Fast responsive photo-switchable dual-color fluorescent cyclodextrin nanogels for cancer cell imaging

Photo-switchable dual-color fluorescent nanogels were fabricated via nanoprecipitation in aqueous solution. The spiropyran-modified beta-cyclodextrin (beta-CD-SP) and 4-amino-7-nitro-1,2,3-benzoxadiazole (NBDNH2) were encapsulated into nanogels in the presence of 1,6-hexamethylene diisocyanate (HMDI). In the nanogels, spiropyran moiety acted as fluorescence molecule acceptors under the irradiation of UV or visible light to quench or recover the fluorescence of the NBDNH2 to achieve reversible dual-color fluorescence. The feed ratio of the two fluorophores played vital role on the energy transfer efficiency (E) of the nanogels, and the results showed that high E (90.7%) can be achieved when the feed ratio of NBDNH2/beta-CD-SP is 1:2 (mol/mol). In addition, the nanogels can maintain good photo-switchable fluorescent behavior as long as 5 weeks. With rapid photo-responsiveness (within 60 s), good reversibility, long-term stability, and excellent cytocompatibility, the as-prepared nanogels have been successfully applied to photo-switchable dual-color fluorescent imaging in cancer cell.