Credit: © 2009 ACS

It is known that cells can endocytose (uptake) nanoparticles in a size-dependent manner. Gold nanoparticles with a diameter of 14–100 nm and DNA-wrapped single-walled carbon nanotubes shorter than 1 μm are internalized via receptor-mediated endocytosis — an uptake process where nanoparticles first bind to a receptor on the cell surface before inward budding of the membrane forms vesicles that transport the particles into the cell. Michael Strano and co-workers1 from MIT now report a quantitative model to correlate endocytosis with the geometry of the nanoparticle.

The team determined the rate constants for this trafficking process using a 'kinetic network model', which was validated by experiments using DNA-wrapped carbon nanotubes. The model asserts that small particles (∼25 nm) can be endocytosed, because as the nanoparticle–receptor complexes form clusters of sufficient size, the elastic energy and entropic barriers associated with the formation of vesicles are overcome, thereby driving the internalization. The uptake mechanism for gold nanoparticles was also modelled consistently using previously published data.

Such quantitative models may provide useful insights for engineering nanomaterials with a more well-defined efficacy, functionality and toxicity.