You will get answers in here that you can't. Nonetheless if the np are close to spherical and protected with PEG you can run centrifugation and they will not agglomerate.
Interfacial attraction forces "van der Waal's forces may cause agglomeration/aggregation of nanoparticles. You must to disperse your nanoparticles in a medium that reduces the interfacial attraction forces and increases the electrostatic repulsion between them. This can be performed by dispersing nanoprticles with suitable surfactant like PEG,CTAB, SDS, AOT, and assist by ultrasonication.