Photoswitchable upconversion nanophosphors for small animal imaging in vivo†
Photoswitchable upconversion luminescence nanoprobes (ps-UCNPs) are capable of adjusting the luminescent emission of upconversion nanocrystals and producing photoswitchable imaging by photochromism of molecular switch diarylethenes (DTEs). Here we present a rational, and simple strategy for constructing reversible ps-UCNPs based on NaYF4:Yb,Er,Tm nanocrystals and DTEs trapped in one nanosystem using BSA-graft-dextran copolymer as a shell to form a nanocapsule. In this nanosystem ps-UCNPs exhibited effective photochromic behavior and photoswitchable upconversion luminescence (UCL) which was controlled by alternating UV/visible light. Importantly, the ps-UCNPs showed low cytotoxicity and may be used as a photoswitchable UCL nanoprobe for in vitro and in vivo bioimaging. This is the first photoswitchable probe for mouse-level bioimaging in vivo. Our design strategy provides a versatile process for constructing a special photo-modulated probe in bioimaging.