My particles have a 300-350 nm size, when I use a 20000 G centrifugation in 60 minutes, I noticed that a pellet is formed in the botton but a turbid supernatant too. Does it mean that I still having nanoparticles in supernatant?
It is possible that supernatant has nanoparticles, or just other chemicals like oxidant and surfactant used for polymerization. You could seperate the supernatant and centrifuge it again to clear your doubts. Alternatively, you can also try to find a solvent where the chemicals are soluble but the polymeric nanoparticles are not.