Other nanoparticles, such as platinum, gold, iron oxide, silica and its oxides, and nickel have not shown bactericidal effects in studies with bacteria . Yoon et al. reported the antibacterial effects of silver and copper nanoparticles using single representative strains of E. coli and Bacillus subtilis, where the copper nanoparticles demonstrated superior antibacterial activity compared to the silver nanoparticles.