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 NOx 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.