Interaction of fibrinogen and albumin with titanium dioxide nanoparticles of different crystalline phases

TiO₂ nanoparticles (NPs) are contained in different kinds of industrial products including paints, self-cleaning glasses, sunscreens. TiO₂ is also employed in photocatalysis and it has been proposed for waste water treatment. Micrometric TiO₂ is generally considered a safe material, while there is concern on the possible health effects of nanometric titania. Due to their small size NPs may migrate within the human body possibly entering in the blood stream. Therefore studies on the interaction of NPs with plasma proteins are needed. In fact, the interaction with proteins is believed to ultimately influences the NPs biological fate. Fibrinogen and albumin are two of the most abundant plasma proteins. They are involved in several important physiological functions. Furthermore, fibrinogen is known to trigger platelet adhesion and inflammation. For these reasons the study of the interaction between these protein and nanoparticles is an important step toward the understanding of the behavior of NPs in the body. In this study we investigated the interaction of albumin and fibrinogen with TiO₂ nanoparticles of different crystal phases (rutile and anatase) using an integrated set of techniques. The amount of adsorbed fibrinogen and albumin for each TiO₂ surface was investigated by using the bicinchoninic acid assay (BCA). The variation of the surface charge of the NP-protein conjugates respect to the naked NPs was used to indirectly estimate both surface coverage and reversibility of the adsorption upon dilution. Surface charge was monitored by measuring the ζ potential with a conventional electrophoretic light scattering (ELS) system. The extent of protein deformation was evaluated by Raman Spectroscopy. We found that both proteins adsorb irreversibly against electrostatic repulsion, likely undergoing conformational changes or selective orientation upon adsorption. The size of primary particles and the particles aggregation rather than the crystal phase modulate the affinity of fibrinogen for the TiO₂ surfaces.