Figure 1.

Nanoparticle targeting mechanisms. A. Nanoparticles perform nonspecific passive targeting by diffusing and aggregating through leaky vessel in solid tumors via EPR effect. B. Nanoparticles modified with targeting agents perform active targeting on tumor cells expressing specific receptors. Nanoparticles specifically target on metastatic cancer cells. C. Fate of nanoparticles in non-specific gene delivery: phagocytosis, decomposition of nanoparticles outside of cells, and for the lipid or surfactant-based nanoparticles, the nanoparticles infuse into the cell membrane bilayers for drug release. D. Nanoparticles modified with targeting ligands specifically bind onto the membrane receptor and induce endocytosis. Higher proportion of gene molecules may eventually enter into nucleus.