Surface air discharge has been extensively reported to have strong antibacterial and anticancer effects, and these biological effects are more or less attributed to the short-lived aqueous reactive species produced by the air plasma. Insight into the generation mechanism for short-lived species is a key bottleneck in elucidating the antimicrobial and anticancer effects. Although the numerical study has predicted that the dissolution of gaseous NO3 plays a crucial role, but so far without experimental validation. In view of this, cavity ring-down spectroscopy is adopted in this paper to measure the NO3 spatial distribution between the surface air discharge and the solutions to be treated, and the concentrations of short-lived species in the solutions after plasma treatment are also measured for different discharge modes. A simplified chemical pathway for the conversion of gaseous NO3 to aqueous ONOOaq
−/ONOOHaq and O2aq
− is proposed. Moreover, the inactivation effects for Escherichia coli and A549 lung cancer cells treated by the plasma-activated solutions are measured for different concentrations of short-lived species, and the key species for sterilization and anticancer are identified by chemical scavengers. Finally, a positive correlation chain is found among the inactivation effect, the concentrations of aqueous ONOOaq
−/ONOOHaq and O2aq
−, and the density of gaseous NO3, implying that NO3 might be very important for the production of aqueous short-lived reactive species as well as the biological effects induced by plasma-activated solutions.
Systemic infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are life-threatening due to their strong multidrug resistance, especially since the biofilms formed by MRSA are more difficult to inactivate by antibiotics, causing long term recurrence of infection. Plasma-activated saline (PAS), a derived form of cold atmospheric-pressure plasma, can effectively inactivate bacteria and cancer cells and has been applied to sterilization and cancer treatment. Previous studies have demonstrated that the pretreatment of MRSA with PAS could promote the action of antibiotics. Here, the PAS was used as an antibiotic adjuvant to promote the inactivation of MRSA biofilms by rifampicin and vancomycin, and the combined treatment reduced approximately 6.0-log10 MRSA cells in biofilms. The plasma-activated saline and rifampicin synergistically and effectively reduced the systemic infection in the murine model. The histochemical analysis and the blood hematological and biochemical test demonstrated that the combined treatment with plasma-activated saline and rifampicin improved the blood hematological and biochemical parameters of infected mice by reducing the infection. Therefore, PAS based on plasma technology represents a new strategy for the treatment of infectious disease caused by multidrug-resistant bacteria and alleviating antibiotic resistance.
Plasma-activated water (PAW), as a derivative of cold atmospheric pressure plasma, can inactivate bacteria and greatly expand the application of plasma technology. Commonly used PAW is activated by a plasma device, plasma jet, or surface discharge plasma. PAW prepared by some methods, such as a plasma jet with low frequency, exhibits little bactericidal effect and cannot be applied for use in disinfection or sterilization. Therefore, developing strategies to improve the bactericidal effects of PAW is necessary. Here, the air was first activated by a surface discharge device with a ceramic dielectric under two modes—the ozone mode and nitrogen oxide mode—and then incorporated with helium as the working gas for the plasma jet, which was used to prepare the plasma-activated saline (PAS). The concentrations of long-lived NO2
− and NO3
− and the short-lived 1O2 in the PAS activated by the nitrogen oxide mode and plasma jet were highest. The amount of ONOO− in the PAS activated by the combination was lower than the amount in the PAS activated only by the plasma jet. The PAS activated by the combination of nitrogen oxide mode and plasma jet exhibited the strongest bactericidal effect, which was consistent with the intracellular reactive oxygen species levels. The scavenger analysis demonstrated that 1O2 and ONOO− play essential roles in bacterial inactivation. These results indicate a new strategy for the preparation of PAW with strong bactericidal ability for application in environmental disinfection.
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