During the phase of dust nucleation in plasma enhanced chemical vapor deposition systems, nanometer-sized dust particles appear in large concentrations. The dispersion characteristics of dust acoustic waves in such a plasma during the nucleation phase is analyzed. It is shown that the dispersion properties of the dust acoustic wave depend sensitively on the particle size. It is proposed to use dust acoustic waves as a novel particle size diagnostic for nanometer-sized particles. ©1997 American Institute of Physics.