Reversible light-controlled fluorescence switch of block polymer-grafted carbon dots and cellular imaging

A novel type of aggregation-induced emission (AIE) nanoparticles, which are carbon dots (CDs) grafted with block polymer of tetraphenylethylene, spiropyran and N-isopropylacrylamide (CD-g-poly((TPE-co-SPA)-block-NIPAM)), was synthesized. The CD-g-poly((TPE-co-SPA)-block-NIPAM) nanoparticles can emit weak cyan fluorescence in tetrahydrofuran, while showing AIE-enhanced cyan fluorescence in water and solid film. The fluorescence of the CD-g-poly((TPE-co-SPA)-block-NIPAM) nanoparticles can reversibly transform cyan to red with UV/visible light irradiation, and functioned as a reversible fluorescence photoswitch. Importantly, the CD-g-poly((TPE-co-SPA)-block-NIPAM) nanoparticles have low cytotoxicity and, therefore, can be used for imaging in living cells.