Photofluorochromic water-dispersible nanoparticles for single-photon-absorption upconversion cell imaging.

Photofluorochromic diarylethene (DAE) molecules have been widely investigated due to their excellent fatigue resistance and thermal stability. However, the poor water solubility of DAEs limits their biological applications to some extent. Herein, we reported two kinds of water-dispersible DAE nanoparticles (DAEI-NPs and DAEB-NPs), in which DAE molecules were stabilized by the amphiphilic polymer DSPE-mPEG2000 using the nanoprecipitation approach. The fabricated nanoparticles retain well-controlled luminescence and fluorescence photoswitching properties in aqueous solution, which could be reversibly switched on and off under the alternating irradiation of ultraviolet (UV) and visible light. In addition, the closed-ring isomers of DAEB-NPs performed hot-band-absorption-based photon upconversion when excited by a 593.5 nm laser. Bearing excellent photophysical properties and low cytotoxicity, DAEB-NPs were applicable for upconversion cell imaging without high-excitation power density and free from oxygen removal. Additionally, the imaging process could be switched on by regulating the photofluorochromic nanoparticles.