Disclosed is a method for making a colloidal suspension of precious metal nanoparticles. The method comprises providing a target material comprising a precious metal in a liquid dispersion medium in an ablation container. The dispersion medium has an electrical conductivity within a predetermined conductivity range. Laser pulses are used to generate the nanoparticles from the target in the container. While generating the nanoparticles the electrical conductivity of the dispersion medium is monitored and maintained within the predetermined range and thereby the generated nanoparticles are produced within a predetermined size range. The generated nanoparticles are used to form a colloidal suspension.