Escherichia coli fatality dependence on oxidation level of graphite: Insights into membrane permeabilization and protein leakage.

• Graphene oxide (GO) with various oxidation levels were prepared and characterized. • Highly oxidized GO induced high antibacterial efficacy, with an IC50 value of 161 µg mL⁻¹. • IC50 negatively correlated with GO's oxidization level. • Highly oxidized GO caused bacteria membrane rupture, protein leakage, and fatality. Graphene oxide (GO) with different oxidation levels were evaluated for their bactericidal activities, with the aim to investigate the antibacterial mechanism by correlating the bactericidal efficacy with GO oxidation level. The GO samples were synthesized and labelled as GO1, GO2, GO3 and GO4 using graphite/KMnO 4 ratios of 1:3, 1:4, 1:5 and 1:6, respectively. Those samples were characterized and tested for antibacterial activity against Escherichia coli (E. coli). This study revealed graphite transformation from multilayer stacks to monolayer wrinkled GO nanosheets with increasing KMnO 4 dosage. The higher oxidized GO exhibited a lower negative zeta potential value, and higher O/C ratio. GO4 exhibited the lowest half maximal inhibitory concentration value at 161 µg mL⁻¹, followed by GO3 (307 µg mL⁻¹), GO2 (652 µg mL⁻¹), and GO1 (1077 µg mL⁻¹), indicating a strong correlation (R²=0.94) between oxidation level and bactericidal effectiveness. GO primarily interacts with the outer membrane through its hydrophobic surface, leading to permeabilized membrane (˃ 50 %), protein leakage (˃ 40 µg mg⁻¹), significant morphological alterations, triggering reactive oxygen species production, and resulting in extensive damage to the entire bacterial cell. In summary, highly oxidized GO4 (O/C ratio of 0.54) demonstrated antibacterial potential for clinical use. [Display omitted] [ABSTRACT FROM AUTHOR]