A method of synthesizing highly monodispersed Au nanoparticles having diameters in the range of 30-90 nm. Seed nanoparticles in a controlled concentration are combined with a precursor, also in a controlled concentration, a reducing and capping agent (e.g., sodium acrylate) in aqueous solution. Under controlled conditions of pH, temperature, and time, highly monodispersed nanoparticles having diameters in the range of 30-100 nm are produced. A relative size standard deviation of the size distribution of the resulting nanoparticles is as low as 2%.