Seeding of colloidal Au nanoparticle solutions. 2. Improved control of particle size and shape

New fields of research in chemistry and physics require improved synthetic techniques for colloidal metal particles. This paper reports a generally applicable technique for synthesizing colloidal Au particles of mean diameters between 20 and 100 nm that exhibit improved monodispersity relative to previously published methods. In this approach (called 'seeding') Au³⁺ is reduced on the surface of preformed 12-nm-diameter Au nanoparticles by introduction of boiling sodium citrate, producing particles highly uniform in size and shape. A similar procedure, utilizing the reductant NH₂OH at room temperature, produces two populations of particles; the larger population is even more spherical than citrate-reduced particles of similar size, while the smaller population is very distinctly rod-shaped.