UV–vis spectroscopy study of plasma-activated water: Dependence of the chemical composition on plasma exposure time and treatment distance

Abstract

Plasma-activated water (PAW) is receiving much attention in biomedical applications because of its reported potent bactericidal properties. Reactive oxygen and nitrogen species (RONS) that are generated in water upon plasma exposure are thought to be the key components in PAW that destroy bacterial and cancer cells. In addition to developing applications for PAW, it is also necessary to better understand the RONS chemistry in PAW in order to tailor PAW to achieve a specific biological response. With this in mind, we previously developed a UV–vis spectroscopy method using an automated curve fitting routine to quantify the changes in H₂O₂, NO₂ ⁻, NO₃ ⁻ (the major long-lived RONS in PAW), and O₂ concentrations. A major advantage of UV–vis is that it can take multiple measurements during plasma activation. We used the UV–vis procedure to accurately quantify the changes in the concentrations of these RONS and O₂ in PAW. However, we have not yet provided an in-depth commentary of how we perform the curve fitting procedure or its implications. Therefore, in this study, we provide greater detail of how we use the curve fitting routine to derive the RONS and O₂ concentrations in PAW. PAW was generated by treatment with a helium plasma jet. In addition, we employ UV–vis to study how the plasma jet exposure time and treatment distance affect the RONS chemistry and amount of O₂ dissolved in PAW. We show that the plasma jet exposure time principally affects the total RONS concentration, but not the relative ratios of RONS, whereas the treatment distance affects both the total RONS concentration and the relative RONS concentrations.