Under electrostatic interactions, polyethylenimine-stabilized Fe3O4 magnetic nanoparticles were assembled with photosensitive nitric oxide (NO) donors (Fe4S3(NO7-)), RBS) and CuFL complex consisting of fluorescein derivatives (FL) and Cu-II to prepare Fe3O4-CuFL-RBS nanocomposites. The as-prepared nanocomposites exhibited weak fluorescence and hardly any release of NO upon light irradiation of 480 nm. The nanocomposites enabled NO release due to RBS photolysis under 365 nm light irradiation, while the released NO could in situ conjugate with CuFL to form FL-NO complex based on N-nitrosate reaction, which was verified by fluorescence increase responses of FL-NO (excited at 480 nm). Thus, Fe3O4-CuFL-RBS nanocomposites realized light-triggered NO release and turn-on fluorescence detection of NO in situ. (C) 2015 Elsevier B.V. All rights reserved.