Experimental identification of the reactive oxygen species transported into a liquid by plasma irradiation

Reactive oxygen species (ROS) supplied into liquids by plasma irradiation must be identified and controlled for the safe and effective use of plasmas in biomedical applications. This study aims to obtain information on the key ROS regarding ROS transportation through a liquid layer for realization of spatial ROS identification. Two-dimensional distributions of ROS after passing through liquids with and without ROS scavengers were visualized and compared to assess the suppression effects of each scavenger using a measurement system combined with a gel ROS detector. The plasma was generated under helium and 1% oxygen mixture gases. It was experimentally confirmed that a hydroxyl radical is not a key species, whereas, superoxide anion radicals and hydrogen peroxide play a key role for ROS transportation in our system. The results also suggested that the chemical processes for ROS transportation change at a liquid layer thickness of less than 1 mm.