I want to determine the antibacterial activity of Zinc Oxide nanoparticles by the disc diffusion method. In order to impregnate the disc with the appropriate concentration of ZnO, it has to be diluted (not dissolved) homogeneously. I have used methanol, DCM, and DMSO. I also used sonication and vortex shaking for the homogenization. Nevertheless, the ZnO did not show any antibacterial activity. Can anyone provide me a detailed SOP or procedure and suggest me a suitable solvent? Thanks in advance.