Atomic Force Microscopy and Analytical Ultracentrifugation for Probing Nanomaterial Protein Interactions

Upon contact with the human body, nanomaterials are known to interact with the physiological surroundings, especially with proteins. In this context, we explored analytical methods to provide biologically relevant information, in particular for manufactured nanomaterials as produced by the chemical industry. For this purpose, we selected two batches of SiO2 nanoparticles as well as four batches of CeO2 nanoparticles, each of comparably high chemical purity and similar physicochemical properties. Adsorption of serum proteins and bovine serum albumin (BSA) was quantified by SDS-PAGE in combination with densitometry and further investigated by atomic force microscopy (AFM) and analytical ultracentrifugation (AUC). The protein adsorption to SiO2 nanoparticles was below the limit of detection, regardless of adjusting pH or osmolality to physiological conditions. In contrast, the four CeO2 nanomaterials could be classified in two groups according to half-maximal protein adsorption. Measuring the work of adhesion and indention by AFM for the BSA-binding CeO2 nanomaterials revealed the same classification, pointing to alterations in shape of the adsorbed protein. The same trend was also reflected in the agglomeration behavior/dispersibility of the four CeO2 nanomaterials as revealed by AUC. We conclude that even small differences in physicochemical particle properties may nevertheless lead to differences in protein adsorption, possibly implicating a different disposition and other biological responses in the human body. Advanced analytical methods such as AFM and AUC may provide valuable additional information in this context.