Effects of Gas Flow Rate on Supply of Reactive Oxygen Species Into a Target Through Liquid Layer in Cold Plasma Jet

Understanding the mechanisms for the supply of reactive oxygen species (ROS) into a target through a thin liquid layer by cold plasma jets is essential in biomedical applications. In this paper, impacts of gas flow rate on ROS supply into the liquid bottom were investigated using a KI-starch reagent that can be employed as an ROS indicator even in liquids. ROS distribution visualized on the regent at the liquid bottom was discussed from the stand point of liquid flows induced by the plasma jet irradiation. In the cases of lower gas flow rates, ROS were dominantly transported into the liquid bottom by the plasma-induced linear flow going in the depth direction, and were radially distributed at the bottom. On the other hand, in the cases of higher gas flow rates, ROS were dominantly transported by the supplied-gas-induced vortex flow spreading in the radial direction, and doughnut-shaped ROS distribution patterns were observed at the liquid bottom. The ROS supply into a target through a liquid layer markedly depended on the magnitude relationship between two flows; the vortex flow and the linear flow.