Engineering Protein-Gold Nanoparticle/Nanorod Complexation via Surface Modification for Protein Immobilization and Potential Therapeutic Applications

Gold nanoparticles (AuNPs) and nanorods (AuNRs) find broad applications due to their unique optical and chemical properties. In biological applications, the contact of AuNPs/AuNRs with proteins is inevitable, resulting in the formation of a protein corona, protein-particle agglomerates, or particle precipitation. While nonspecific adsorption or particle precipitation should be avoided, controllable protein adsorption and agglomerate formation via surface modification find applications in protein immobilization and therapeutics. Therefore, it becomes essential to understand the influences of particle surfaces on protein adsorption. Recently, we found a problematic globular protein, T4 lysozyme (T4L), precipitating AuNPs [Neupane et al. J. Phys. Chem. C. 2017, 121, 1377-1386]. Herein, we systematically investigated the effects of surface modification on the adsorption of T4L. We found that both positively charged and neutral polymer coatings are effective in preventing such precipitation. In addition, for AuNPs with negative coatings, T4L could form either a stable protein corona or agglomerates, depending on the coating. For T4L and negatively coated AuNRs, only coronas were formed regardless of coating thickness. In all cases, we utilized EPR to detect protein rotational tumbling and backbone dynamics, which revealed the local environment that T4L experiences in these complexes. Such information is important for guiding future designs of gold nanomaterial protein complexes with desired functions. Our findings demonstrate the importance of coatings on AuNP/AuNR functions in biological environments. With negative coatings, AuNPs/AuNRs can serve as immobilizers for carrying positively charged proteins. Furthermore, with proper coatings, a precipitation-causing protein could facilitate the formation of AuNP-based agglomerates which can have thermotherapeutic applications.