Embelin-Mediated Green Synthesis of Quasi-Spherical and Star-Shaped Plasmonic Nanostructures for Antibacterial Activity, Photothermal Therapy, and Computed Tomographic Imaging

Plasmonic nanostructures of silver and gold synthesized by conventional toxic and cumbersome methodologies raise huge concern for their clinical application, which necessitates the use of a greener approach. Herein, embelin, a benzoquinone derivative extracted from the fruits of Embelia tsjeriam-cottam, with immense medicinal value, is used as a reducing and stabilizing agent for the synthesis of quasi spherical gold and silver nanoparticles as well as gold nanostars. A sunlight-assisted synthesis resulted in embelin-stabilized silver nanoparticles of bimodal size distribution (similar to 3 and 15 nm) with potent antibacterial activity against Staphylococcus aureus and Escherichia coli. Similarly, embelin was also used for the synthesis of polyhedral gold nano particles of 12-15 nm in size and absorbance at 540 nm. These highly faceted and multitwinned gold nanoparticles facilitated the formation of 120 nm sized embelin-stabilized gold nanostars absorbing at NIR wavelength (800 nm). The embelin-stabilized nanoparticles demonstrated excellent compatibility toward cells and human blood. Additionally, the gold nanostars exhibited superior computed tomographic (CT) contrast characteristics and marked photothermal cytotoxicity toward oral epithelial carcinoma cells. This study thus proposes, for the first time, the synthesis of biocompatible plasmonic nanostructures using embelin and their potential use as antibacterial, CT imaging, and photothermal agents.