GNP dispersions were prepared using a bath-type sonication method. Since they do not disperse in water without a surfactant, GNPs (1 and 5 wt.%) were dispersed in 2-propanol (IPA) and deionized water (DI) (50% propanol + 50% water) to prepare a homogeneous dispersion. Firstly, the GNP, IPA, and DI water were mixed using a magnetic stirrer for 2 hours. Then, the GNP dispersion was sonicated in a bath sonicator for 2 hours to achieve a homogeneous dispersion.