Improving in vitro biocompatibility of gold nanorods with thiol-terminated triblock copolymer

Abstract

Gold nanorods (AuNRs) are usually synthesized using cetyltrimethylammonium bromide (CTAB) surfactant as a structure-directing agent. CTAB is reported to form a tightly bound cationic bilayer on AuNR surface with the cationic trimethylammonium head group exposed to the aqueous media. However, CTAB is also known to be highly toxic in both in vitro and in vivo experiments. In this work, we investigated the cytotoxicity, colloidal stability and optical properties of AuNRs before and after substitution with thiol-terminated triblock copolymer of ethylene oxide-propylene oxide (PEO-PPO-PEO), or Pluronic F127® (PF127). For that, PF127 was first chemically functionalized with 3-mercaptopropionic acid (MPA) and further used as stabilizer for the AuNRs by replacing CTAB molecules. Unmodified PF127 was also tested and used as a control for biological experiments. Morphology of coated AuNRs was characterized by visible spectroscopy, transmission electron microscopy, zeta potential, and dynamic light scattering. We found that coating with PF127-SH guarantees both stability and biocompatibility of AuNRs for at least 45 days, besides improving cell viability when compared to the PF127-coated AuNRs, even after 72 h treatment. In addition, this new polymer coating can also provide hydrophobic domains assembled into the PPO blocks, which could be further loaded with organic active ingredients. The obtained results show the potential of this nanostructured system for future developments in multifunctional nanoplataforms for clinical applications such as drug delivery, hyperthermia, photodynamic therapy, and diagnostic imaging of cells and tissues.