Changing exposure media can reverse the cytotoxicity of ceria nanoparticles for Escherichia coli

Ceria nanoparticles have attracted a great deal of concern about their impact on human health and the environment due to their widespread applications. In the present work, different exposure media (normal saline and phosphate-buffered saline [PBS]) were used to adjust the surface charge density in order to investigate the influence of surface charge on the cytotoxicity of ceria nanoparticles for Escherichia coli. The results showed that the direct contact mediated by the electrostatic attraction between the cell wall and the positive-charged ceria nanoparticles in normal saline would result in outer membrane destabilization, increased reactive oxygen species (ROS) production and loss of viability. The situation in PBS was totally different, with significantly reduced contacts, so no outer membrane destabilization, no increased ROS production, and no cytotoxicity. The results suggested that surface charge density was closely involved in the cytotoxicity of ceria nanoparticles for E. coli. This work as a well designed comparison study contributes to a better understanding of the charge-associated biological effects of nanomaterials.