Effects of •OH and •NO radicals in the aqueous phase on H ₂ O ₂ and NO 2 − generated in plasma-activated medium

A plasma-activated medium (PAM), which means a cell-culture medium irradiated with cold atmospheric plasmas or non-equilibrium atmospheric pressure plasma (NEAPP), has shown strong antitumor effects on various kinds of cells such as gastric cancer cells, human lung adenocarcinoma cells, human breast cancer cells and so on. In order to clarify the mechanism, it is extremely important to investigate the behaviors of stable and unstable reactive oxygen nitrogen species in culture medium irradiated by NEAPP. The roles of hydroxyl radicals (•OH) and nitric oxide (•NO) were studied to understand the dominant synthetic pathways of H 2 O 2 and NO 2 − in culture medium irradiated with NEAPP. In the PAM, •OH in the aqueous phase was generated predominantly by photo-dissociation. However, most of the H 2 O 2 nor NO 2 − generated in the PAM did not originate from aqueous •OH and •NO. Pathways for the generation of H 2 O 2 and NO 2 − are suggested based on the high concentrations of intermediates generated at the gas/aqueous-phase interface following NEAPP irradiation. On the basis of these results, the reaction model of chemical species in the culture medium is proposed.