technology in live organisms remains severely limited due to the reliance on visible light that has poor penetration in biological tissues. Herein, we introduce highly efficient upconversion nanoparticles (UCNPs) as photon nanotransformers that intracellularly convert tissue-penetrating, near-infrared light into visible light required for photoactivation. The core/shell nanoparticles described here are determined to be about six times brighter in the blue range than the canonical hexagonal (NaYF₄:Yb³⁺30%/Tm³⁺0.5%)/NaYF₄ core/shell UCNPs with record efficiency. An application of such efficient photon nanotransformers can significantly advance optogenetics technology, wherein the signaling of genetically modified neurons is controlled through interaction of visible light with optogenetic proteins inserted into the cell membranes. We demonstrate that our photon nanotransformers, targeted to cultured cells, enable optogenetic activation with incident near-infrared light. The resulting membrane potential modulation by ion channel activity is probed by Ca ²⁺ sensitive dye. In contrast to conventional optogenetic approaches involving unselective activation of optogenetic proteins in the cellular volume with incident light irradiation, the upconverted light generated in situ by intracellular UCNPs, activates the optogenetic proteins in close vicinity to the nanoparticles, thus, providing a high subcellular precision of photoactivation.