Understanding the Stability of Nanoparticle–Protein Interactions: Effect of Particle Size on Adsorption, Conformation and Thermodynamic Properties of Serum Albumin Proteins

The present work evaluates the effect of nanoparticle size on the structure and function of albumin proteins. Further, the work evaluates the nature of binding between low molecular weight (∼20 kDa) chitosan oligosaccharide nanoparticles (COS NPs) and high molecular weight (∼85–90 kDa) chitosan nanoparticles (CS NPs) with two model proteins, namely, human serum albumin (HSA) and bovine serum albumin (BSA). The size-dependent pattern of protein-adsorption onto nanoparticle surface was studied using dynamic light scattering and further quantified by size exclusion chromatography-HPLC method. Circular dichroism spectroscopy revealed that both the proteins underwent conformational change upon association with the cationic nanoparticulate systems. Further, fluorescence spectroscopy was used to probe the stability of nanoparticle–protein complexes, by determining the binding constants of nanoparticle to protein and to evaluate the thermodynamic parameters of the interacted proteins. Smaller-sized NPs, in case of both the polymers, exhibited greater protein binding and increased conformational loss in proteins. Also, CS NPs resulted in lesser change in protein structure, thereby indicating a better biocompatibility than COS NPs. This observation was supported by the results of fluorescence spectroscopy, which implicated that the CS NPs (110 nm) formed the most stable, ground-state complex with HSA, which had a binding constant (Kb) of 6.76 × 104 M–1. Results from this investigation provide valuable insights into the molecular level interactions taking place at nanobiointerfaces, which can help in engineering stable, nanoscale materials of chitosan biopolymer and will be helpful to understand the nanoparticle toxicity for biomedical applications.