Dynamic Light Scattering (DLS) is a standard time tested method for sizing dispersions of nanoparticles. It is the only optical particle sizing technique that can reliably size particles below 10 nanometers.
Figure A illustrates this capability. The PSD in this figure is from a commercial Buckminster Fullerence (C60) or Bucky-Ball suspension. C60 has a reported size in the literature of 14 Angstroms or 1.4 nanometers. The PSD consists of single peak that has a mean diameter of 1.3 nm, very close to the expected value. As a further demonstration of the unique capabilities of DLS, the Figure B contains a PSD from a different lot of the same C60. Notice the presence of a second peak at 200 nm. This peak is likely from amphorous carbon contamination from the synthesis process. DLS was able to sort out the primary peak at the correct size as well as detect the contamination peak.