| AVS 66th International Symposium & Exhibition | |
| Plasma Science and Technology Division | Monday Sessions |
| Session PS1-MoA |
| Session: | Plasma-Liquid Interactions, Medicine, and Agriculture |
| Presenter: | Katsuhisa Kitano, Osaka University, Japan |
| Authors: | K. Kitano, Osaka University, Japan S. Ikawa, Osaka Research Institute of Industrial Science and Technology, Japan Y. Nakashima, Osaka Research Institute of Industrial Science and Technology, Japan T. Yokoyama, Osaka University, Japan A. Tani, Kobe University, Japan |
| Correspondent: | Click to Email |
Plasma medicine is one of attractive research areas in the area of plasma application. By the exposure of low temperature atmospheric plasma to living organism (human body, bacteria, and so on), positive effect is expected. As biological environment is wet condition, plasma induced chemical reactions in liquid should be considered.
For the plasma disinfection of human body, we have developed the reduced-pH method with direct plasma exposure, which brings stronger bactericidal activity in the liquid at lower pH condition, where the threshold is pH 4.8. The enhancement is thought to be due to hydroperoxy radical (HOO•) generated from superoxide anion radical (O2–•) by acid dissociation equilibrium (pKa 4.8). Electrically neutral HOO• could easily penetrate into cell to bring intracellular oxidative stress. In addition, we found that the plasma-treated water (PTW) also has strong bactericidal activity under acidic condition in the same manner. Physicochemical properties of PTW are discussed based on chemical kinetics. Lower temperature brings longer half-life, and the bactericidal activity of PTW can be kept by cryo-preservation. This means that PTW with higher bactericidal activity could be obtained by longer plasma treatment under enough low temperature. High performance PTW, corresponding to the disinfection activity of 22 log reduction (against Bacillus subtilis spore), can be obtained by special plasma system equipped with cooling device. The bactericidal activity of our PTW is much stronger than others.
Many researchers are interested in this area of PTW, where the waters are treated / activated by their original devices. For scientific understanding, we should discuss based on chemical species. Although PTW has many chemical components, respective chemical components in PTW were isolated by ion chromatography. Active ingredient of PTW was successfully purified to be confirmed to HOONO2 (PNA: peroxynitric acid). Although the existence of PNA has been known since 100 years ago, sterilization by PNA has never been reported in past papers. PNA is known to release HOO• by radical cleavage. So we conclude that PNA is a key chemical species of cryo-preserved PTW with the reduced-pH method.
From the experimental results of chemical synthesis, PNA is effectively generated from HNO2 and H2O2 under extremely acid condition (pH < 2). Although averaged pH of PTW is about 3~4, pH at the surface of PTW (limited area of interface between plasma and liquid) during plasma treatment is thought to be enough low that PNA can be synthesized from HNO2 and H2O2 supplied from plasma. In the presentation, peroxynitric acid chemistry in PTW will be discussed in detail.