PGP and neoplasm: To solve this problem, Zeng and his colleagues (2018) firstly synthesized black phosphorus nanosheets by liquid-phase exfoliation technique and loaded DOX and P-gp siRNA on the surface; then they coated the nanosheets with highly biocompatible polydopamine (PDA) to maintain their structural and functional stability, modified NH2-PEG-Apt on the surface to achieve active drug delivery to tumor cells and constructed a kind of multifunctional co-delivery drug system (BP-R-D@PDA-PEG-Apt).