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Nanoparticles entering the bloodstream may initially bind highly abundant serum/plasma proteins, such as human serum albumin (HSA). We show here that, as a result of its low affinity and fast exchange, HSA is soon replaced by the higher-affinity and slower-exchanging apolipoproteinsAI, AII, AIV, and E, and that these proteins remain associated with the particles under the expected conditions of in vivo exposure, thus conferring their biological identity onto the particles.

The need to understand nanoparticles in a biological environment is now shared by nanobiology, nanomedicine, and nanotoxicology. There is currently considerable debate as to the nanoparticle characteristics that are important in determining biological response, including size, shape, and surface area.[1–3] New and interesting approaches to understanding the impact of interaction with nanoparticles on protein behavior are emerging.[4, 5] We have recently argued [6] that the effective unit of interest in the cell–nanomaterial interaction is not the nanoparticle in itself, but the particle and its “corona” of more or less strongly associated proteins from plasma or other bodily fluids. Ultimately, this corona of native-like or unfolded proteins “expressed” at the surface of the particle is “read” by living cells, and is the key phenomenon that scientists need to understand. Given this, it is surprising that the particle–protein complex is so poorly understood. We believe that the present study is the first reliable analysis of the proteins that associate to a nanoparticle in a complex biological fluid, and we present it as a guide for future studies in this area.