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Protein rejecting properties of PEG-grafted nanoparticles: influence of PEG-chain length and surface density evaluated by two-dimensional electrophoresis and bicinchoninic acid (BCA)-proteinassay.

Poly (ethylene glycol) (PEG)-grafted nanoparticles have been described as potential intravenously injectable, long-circulating drug carriers. The in vivo behaviour of intravenous administered nanoparticles is decisively influenced by the interaction of the particles with the blood proteins. Two-dimensional electrophoresis (2-DE) was employed to study the protein rejecting properties of PEG-grafted polymer nanoparticles, possessing PEG-200 and PEG-400 chains, respectively. The calculated PEG-chain distances varied between 0.39/0.31 nm (PEG-200) and 0.39/0.34 nm (PEG-400), therefore it was possible to study the influence of high chain densities attained by the use of short PEG chains on the protein adsorption. Apart from a stronger protein rejection of small-MW proteins achieved by PEG-chain distance diminution, the affinity of several proteins for the PEG-chains are shown and discussed. Beside the study of protein adsorption patterns, the total protein mass adsorbed to the particles, as well as the extent of protein desorption prior to 2-DE, was investigated using the bicinchoninic acid (BCA)-protein assay.