Fig. 5. (A) Chemical structure of a reactive oxygen species (ROS) responsive polymer. (B) The mechanism of ROS responsive nanoparticles (S-NPs) complexed with DNA (S-NPs/DNA) to the transgene expression. (C) CLSM images of HeLa cells incubated with YOYO-1 labeled S-NPs/DNA complexes (C1) in the dark, and with light irradiation for (C2) 2 min and (C3) 5 min. Green: YOYO-1 fluorescence (E _x: 488 nm; E _m: 505–525 nm); red: S-NPs fluorescence (E _x: 405 nm; E _m: > 560 nm). Yellow: co-localization of red and green pixels. (C4) CLSM image illustrating the localization of YOYO-1–DNA after light irradiation with a further 4 h incubation. Green: YOYO-1 fluorescence; red: living nuclei stained with DRAQ5 (E _x: 633 nm; E _m: > 650 nm); yellow: co-localization of red and green pixels. Reprinted with permission from ref. 30. Copyright 2015 Wiley-VCH.