Effects of Surface Coating on Nanoparticle-Protein Adsorption Selectivity

Abstract

Negatively charged, uni-sized naked gold (Au) and coated poly (acrylic acid) (PAA)—polyethyleneimine (PEI)-Au (PPAu) nanoparticles (NP)s were incubated with four proteins of different molecular weights: bovine serum albumin (BSA) ~ 67 kDa, cationic trypsin ~ 23.3 kDa, LL-37 peptide ~ 4.5 kDa, and PK(FK)5PK peptide ~ 1.9 kDa. Different interaction kinetics were observed and analyzed by cryogenic transmission electron microscopy (cryoTEM) and UV-Vis spectroscopy. The naked Au NPs adsorbed all four proteins showing no selectivity towards any specific protein category, while PPAu NPs adsorbed only the LL-37 and PK(FK)5PK peptides (they did not adsorb BSA and cationic trypsin), thereby expressing selectivity to positively charged low molecular weight (LMW) proteins. Applying an interpretation of the Hill model, we showed that PPAu and naked Au NPs have similar affinity and cooperative binding behavior toward the PK(FK)5PK peptide. This study also supports the assumption that NP chemical composition may be a tunable property in NP design for specific applications such as LMW proteins’ harvesting, biosensing, and drug delivery systems. Although it may be speculated that surface structure may be shaped to enhance selective adsorption, this feature has not been demonstrated in the present study. Protein-NP interaction is an emerging field in biomedical research. Particularly Au NPs-protein interaction, due to the Au NPs promising medical applications inherited from their easy-to-make and surface functionalizing processes. This interaction depends on several factors, such as NP size, surface charge, and surface chemical composition and morphology. Herein, we studied the effect of NP surface coating on the adsorption behavior of various proteins of similar size, negatively charged naked Au, and coated PPAu NPs. Our findings suggest that the NPs’ surface morphology may play a major role in molecular weight (MW)-based NP-protein adsorption selectivity. Future work will focus on engineering new coated Au NPs with different polymers to gain better understanding regarding the effects of surface composition and manipulated morphology on the selective adsorption of proteins. Additionally, we will explore the potential role of selective protein adsorption in regenerative medicine bioresearch and applications.