Polyvinyl Alcohol Assisted Citrate Mediated Reduction of Gold(III) Salt: Theoretical Design and Experimental Study on Green Synthesis of Spherical and Biocompatible Gold Nanoparticles

Abstract

In this study, we demonstrate the synthesis of small gold nanoparticles (typically 8-10 nm) by a green synthesis approach. This method involves utilizing chloroauric acid as a gold precursor, trisodium citrate as a mild reducing and co-capping agent, and polyvinyl alcohol (PVA), as a co-capping and shape-directing agent. This novel synthesis method stands alone as a protocol that involves just mixing the reagents at room temperature and allowing the reaction to proceed at ambient temperature without any disturbance. In the absence of PVA, the morphology of gold nanoparticles transforms into nanowire networks (NWNs), eventually precipitating into gold foam or spongy gold. The synthesis process was meticulously tracked using time-resolved monitoring of the growth of the localized surface plasmon resonance by UV-vis spectroscopy and transmission electron microscopy. The as-prepared colloidal gold solution was bright red, attributed to the small size (< 10 nm) and spherical geometry of nanoparticles. This colloidal solution could be stored indefinitely at room temperature without precipitation or a change in its absorption profile. The nanoparticles remained stable in adverse conditions like 100 mM NaCl solution, 1× PBS and cell culture medium. Additionally, they could be easily loaded with drugs like doxorubicin by adsorption. The particles have been thoroughly characterized using a range of techniques, including UV-vis spectroscopy, attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), high-resolution transmission electron microscopy (HRTEM), Hyperspectral-Enhanced Dark Field Microscopy, dynamic light scattering (DLS), and X-ray photoelectron spectroscopy Cell viability tests conducted on 2D cell lines as well 3D spheroids revealed negligible toxicity even at high concentrations. Furthermore, we demonstrate that an advanced version of conventional diffusion-limited aggregation (DLA) schemes, which allows individual clusters to move freely within a domain to form larger aggregates, can effectively replicate the intricate interactions between chloroauric acid, trisodium citrate, and PVA, the agents involved in the synthesis of gold nanoparticles.

Keywords: Gold nanoparticles, Green synthesis, Cytotoxicity, Polyvinyl alcohol, Diffusion-limited aggregation, Dark field microscopy