Schematic views of nanoparticle delivery. (A) Nanoparticledelivery by passive targeting. In this mode, nanoparticles pass through theleaky vasculature and enter tumor tissues. (B) Nanoparticle delivery byactive targeting. In this mode, the surface of nanoparticles iscoated/conjugated with an active targeting moiety, such as peptide, antibody,or aptamer. Binding of the targeting moiety with cell surface moleculesfacilities tumor tissue entry of the nanoparticle.