Microwave-assisted rapid facile "Green" synthesis of uniform silver nanoparticles: Self-assembly into multilayered films and their optical properties

We report an environmentally benign process for the synthesis of nearly monodisperse silver nanoparticles in large quantities via a microwave-assisted "green" chemistry method in an aqueous system, using basic amino acids, such as L-lysine or L-arginine, as reducing agents and soluble starch as a protecting agent. The presence of amino acids with basicity such as L-lysine or L-arginine, having two amino groups in each molecule, is indispensable for the synthesis of uniform silver nanoparticles. The current synthetic process can be readily applied to large-scale production, for example, a reaction yielding 0.1 g of nearly monodisperse silver nanoparticles can be performed in a 80 mL microwave sealed vessel. This combination of solvent, renewable reactants, and microwave irradiation seem to make it clear that green chemical synthesis of metal nanoparticles with well-controlled shapes, sizes, and structures has practical potential. Self-assembly of starch-capped silver nanoparticles results in multilayered mirrorlike films forming on the glass slide surface. The surface plasmon transmission of the films has blue-shifted with decreasing silver atom concentrations of the films. The silver films offer great surface enhancement for 4-mercaptobenzoic acid (4-MBA) molecules, and the surface enhancement factor can be efficiently changed by the silver atom concentrations of the films.