Reversible Fluorescence Switching of Spiropyran-Conjugated Biodegradable Nanoparticles for Super-Resolution Fluorescence Imaging

We report on the reversible fluorescence switching of biodegradable nanoparticles of spiropyran-terminated poly(e-caprolactone) (SP-PCL) for super-resolution fluorescence imaging. SP-PCL was synthesized via ring-opening polymerization using hydroxyl-containing SP derivative as the initiator. SP-PCL solution in THF or dioxane exhibits fast photochromism from colorless to blue upon UV irradiation due to the transformation of SPs in SP-PCL into merocyanines (MCs). Although both SP-PCL solution and MC-PCL solution do not fluoresce, SP-PCL nanoparticle dispersion fabricated via nanoprecipitation in aqueous media, in which SP molecules were embedded into the hydrophobic PCL matrix, displays considerable green emission at 530 nm at an excitation wavelength of 420 nm. Upon <420 nm irradiation, the resulting MC-PCL nanoparticles show strong red emission at 650 nm when excited at 420 nm. SP-PCL nanoparticles display green–red dual-color intrinsic fluorescence switching upon alternated UV/vis illumination. Green emi...