Ultrastable Fluorescent Polymer Dots for Stimulated Emission Depletion Bioimaging

Abstract Stimulated emission depletion (STED) nanoscopy is an emerging super‐resolution imaging technique, which enables high spatiotemporal characterization of cellular structures and dynamics. However, its current application is limited by the lack of photostable fluorophores, which can endure strong STED illumination. Herein, a type of photobleaching‐resistant semiconducting polymer dots (Pdots) for STED imaging is reported. The Pdots are synthesized by nanoprecipitation of the mixture of hydrophobic fluorescent polymer poly[{9,9‐dihexyl‐2,7‐bis(1‐cyanovinylene)fluorene}‐alt‐co‐{2,5‐bis(N,N′‐diphenylamino)‐1,4‐phenylene}] (PDFDP) and amphiphilic polymer poly(styrene‐co‐maleic anhydride) (PSMA) to form monodispersed nanoparticles. The Pdots show remarkable properties, including superior photostability, bright fluorescence, large Stokes shift, and easy surface functionalization. Imaging of individual Pdots is realized with a super‐resolution of 71 nm. Long‐term (2 h) continuous STED imaging of cellular Pdots and live‐cell STED imaging for dynamic tracking are achieved. These results demonstrate the promising potential of using Pdots as a new class of fluorescent probe for STED nanoscopy.