Aqueous Reactive Oxygen Species Induced by He + O2 Plasmas: Chemistry Pathways and Dosage Control Approaches

Abstract

Plasma–liquid interaction has already been a hotspot in the research field of plasma medicine. Aqueous reactive oxygen species (ROS) generated in this process are widely accepted playing a crucial role in plasma biomedical effects. In this paper, chemistry pathways among various aqueous ROS induced by He + O2 plasmas are investigated by a numerical model. Simulation results show that these aqueous ROS can be classified into two groups according to their production ways: the group of species including O, 1O2 and e directly produced in plasma, and the other group of species including O2 −, H2O2, O3, etc. produced by liquid reactions. A key reaction chain of e → O2 − → HO2(→ HO2 −) → H2O2 is found to be important in the plasma-induced liquid chemistry. Furthermore, impacts of changes in plasma and solution conditions on aqueous ROS concentrations are studied as well. It is found that changes in plasma conditions (O2 ratio in the discharge gas/power density) can globally influence the concentrations of almost every aqueous ROS, while conditions changes of the treated liquid (pH/dissolved oxygen) only partially influence the concentrations of some specific species including O2 −/HO2, O3 −/HO3 and H2O2. The revelations of the liquid chemistry pathways and the dependence of ROS dosage on the treatment conditions offer a better understanding on the plasma–liquid interactions, as well as provide optimized dosage control approaches for biomedical applications.