Comparative Analysis of Au and Au@SiO₂ Nanoparticle–Protein Interactions for Evaluation as Platforms in Theranostic Applications

Gold nanoparticles are utilized in a variety of sensing and detection technologies because of their unique physiochemical properties. Their tunable size, shape, and surface charge enable them to be used in an array of platforms. The purpose of this study is to conduct a thorough spectroscopic characterization of Au and functionalized hybrid Au@SiO₂ nanoparticles under physiological conditions and in the presence of two proteins known to be abundant in serum, bovine serum albumin and human ubiquitin. The information obtained from this study will enable us to develop design principles to synthesize an array of surface-enhanced Raman spectroscopy-based nanoparticles as platforms for theranostic applications. We are particularly interested in tailoring the surface chemistry of the Au@SiO₂ nanoparticles for applications in theranostic technologies. We employ common spectroscopic techniques, with particular emphasis on circular dichroism and heteronuclear single quantum correlation nuclear magnetic resonance (HSQC NMR) spectroscopy, as combinatorial tools to understand protein conformational dynamics, binding site interactions, and protein corona for the design of nanoparticles capable of reaching their intended target in vivo. Our results conclude that protein adsorption onto the nanoparticle surface prevents nanoparticle aggregation. We observed that varying the ionic strength and type of ion influences the aggregation and aggregation rate of each respective nanoparticle. The conformation of proteins and the absorption of proteins on the surface of Au nanoparticles are also influenced by ionic strength. Using two-dimensional [¹⁵N–¹H]-HSQC NMR experiments to compare the interactions of Au and Au@SiO₂ nanoparticles with ¹⁵N-ubiquitin, we observed small chemical shift perturbations in some amino acid peaks and differences in binding site interactions with ubiquitin and respective nanoparticles.