Investigation on the RONS and bactericidal effects induced by He + O2 cold plasma jets: In open air and in an airtight chamber

Abstract

He + O2 plasma jets in open air and in an airtight chamber are comparatively studied, with respect to their production of gaseous/aqueous reactive species and their antibacterial effects. Under the same discharge power, the plasma jet in open air has higher densities of gaseous reactive species and a higher concentration of aqueous H2O2 but lower concentrations of aqueous OH and O2-. In addition, the increase in the O2 ratio in He in both plasma jets causes a linear decrease in the population of gaseous reactive species, except for O(3p5P) when a small amount of O2 is added to the working gas. The concentrations of aqueous reactive species for OH and H2O2 also drop monotonically with the increase in additive O2, while the aqueous O2- first increases and then decreases. Moreover, it is interesting that the bactericidal inactivation in the airtight chamber condition is much greater than that in the open air condition regardless of the presence or absence of additive O2 in the He plasma jet. The concentration trends of O2- for both the plasma jets are similar to their antibacterial effects, and little antibacterial effect is achieved when a scavenger of O2- is used, indicating that O2- should be a main antibacterial agent. Moreover, it should not be O2- alone to achieve the antibacterial effect, and some reactive nitrogen species such as ONOO- and O2NOO- might also play an important role.