石墨烯和氧化石墨稀材料在眾多領域發展應用，對於環境生態的影響必須在廣泛應用前評估。我們過去研究顯示，氧化石墨烯在全幅模擬太陽光下被光逐漸反應成較小且失去含氧官能基的產物，隨著光反應環境的不同，我們發現反應後的氧化石墨烯產物有些抗菌毒性變強，有些毒性消失，惟原因仍不清楚，因此本研究的目的為探討此現象發生的機制。我們藉由抗菌活性、細菌的型態、細胞膜的完整性與抗氧化劑的作用來分析。結果顯示直接光轉化後的氧化石墨稀毒性增加，原因可能是光轉化去除氧化石墨烯部分官能基與/或尺寸變小。大腸桿菌K12暴露於氧化石墨稀及照光的氧化石墨稀，觀察到細胞外表的變形且細胞膜破裂。從抗氧化劑的添加和未添加相比可以減少細菌的失活，由此可之，氧化壓力是參與實驗結果的抗菌活性。

This work examined the mechanism behind the antibacterial activity of graphene oxide (GO) before and after phototransformation in sunlight conditions. Our previous research has shown that GO can be phototransformed under simulated sunlight exposure, forming products with progressively reduced sizes and oxygen-containing functionalities. Depending on the phototransformation conditions, GO could become more toxic, while the toxicity was negated after phototransformation in the presence of H2O2 (i.e., indirect photolysis). While the finding is interesting and could aid in assessing the ecological impact of GO, the mechanism is not completely clear. This is the motivation of this study. New techniques including the antibacterial test of GO materials deposited on surfaces, cell morphology, membrane integrity using fluorescence dyes, and antioxidant effect, and reactive oxygen species (ROS) detection were developed and used to shed mechanistic light on the altered toxicity after phototransformation. The results indicate that bacteria incubated with phototransformed GO deposited on surfaces showed increased growth inhibition. The enhanced toxicity could be attributed to the reduced functional groups and/or sizes of GO after phototransformation. Greater cell deformation and increased membrane permeability correlated with larger extent of GO phototransformation. The growth of bacteria incubated with GO materials and antioxidants including natural organic matter (NOM) increased, indicating that oxidative stress likely plays a role. Collectively, the results indicate that phototransformation enhanced antibacterial activity is associated with oxidative stress that increases with the degree of phototransformation.

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