Monitoring gold nanorod synthesis on surfaces

We describe a simplified method for the synthesis of gold nanorods on surfaces. Gold colloid seeds were deposited by electrostatic attraction onto silicon wafers and grown in a HAuCl4 solution by surfactant-assisted, seed-mediated synthesis. Microscopic analysis of the nanoparticle ensemble allowed direct observation of several aspects of the anisotropic growth of gold nanorods. Individual seed particles were observed to produce individual nanorods,with yields similar to those of previous reports with the seed particles in solution. A minimum seed diameter of 17 nm was required for nanorod nucleation, and this minimum was the same for surfactants with both 12- and 16-carbon chains. However, the chain length affected the isometric seed growth rate, which was faster for the shorter chain surfactant. Altering the surfactant headgroup disrupted the growth anisotropy and produced no nanorods.