Biodirected Synthesis and Nanostructural Characterization of Anisotropic Gold Nanoparticles

Gold nanoparticles with anisotropic structures have tunable absorption properties and diverse bioapplications as image contrast agents, plasmonics, and therapeutic–diagnostic materials. Amino acids with electrostatically charged side chains possess inner affinity for metal ions. Lysine (Lys) efficiently controlled the growing into star-shape nanoparticles with controlled narrow sizes (30–100 nm) and produced in high yields (85–95%). Anisotropic nanostructures showed tunable absorbance from UV to NIR range, with extraordinary colloidal stability (−26 to −42 mV) and surface-enhanced Raman scattering properties. Advanced electron microscopy characterization through ultra-high-resolution SEM, STEM, and HR-TEM confirmed the size, nanostructure, crystalline structure, and chemical composition. Molecular dynamics simulations revealed that Lys interacted preferentially with Au­(I) through the −COOH group instead of their positive side chains with a binding free energy (BFE) of 3.4 kcal mol<sup>–1</sup>. These highly monodisperse and colloidal stable anisotropic particles prepared with biocompatible compounds may be employed in biomedical applications.