Comparison of toxicity of Fe/Ni and starch-stabilized Fe/Ni nanoparticles toward Escherichia coli

This study examined the toxicities of Fe/Ni and starch-stabilized Fe/Ni (S-Fe/Ni) nanopartides (NPs) toward Escherichia coli. The inactivation of E. coli by Fe/Ni NPs was concentration- and time-dependent. Fe/Ni NPs exhibited a stronger toxicity than the bare Fe-0 NPs (i.e., Ni = 0 wt%), revealing that the loading of Ni increased the toxicity of Fe NPs. However, there was no positive correlation between Ni content and the toxicity of Fe/Ni NPs when Ni content increased from 1 wt% to 5 wt%. The starch coating could alleviate the toxicity of Fe/Ni NPs, depending on starch concentration. Transmission Electron Microscopy analysis demonstrates that membrane disruption and cellular internalization of NPs occurred for E. coli after exposure to the Fe/Ni NPs. The NPs might have reacted with the carboxyl, ester and amine groups on the cell surface, as indicated by the Fourier Transform Infrared Spectroscopy analysis. However, the S-Fe/Ni NPs did not cause obvious membrane disruption of the cells due to the effect of starch coating, which inhibited the close contact of NPs with cells by providing electrostatic repulsion and steric hindrance. Besides, the addition of N-Acetyl-L-cysteine, as a potent scavenger for reactive oxygen species (ROS), remarkably reduced the toxicities of both Fe/Ni and S-Fe/Ni NPs, which indicated that the ROS-induced oxidative stress should be the primary mechanism for the inactivation of E. coli. The aging experiments evidenced that both Fe/Ni and S-Fe/Ni NPs would lose their toxic potential over time, posing less threat to the environment in the long term.