Cationic Liposomes Enable Shape Control in Surfactant-Free Synthesis of Biocompatible Gold Nanorods

Shape-directing agents that promote anisotropic growth are frequently employed in the synthesis of gold nanorods (GNRs), a typical example of which is the surfactant cetyltrimethylammonium bromide (CTAB). Owing to their cytotoxicity, surfactant-passivated GNRs have little use in biological applications unless made biocompatible via additional downstream processing. Reported herein is the first instance of liposome-directed anisotropic growth of GNRs synthesized in the absence of surfactants. The as-synthesized phospholipid-passivated GNRs are readily biocompatible. Among the phospholipids tested, only liposomes prepared from 1,2-dioleoyl-sn-glycero-3-ethylphosphocholine (DOEPC)—a cationic transfection agent employed in lipid-mediated gene transfer in vitro—were capable of exerting shape control. By modifying a previously reported photochemical synthesis method, we developed a one-pot, seedless, DOEPC-mediated thermochemical synthesis method that yielded GNRs with an average size of 80–100 nm and an average aspect ratio of ∼3.5 and whose tips shape transformed from smooth to sharp during the course of the synthesis. Further characterization of the as-synthesized phospholipid-passivated GNRs confirmed its stability, excellent biocompatibility, photothermal transduction ability, and application in plasmonic photothermal therapy which was validated via GNR-mediated photothermal ablation of cancer cells in vitro, thus making this route of synthesis attractive for biological applications.