Figure 5.

Schematic depiction of the interplay between membrane receptors (depicted as cups) and NP surface ligands (depicted as gray spheres). (a) The number of ligands offered to the receptors is insufficient to induce invagination, either because (left) the NP or (right) the density of functional groups is too small. To allow for a sufficiently large number of ligand–receptor interactions, an extreme (and unrealistic) membrane curvature (dashed) would be required. (b) The number of successful receptor interactions can be increased by either clustering small NPs or having high densities of functional groups on larger NPs.