We report on the reversible fluorescence switching of biodegradable nanoparticles of spiropyran-terminated poly (ε-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 ...