Methods for preparing aqueous suspension of precious metal nanoparticles

A colloidal suspension comprising;

• precious metal nanoparticles selected from the group consisting of gold, silver, copper, platinum, palladium, rhodium, ruthenium, iridium, osmium, and an alloy including at least one of said precious metals, said nanoparticles having a size distribution including a single peak and a size range of from about 1 to 100 nm, said nanoparticles being at a molar particle concentration of more than 0.01 nM in a suspension liquid, said suspension liquid being free from any nanoparticle dispersants, stabilizing agents, or surfactants that cause steric repulsion between said nanoparticles other than at least one added predetermined electrolyte, said added predetermined electrolyte consisting essentially of at least one anion or cation formed with an element selected from the group consisting of the alkali metal elements from Group 1 of the Periodic Table, the alkaline earth metal elements from Group 2 of the Periodic Table, and the halide elements from Group 17 of the Periodic Table, wherein an electrical conductivity of said suspension liquid is stabilized by the addition of said predetermined electrolyte, and
• wherein the amount of the predetermined electrolyte added is selected to cause the colloidal suspension to have an initial electrical conductivity of from greater than 2.0 to 25 μS/cm and wherein an increase of said electrical conductivity of said colloidal suspension over time is less than 1.5 μS/cm per week.