Rapid, One-Pot, Protein-Mediated Green Synthesis of Gold Nanostars for Computed Tomographic Imaging and Photothermal Therapy of Cancer

Plasmonic nanostructures such as gold nanostars have immense prospects in the biomedical field. However, toxic precursors and complex methodologies of synthesis are the major obstacles to their application. This study hence makes use of a protein macromolecule (albumin) to synthesize gold nanostars by a simple reduction method. The formation of an anisotropic morphology of gold using albumin was determined to be a pH-dependent process. The net positive charge of the protein at pH below its isoelectric point facilitated the attachment of chloroaurate ions, which were subsequently reduced to gold atoms. Furthermore, the stretching of the α-helices of albumin at low pH and its transformation to the β-sheet conformer favored the oriented growth of the gold nanostructures to yield a star-shaped morphology. Additionally, the non-toxic and ligand binding characteristics of the albumin endowed the gold nanostars with stability, functionality, as well as biocompatibility. The albumin-derived gold nanostars exhibited enhanced computed tomographic (CT) contrast, photothermal activity, and compatibility toward cells and human blood. This study thus puts forth, for the first time, a rapid, one-pot methodology for developing gold nanostars using protein and demonstrates the application of the resulting gold nanostars as a dual CT diagnostic and photothermal therapeutic agent.