Leaf extracts of two plants, Magnolia kobus and Diopyros kaki, were used for ecofriendly extracellular synthesis of metallic gold nanoparticles. Stable gold nanoparticles were formed by treating an aqueous HAuCl(4) solution using the plant leaf extracts as reducing agents. UV-visible spectroscopy was used for quantification of gold nanoparticle synthesis. Only a few minutes were required for >90% conversion to gold nanoparticles at a reaction temperature of 95 degrees C. suggesting reaction rates higher or comparable to those of nanoparticle synthesis by chemical methods. The synthesized gold nanoparticles were characterized with inductively coupled plasma spectrometry (ICP), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and particle analysis using a particle analyzer. SEM and TEM images showed that a mixture of plate (triangles, pentagons, and hexagons) and spherical structures (size, 5-300 nm) were formed at lower temperatures and leaf broth concentrations, while smaller spherical shapes were obtained at higher temperatures and leaf broth concentrations. (C) 2009 Elsevier Ltd. All rights reserved.