When nanoparticles enter a biological fluid (blood, lung fluid, etc.) their surface is rapidly covered by a corona of proteins. This corona defined the biological safety or risk of the nanoparticle, because it is the particle with its corona that the biological system responds to. We have shown that the corona around many nanoparticles is remarkably specific and contains a small number of proteins, and their relative surface concentration is very far from a random representation of their relative occurrence in the body fluid. Further, we study how the corona composition changes over time, or when the nanoparticle travels from on body compartment to another. We develop methodology to identify nanoparticle-associated proteins, and measure their interaction parameters. We study nanoparticle-induced effects on protein aggregation and function. We connect our findings at the molecular level to testable hypothesis on functionthat may be perturbed at physiological level.