Structural modification of proteins adsorbed on silica nanoparticles: effect of the surface functionalization

The biological response elicited in cells by a material is strongly affected by the conformation, density and orientation of plasma proteins that adsorb on its surface, actually constituting new “bioactive sites” available for the interaction with cellular receptors. Type and extent of possible conformational changes in adsorbed proteins depend, in turn, on the peculiar physical-chemical surface properties of the materials. In these respect the events occurring after the interaction of Bovine Serum Albumin (BSA), which represent the major constituent (60%) of the serum proteins, with omogeneous spherical pure (hydroxyl-rich) silica and ammine-functionalized silica nanoparticles were investigated by two main complementary approaches: the measurement of the adsorbed amounts and the investigation of the structure of adsorbed proteins. In order to quantitatively asses the degree of surface covering, the surface area actually available for protein adsorption for both materials was determined by studying the agglomeration state of NPs when suspended in protein solutions (Dyamic Light Scattering and ζpotential measurements). As for the structural investigation of the interface layer, complementary spectroscopic techniques sensitive to different levels of the protein structure were used: modifications of secondary structures were investigated by CD-UV, whereas features of aromatic aminoacids residues were investigated by photoluminescence spectroscopy.