Methods
Polystyrene nanoparticles (PS NPs) were fabricated from an emulsion of PS/toluene in water using several surfactants, and purified via dialysis in a simple procedure. The synthesis process was carried out at room temperature, without hazardous chemicals, and with a workload of 5 h. All relevant parameters–surfactant type, component concentration, solvent volume, polymer chain length, sonication time–were varied and the effect on the size of the resulting PS NPs were determined. A robust PS NP synthesis procedure was developed, repeated, and tested by three independent researches. The procedure was up-scaled to prove the applicability of the method and the NPs were prepared with four different hydrophobic dyes.

Results
All products were found to be comparable, and we conclude that the method can provide PS NPs with or without dye dopants with an average diameter of 25 nm in a reproducible size distribution.