We further investigated the viability of E. coli cells exposed to different concentrations of MSNs. Fig 3 illustrates that the experimental groups contacted with different dosages of MSNs showed a slight and dose-dependent inhibition of viability. These findings were consistent with other published work, which reported that MoS2 showed mild direct cytotoxicity . In our experiment, E. coli was cultured in aqueous solution in shake flasks and we hypothesized that the low observed toxicity might be attributed to the very low solubility of MSNs.