Faculty of Mathematics, Physics and Informatics, Comenius University Bratislava |
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Chemical and antibacterial effects of plasma activated water: correlation with gaseous and aqueous reactive oxygen and nitrogen species, plasma sources and air flow conditionsMachala Z., Tarabová B., Sersenová D., Janda M., Hensel K. |
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Abstract: Cold atmospheric plasma operating in contact with water and biological media induce antimicrobial or antitumor effects and represent a great potential for applications in biomedicine and agriculture. The need of control and tunability of the chemical composition and biomedical effects of plasma activated water/media (PAW/PAM) is emerging. By comparing two non-thermal air plasma sources: streamer corona and transient spark, interacting with water in open and closed reactors and by enhancing the plasma-liquid interaction by water electrospray through these discharges, we demonstrate that the plasma gaseous products strongly depend on the discharge regime, its deposited power and gas flow conditions. Streamer corona leads dominantly to the formation of ozone and hydrogen peroxide, while more energetic transient spark leads to nitrogen oxides and hydrogen peroxide. The gaseous products then determine the chemical properties of the PAW and the dominant aqueous reactive oxygen and nitrogen species (RONS). Production of hydrogen peroxide depends on water evaporation and hydroxyl radical formation that is determined by the discharge power. Transient spark produces higher concentrations of gaseous and aqueous RONS and induces stronger antibacterial effects than streamer corona; however, the RONS production rates per Joule of deposited energy are comparable for both studied discharge regimes. The net production rate per Joule of gaseous nitrogen oxides strongly correlates with that of aqueous nitrites and nitrates. Antibacterial effects of the PAW tested on E. coli bacteria are determined by the aqueous RONS: in the lower power streamer corona mainly by the dissolved ozone and hydrogen peroxide, in the higher power transient spark by the combination of hydrogen peroxide, nitrite and acidic pH, while in transient spark in the closed reactor by acidified nitrites.
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