Aqueous Reactive Species Induced by Dielectric Barrier Discharge Plasma in Pure Water: A Quantitative Study

This study quantitatively examined the generation dynamics of reactive oxygen and nitrogen species (RONS) in low-temperature plasma-activated pure water using a dielectric barrier discharge (DBD) system under different gas atmospheres (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{N}_{2}$</tex>, air, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{O}_{2}$</tex>). By systematically adjusting plasma discharge power (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5-15 ~\mathrm{W}$</tex>) and treatment duration (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0-60 ~\mathrm{s}$</tex>), combined with spectrophotometric and fluorometric assays, we characterized the concentration profiles of nitrate <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\left(\text{NO}_{3}{ }^{-}\right)$</tex>, nitrite (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{NO}_{2}^{-}$</tex>), and hydrogen peroxide (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{H}_{2} \mathrm{O}_{2}$</tex>), while monitoring pH stability. Key findings include: (1) During the plasma treatment process, the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{~ p H}$</tex> of PBS remained relatively stable, with a change greater than 2. Such a drastic <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{p H}$</tex> shift may not be suitable for the treatment of living cells; (2) Nitrogendominated atmospheres (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\approx \text{8 0 \%} \mathrm{N}_{\mathrm{2}}$</tex> content) substantially enhance reactive nitrogen species production. These findings underscore the importance of gas-phase chemistry in tailoring RONS composition and highlight the need for further mechanistic studies on short-lived RONS (e.g., <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\cdot \text{OH}, \text{ONOO}^{-}$</tex>) generation and their spatiotemporal biological effects.