Influence of nanoparticle size on the pH-dependent structure of adsorbed proteins studied with quantitative localized surface plasmon spectroscopy

We have studied p H-dependent conformational transitions of Bovine Serum Albumin adsorbed onto different sizes of gold nanospheres. For larger spheres (D > 10 nm) there is evidence for a path-dependent extended state near p H 4, over a very small p H range. For smaller nanospheres (5nm and 10nm) the evidence for such a transition is either much weaker or completely suppressed. We suggest that the absence of the transition on small spheres is due to the fact that the protein adsorbed on such small spheres has already lost at least some of its tertiary structure. The results have important implications for the functionality of proteins adsorbed onto nanospheres or surfaces with nm scale roughness.