The scheme for the fabrication of the nanogels and property characterization. (a) Fabrication scheme of PPP, PPPM, PPD, PPPD, and PPPDM nanogels, and AEB-conjugated PPDA, PPPDA, and PPPDMA nanogels. A polymer or polymer mixture self-assembles in aqueous media and further crosslinks through disulfide bonds to form polymer nanogels, which could be further decorated with AEB. (b) Schematic illustration of the dual-stimuli-responsive drug release in cancer cells. After the nanogels are delivered into cancer cells through the sigma 2 and/or HER-2 facilitated self-delivery, on-demand drug release will be triggered by the elevated GSH and ROS within cancer cells. (c) TEM image and the size distribution spectrum acquired by DLS (insert) of PPPDMA nanogels. Scale bar is 100 nm. (d) Drug release profiles of PTX from PPP nanogels. (E) Drug release profiles of DOX from PPD nanogels. Schematic illustration of the bioactivatable self-quenched nanogel for targeted photodynamic therapy.