二維奈米碳材中包含了石墨烯和氧化石墨烯，其中氧化石墨烯因材料特性及相容性的優勢上，在生醫、電子、環境以及能源等等領域中擁有前瞻性應用而引起了廣大的研究風潮。然而在這些廣泛開發應用前進行環境生態影響評估是非常重要的步驟。在過去研究顯示，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，故本研究目的是對於光照前後的氧化石墨烯其抗菌毒性。藉由透過直接光照與含有氫氧自由基的間接光照的結果中，我們發現格蘭式陰性菌的大腸桿菌(E. coli)對於初始氧化石墨烯的最小抑制濃度(MIC)為5 mg/L及其半數抑制濃度(IC50)為5.03 ± 1.75 mg/L。有趣的是相較於未光照的氧化石墨烯在直接光照具有較強的抗菌毒性，而間接光照反應後的氧化石墨烯顯示相反的毒性結果。探討材料特性變化後，造就毒性增強的可能原因是直接光解的去除部分官能基與/或粒徑變小，而毒性降低則主要歸因於在間接光照下氧化石墨烯質量濃度大幅下降。
此外，本研究也探討氧化石墨烯其抗菌毒性的潛在機制，利用細菌的細胞膜完整性、胞內抗氧化劑穀胱甘肽的耗損、以及活性氧化物質分析。結果顯示氧化石墨烯促使細菌產生明顯聚集現象，暴露直接光照反應後的氧化石墨烯導致細菌外表嚴重變形，更進一步了解發現隨著直接光照時間增加，產生的氧化石墨烯中間產物能夠耗損較多的穀胱甘肽以及產生更多的活性氧化物質。總結各項結果發現光反應後氧化石墨烯抗菌毒性機制之一可能為氧化壓力。簡而言之，本研究顯示環境光化學轉化對於氧化石墨烯的抗菌活性有關鍵的影響。

Two-dimensional carbon-based nanomaterials, including graphene and graphene oxide (GO), have attracted great research interests for their potential applications in biomedical, electronics, energy, and materials areas. Ecological impacts of these materials must be properly evaluated prior to their widespread use. Previous research has shown that GO can be phototransformed under simulated sunlight exposure, forming products with progressively reduced sizes and oxygen-containing functionalities. The aim of this work was to examine the antibacterial toxicity of GO before and after photoreactions. Photoproducts generated by direct photolysis and indirect photolysis in which hydroxyl radical was involved were examined. We found that Gram negative Escherichia coli (E. coli) had a minimum inhibitory concentration (MIC) of 5 mg/L and a half maximal inhibitory concentration (IC50) of 5.03 ± 1.75 mg/L for parent GO. Interestingly, GO derivatives produced by direct photoreduction exhibited stronger antibacterial effects than parent GO, while GO samples after indirect photoreaction showed opposite results (i.e., reduced toxicity). The enhanced toxicity correlates with the reduced functional groups and/or sizes after direct photolysis, while the reduced toxicity may be mainly attributed to the significantly decreased mass concentration after indirect photolysis.
Another part of this research was to evaluate the potential mechanisms behind the observed antibacterial toxicity. The whole cell and membrane integrities, the depletion of glutathione (GSH), an intracellular antioxidant, and reactive oxygen species (ROS) formation were examined. We found that the cell deformation occurred upon exposure to GO samples irradiated for a longer time period under direct photolysis conditions and that bacterial cells strongly aggregated in the presence of GO. The increased cell membrane permeability was observed after exposure to GO. Increased irradiation time period under direct photolysis conditions resulted in intermediate products with greater capabilities in GSH depletion and ROS　formation. Taken together, the results point to the oxidative stress-mediated antibacterial toxicity. Overall the findings of this work indicate that phototransformed GO exhibits different antibacterial toxicity from parent GO.

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