Significance of cell “observer” and protein source in nanobiosciences

► Protein source has key role in the formation of the associated protein corona at the surface of nanoparticles. ► The nature of the proteins in the corona is determined by the local chemical properties of the nanoparticles. ► The cell “observer” effect has a great impact on nanoscale systems. ► Various cells respond (e.g. uptake and toxicity) differently to the exact same type/amount of nanoparticles.