Depth Profile Dynamics of Hydrogen Peroxide (H2O2) Decomposition in Phosphate-Buffered Saline (PBS) Solution Exposed to Plasmas-A Numerical Simulation Study

When atmospheric-pressure plasmas (APPs) are applied to living mammalian cells, which typically coexist with saline, the cells may be exposed to various bactericidal agents, including hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>), generated by the plasmas, and possibly protected from bacterial infections. However, an earlier study demonstrated that H<sub>2</sub>O<sub>2</sub> was decomposed in a phosphate-buffered saline (PBS) solution exposed to APPs. In other words, the bactericidal effect of H<sub>2</sub>O<sub>2</sub> may be mitigated under such conditions. The decomposition was attributed to the liquid-phase reaction between H<sub>2</sub>O<sub>2</sub> and hypochlorite anion (ClO<sup>-</sup>). A more recent study has also shown, using global simulations of a liquid-phase chemical reaction model, that chlorine monoxide ClO, rather than ClO<sup>-</sup> , decomposes H<sub>2</sub>O<sub>2</sub> more efficiently in a PBS solution exposed to APPs, although the generation of ClO is required for the presence of ClO<sup>-</sup> . A question, however, remained as to whether the H<sub>2</sub>O<sub>2</sub> decomposition by ClO occurs only near the solution surface or in the solution bulk because a global simulation cannot distinguish the location of chemical reactions inside a solution. The present study is motivated to provide a better understanding of the H<sub>2</sub>O<sub>2</sub> decomposition mechanism. The present study has demonstrated, using one-dimensional numerical simulations, that the reaction between H<sub>2</sub>O<sub>2</sub> and ClO is indeed the dominant decomposition pathway for H<sub>2</sub>O<sub>2</sub> even in the presence of diffusion of chemical species into the solution bulk, and the location of the dominant H<sub>2</sub>O<sub>2</sub> decomposition reaction is not limited to the solution surface region; it can also occur in the bulk of the PBS solution.