Demonstration of the photo-controllability of the bistable opsin OPN5 using upconversion nanoparticles with multiple emission peaks upon near-infrared photoexcitation

Upconversion nanoparticles (UCNPs) have emerged as promising tools for deep tissue optogenetics because they can convert near-infrared (NIR) light, which has high biopermeability, into ultraviolet (UV) or visible light. In optogenetics, microbially derived photoreceptor proteins such as channelrhodopsin (ChR) have been widely used. G protein-coupled receptor (GPCR)-type opsins have signal amplification capabilities and are emerging as promising candidates for high-sensitivity optogenetic tools. Since many GPCR-type opsins are so-called "bistable opsins" that can be switched between active and inactive states using light, it is not obvious whether multi-wavelength light from UCNPs can control bistable opsins. In this study, we constructed HEK293T cells expressing OPN5, a type of bistable opsin, and bound NaYF₄:Yb,Tm@NaLuF₄ core-shell UCNPs onto the cells. It was then demonstrated that light emitted from UCNPs upon NIR irradiation can control OPN5 even when the wavelengths that activate and deactivate OPN5 are simultaneously emitted.