We're using standard DLS (dynamic light scattering) equipment (Malvern Zetasizer). Please be aware that e.g. viscocity measurements for nanofluids are not reliable.
Note added: If the particle size distribution is not very sharp, or if there are multiple peaks in it the DLS data may be unrelaible. It's always a good idea to check the results using a real-space probe, such as TEM with cryostat-frozen samples.