Synthesis, characterization and antibacterial mechanism study of small water-soluble iron-doped zinc oxide nanoparticles

Inorganic antimicrobial materials have the advantages of high safety, strong durability, stable antimicrobial performance, and good heat resistance compared with organic antimicrobial materials. In this study, Fe-doped small zinc oxide nanoparticles (FZO-NPs) with different iron contents were synthesized and then modified with 3-aminopropyltriethoxysilane (APTES) and poly(ethylene glycol)-600 (PEG-600) to afford FZO-APs. FZO-APs which were fully characterized can disperse in water with good dispersity and improved stability. In antimicrobial tests, FZO-AP4 displayed excellent antimicrobial effects under 10 min of 365 nm UV light against Gram-negative bacteria Escherichia coli (E. coli) and Gram-positive bacteria Staphylococcus aureus (S. aureus) with a minimum inhibitory concentration (MIC) of 0.20 and 0.15 mg/mL, respectively. The antimicrobial mechanism studies revealed that the consumption of glutathione (GSH) and ascorbic acid (ASA), and the generation of reactive oxygen species (ROS) could trigger lipid peroxidation (LPO) and ultimately induce ferroptosis in bacterial cells. The cause of the cell wall/membrane damage and the released Zn/Fe ions from the nanoparticles inside the bacterial cells further promote the antimicrobial effects. In addition, FZO-AP4 showed high inhibitory effects on bacterial biofilm formation and significantly disrupted the formed biofilm. Interestingly, higher bacterial biofilm residuals and bacterial survival were found in E. coli than in S. aureus after FZO-AP4 treatment, suggesting a potential link between the quorum sensing (QS) system of the bacteria and their different susceptibility towards FZO-AP4. This study proved the antibacterial effects of small water-soluble FZO-APs which is meaningful for the design and development of new inorganic nano-material for antimicrobial applications.