Synthesis of multiple shaped gold nanoparticles using wet chemical method by different dendritic peptides at room temperature

Abstract

Gold nanoparticles of various shapes including pentagonal, hexagonal, prismatic, branched (multipods), spherical and oval have been prepared by using different generations of peptidic dendrons as templates at room temperature without adding any external reducing or stabilizing agents. Each peptide based dendron molecule (G1, G2 or G3) contains a redox active tyrosine (Tyr) moiety and a free –NH₂group at the N-terminus and as a result of that each peptide-dendron molecule can be used to reduce AuCl₄⁻ to Au⁰ and stabilize the nascent gold nanoparticles (GNPs) by the NH₂group present in the molecule at room temperature. Not only the shapes but also the sizes of these particles can be tuned by using this chemical methodology involving different peptidic dendrons in water-methanol (4:1) at pH 11. The first generation dendritic peptide produces various shaped GNPs, while the second-generation peptide-dendron molecule leads to the exclusive formation of hexagonal gold nanoparticles and the third generation dendritic peptide gives rise to branched nanoparticles at a certain dendron concentration (5.88 × 10⁻⁶ M). In this procedure no external reducing agents or stabilizing agents nor relatively high temperature are required to produce various anisotropic gold nanoparticles. Nanoparticles with different shapes exhibit their characteristic surface plasmon resonance peaks. TEM images vividly demonstrate the specific morphology of gold nanoparticles with different shapes obtained by using different generations of peptide-based dendrons. Corresponding dark field luminescence spectra provide an insight into the shape dependence of the optical properties.