Nanoparticles in a biological fluid (plasma, or otherwise) associate with a range of biopolymers, especially proteins, organized into the ''protein corona'' that is associated with the nanoparticle and continuously exchanging with the proteins in the environment. Methodologies to determine the corona and to understand its dependence on nanomaterial properties are likely to become important in bionanoscience. Here, we study the long-lived (''hard'') protein corona formed from human plasma for a range of nanoparticles that differ in surface properties and size. Six different polystyrene nanoparticles were studied: three different surface chemistries (plain PS, carboxyl-modified, and amine-modified) and two sizes of each (50 and 100 nm), enabling us to perform systematic studies of the effect of surface properties and size on the detailed protein coronas. Proteins in the corona that are conserved and unique across the nanoparticle types were identified and classified according to the protein functional properties. Remarkably, both size and surface properties were found to play a very significant role in determining the nanoparticle coronas on the different particles of identical materials. We comment on the future need for scientific understanding, characterization, and possibly some additional emphasis on standards for the surfaces of nanoparticles.bionanoscience ͉ mass spectrometry ͉ interactions ͉ proteomics ͉ human plasma

The importance of the protein corona formed around nanoparticles upon entering a biological fluid has recently been highlighted. This corona is, when sufficiently long-lived, thought to govern the particles' biological fate. However, even this long-lived "hard" corona evolves and re-equilibrates as particles pass from one biological fluid to another, and may be an important feature for long-term fate. Here we show the evolution of the protein corona as a result of transfer of nanoparticles from one biological fluid (plasma) into another (cytosolic fluid), a simple illustrative model for the uptake of nanoparticles into cells. While no direct comparison can be made to what would happen in, for example, the uptake pathway, the results confirm that significant evolution of the corona occurs in the second biological solution, but that the final corona contains a "fingerprint" of its history. This could be evolved to map the transport pathways utilized by nanoparticles, and eventually to predict nanoparticle fate and behavior.

We have analyzed the adsorption of protein to the surfaces of silica nanoparticles with diameters of 6, 9, and 15 nm. The effects upon adsorption on variants of human carbonic anhydrase with differing conformational stabilities have been monitored using methods that give complementary information, i.e., circular dichroism (CD), nuclear magnetic resonance (NMR), analytical ultracentrifugation (AUC), and gel permeation chromatography. Human carbonic anhydrase I (HCAI), which is the most stable of the protein variants, establishes a dynamic equilibrium between bound and unbound protein following mixture with silica particles. Gel permeation and AUC experiments indicate that the residence time of HCAI is on the order of approximately 10 min and slowly increases with time, which allows us to study the effects of the interaction with the solid surface on the protein structure in more detail than would be possible for a process with faster kinetics. The effects on the protein conformation from the interaction have been characterized using CD and NMR measurements. This study shows that differences in particle curvature strongly influence the amount of the protein's secondary structure that is perturbed. Particles with a longer diameter allow formation of larger particle-protein interaction surfaces and cause larger perturbations of the protein's secondary structure upon interaction. In contrast, the effects on the tertiary structure seem to be independent of the particles' curvature.