Comparison of plasma-activated saline prepared with plasma gases with different N₂/O₂ ratios activated by gliding arc discharge

Methicillin-resistant Staphylococcus aureus (MRSA) presents a significant threat due to the multiple resistance to antibiotics, leading to severe and challenging-to-treat infections. Plasma-activated saline (PAS) prepared by plasma gases, could efficiently inactivate various pathogenic bacteria including both sensitive and antibiotic-resistant bacteria. In this study, the PAS was prepared by plasma gases with different ratios of N₂ and O₂ activated by gliding arc discharge. First, the gaseous reactive species in the plasma gases were compared, revealing that the highest levels of NO _x including NO₂ and N₂O₅ were generated in the gases with the N₂/O₂ ratios of 4:6, 5:5, and 6:4. Subsequently, the PAS prepared by the two plasma-activated gases at the N₂/O₂ ratios of 5:5 and 6:4 exhibited the strongest inactivation effects on both planktic MRSA and biofilms. Furthermore, the aqueous reactive species in the PAS exhibited varied change trends with the increasing N₂/O₂ ratios. Additionally, ultraviolet spectroscopy combined with the probe of N, N-diethyl-p-phenylenediamine was applied for the detection of O₂NOO⁻ in the PAS, and the levels of O₂NOO⁻ in the PAS were positively correlated with the inactivation effects. Moreover, the PAS induced varying levels of nitration modification on the soluble proteins in MRSA cells, which were related to the intensities of O₂NOO⁻ in the PAS. This study regulated the reactive species in the PAS through gas composition and explored the inactivation mechanism of the PAS, providing a new strategy to promote the preparation efficiency of plasma-activated solutions for biomedical applications.