Small nanoparticles have less ligand-to-receptor interaction than do larger nanoparticles.
A 5-nm nanoparticle coated with 50-kDa proteins may interact with only one or two cell
receptors. By contrast, a 100-nm nanoparticle has many more ligand-receptor interactions per
particle. Several small ligand-coated nanoparticles must bind to receptors in close proximity to
one another to produce enough free energy to drive membrane wrapping