Transportation of ROS in model tissues treated by an Ar + O₂ plasma jet

The transportation of reactive oxygen species (ROS) in model tissues treated by an Ar + O₂ plasma jet was investigated in this paper. Gelatin gel was used to make the model tissues, and KI-starch reagent was used as an indicator of ROS including O₃, O and HO₂. It was found that the transportation of ROS covered almost the whole surface of the model tissue with good uniformity, despite the small size of the plasma jet source. The center part of the model tissue was almost undyed, of which the area increased slightly with the gas flow rate. The surface pattern of ROS moved downwards with the inclination angle of plasma irradiation, because the molecular weight of argon is larger than that of air. This downward trend could be stopped by adding a certain amount of helium into the Ar + O₂ plasma jet, which is beneficial to precisely control the effective treatment area in clinical applications. Moreover, the dependence of the penetration depth of O₃ on the plasma treatment time or the water content of model tissues was formulated, with a similar trend but lower penetration speed than that of the He + O₂ plasma jet as reported previously.