Colloidal dispersions of gold rods characterized by dynamic light scattering and electrophoresis

The colloidal stability of nearly monodisperse aqueous dispersions of rod-shaped gold particles is studied by dynamic light scattering and electrophoresis. The average length of the gold particles is adjusted between 39 and 730 nm, and the diameter is about 17 nm. The translational diffusion coefficients are consistent with calculations for single nonaggregated rods with a 10-15 nm thick poly(vinyl pyrrolidone) (PVP) adsorption layer. This supports the colloidal stability observed. Electrophoresis measurements show that the PVP-stabilized gold rods are negatively charged with a zeta potential of about -47 mV, which according to interaction calculations is sufficient for double-layer stabilization. Gold-sphere dispersions are investigated for comparison. It turns out that PVP-stabilized gold spheres have a zeta potential similar to that of the colloidal rods.