The key role of protein-nanoparticle interactions in nanomedicine and nanotoxicity has begun to emerge recently with the development of the idea of the nanoparticle-protein 'corona'. This dynamic layer of proteins (and other biomolecules) adsorbs to nanoparticle surfaces immediately upon contact with living systems. While within the biomaterials field the role of adsorbed molecules in cellular responses is acknowledged, there are several new issues at stake where nanoparticles are concerned. We show here that highly selective protein adsorption, added to the fact that particles can reach subcellular locations, results in significant new potential impacts for nanoparticles on protein interactions and cellular behavior.