Nanotechnology is a scientific and engineering technology conducted at the nano-scale, such as in the fields of compound fabric manufacturing, food processing, agricultural processing, and engineering, as well as in medical and medicinal applications. In recent decade, nanomaterial applications for antimicrobial works have of prime interest of by many researchers. Available reports show that some of the metal oxide nanoparticles (NPs) including Al2O3, TiO2, ZnO, CuO, Co3O4, In2O3, MgO, SiO2, ZrO2, Cr2O3, Ni2O3, Mn2O3, CoO, and Nickel oxide have toxicity toward several microorganisms and they could successfully kill numerous bacteria. Based on our literature review there are some effective factors that can influence the ability of nanomaterials in reducing or killing the cells, and there are mechanisms for nanomaterial against bacteria, which are briefly listed as follows: surface charge of the metal nanomaterial, shape, type and material, concentration of nanomaterial, dispersion and contact of nanomaterial to the bacterial cell, presence of active oxygen, liberation of antimicrobial ions, medium components and pH, physicochemical properties, specific surface-area-to-volume ratios, size, role of growth rate, role of biofilm formation, cell wall of bacteria, and effect of UV illumination. It can be considered that in the use of nanomaterials as antimicrobial agents, consideration of many factors remain principal. Antibacterial resistance to common chemical antibacterial agents can be due to long production-consumption cycle, thereby reducing their efficiency, and use of poor quality or fake medicines in undeveloped and developing countries. NPs as antimicrobial agents have become an emerging approach against this challenge, which can establish an effective nanostructure to deliver the antimicrobial agents for targeting the bacterial community efficiently. In addition, they are so potent that microbial pathogens cannot develop resistance to wards them. On the other hand, most of the metal oxide NPs have no toxicity toward humans at effective concentrations used to kill bacterial cells, which thus becomes an advantage for using them in a full scale. However, over the present decade, several studies have suggested that NPs are excellent antibacterial agents, at least at the research level.
