Microwave synthesis of ultrasmall gold nanoparticles, their γ-globulin interaction and subsequent effects in hepatocellular carcinoma cells

Gold nanoparticles (GNPs) are widely explored for biomedical applications; however, their interactions with plasma proteins and the resulting effects on biological activity remain insufficiently understood. In this study, ultrasmall GNPs were synthesized via a solvent-polarity-controlled microwave-assisted reduction method using sodium citrate as a reducing agent and polyvinylpyrrolidone as a stabilizer. The synthesized GNPs exhibited a mean diameter of 6 ± 2 nm and were subsequently employed to investigate the formation and biological implications of a γ-globulin protein corona. Physicochemical characterization demonstrated that γ-globulin adsorption significantly altered the colloidal properties of GNPs, resulting in increased hydrodynamic size, reduced zeta potential, and a red-shift of the surface plasmon resonance band. Fluorescence quenching studies revealed a spontaneous interaction between GNPs and γ-globulin. Thermodynamic analysis indicated that the binding process was predominantly driven by hydrogen bonding and van der Waals interactions. Molecular docking using Au₁₃ and Au₄₃ clusters as computationally tractable models of the GNP surface further confirmed the involvement of polar amino acid residues in protein adsorption. Spectroscopic analyses showed only minor conformational perturbations in γ-globulin following interaction with GNPs. Biological evaluation demonstrated that bare GNPs exerted significant selective antiproliferative activity against HepG2 hepatocellular carcinoma cells relative to normal human hepatic L-02 cells, whereas γ-globulin-coated GNPs exhibited markedly reduced cytotoxicity. Protein corona formation decreased cellular uptake, attenuated reactive oxygen species generation, preserved antioxidant defenses, and reduced apoptosis-related signaling. These findings establish a direct mechanistic relationship between γ-globulin corona formation, nanoparticle physicochemical properties, cellular uptake, and biological response, highlighting the critical role of the nano-bio interface in determining the therapeutic performance of GNP-based systems.