Effect of aqueous media on the copper-ion-mediated phototoxicity of CuO nanoparticles toward green fluorescent protein-expressing Escherichia coli

• Effect of aqueous media on phototoxicity of CuO to GFP-E. coli was investigated.
• CuO released different amounts of Cu2+ in four media under UV-365 irradiation.
• Phototoxicity of CuO toward GFP-E. coli followed the order DI>NaCl>PBS>LB.
• CuO toxicity logarithmically increased with Cu2+ amounts (R2>0.90) in each medium.
• Cu2+ leads to cell walls fragmentation, cellular component leakage and cell death.

Quantitative comparison of different aqueous media on the phototoxicity of copper oxide nanoparticles (CuO NPs) is crucial for understanding their ecological effects. In this study, the phototoxicity of CuO NPs toward the green fluorescent protein-expressing Escherichia coli (GFP-E. coli) under UV irradiation (365 nm) was investigated in Luria-Bertani medium (LB), NaCl solution, deionized water (DI) and phosphate-buffered saline (PBS). The phototoxicity of CuO NPs toward GFP-E. coli decreased in the order of DI>NaCl>PBS>LB because of different released concentrations of Cu2+. The 3 h released Cu2+ concentrations by 10 mg/L CuO NPs in DI water, NaCl solution, LB medium, and PBS were 1946.3±75.6, 1242.5±47.6, 1023.4±41.2, and 1162.1±41.9 μg/L, respectively. Transmission electron microscope and laser scanning confocal microscope images of E. coli exposed to CuO NPs demonstrated that the released Cu2+ resulted in fragmentation of bacterial cell walls, leakage of intracellular components, and finally death of bacteria in four media after UV light irradiation. In each medium, the bacterial mortality rate logarithmically increased with the releasing concentrations of Cu2+ by CuO NPs (R2>0.90) exposed to 3 h UV light. This study highlights the importance of taking into consideration of water chemistry when the phototoxicity of CuO NPs is assessed in nanotoxicity research.

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