Exposure to light is a key parameter that influences the chemical interactions and microbial stress of engineered nanomaterials (ENMs). Yet, the photochemistry and phototoxic stress responses of many ENMs and ENM mixtures have not been adequately detailed. We exposed E. coli bacteria to binary combinations of n-TiO2 (a stable metal oxide) with different plasmonic metal ENMs (n-Ag, n-Au, or n-Pt) in a natural aqueous medium under light and dark conditions. Using ATP level and cell membrane integrity probes, we measure the toxic stress due to these ENM mixtures. We previously found that under dark conditions, n-TiO2 attenuates the toxic stress due to low concentrations of n-Ag (<20 μg L-1) via adsorption of Ag+. However, mixtures containing n-Au or n-Pt produce no difference in toxic stress responses with and without n-TiO2 in the dark. In contrast, under simulated solar irradiation, we observed that n-Ag, n-Au, and n-Pt each with n-TiO2 cause synergistic toxic stress. The n-Ag/n-TiO2 combination causes the greatest phototoxicity, followed by n-Au/n-TiO2 and then n-Pt/n-TiO2. Measurements of photocatalytic production of reactive oxygen species reveal that irradiation of n-Ag or n-Au with n-TiO2 yields synergistic production of superoxide anion and hydrogen peroxide. The photochemical interactions of these ENMs, governed by metal ENM solubility and localized surface plasmon resonance, provide mechanistic insight into the amplified photoactivity of mixtures.
ASJC Scopus subject areas
- Materials Science (miscellaneous)
- Environmental Science(all)