Division of Environmental Physics -
Students Faculty of Mathematics, Physics and Informatics, Comenius University Bratislava
Barbora TARABOVÁ PhD. student
PhD. study 2013 - 2018
Supervisor: Zdenko Machala Title: Plasma activated water: chemical analysis of reactive species and antimicrobial effects Abstract:
MSc. study 2010 - 2012
Supervisor: Zdenko Machala Title:
Abstract: In this Master thesis we investigated bio-decontamination effects of cold non-equilibrium plasma generated by transient spark discharge in air at atmospheric pressure and chemical changes that were induced by the plasma affecting the water bacterial suspensions. We used a model organism - Gram negative (G-) Escherichia coli bacterial cells that formed a suspension in non-buffered aqueous solutions – saline solution and water (solution of NaH2PO4.2 H2O) with different conductivities. In both cases, we observed 100% decontamination effect 5 hours after plasma treatments. In these solutions, we observed a significant decrease in pH ~ 3 and an increase in conductivity. These chemical changes are caused by the formation of peroxides, nitrites NO2ˉ and nitrates NO3ˉ in water. For comparison, we have also worked with bacterial suspensions prepared in the buffers. We used phosphate buffer (PB) Na2HPO4.2 H2O + KH2PO4 and the same PB in saline solution (PBS). The observed decontamination effect was ~ 2 log immediately after treatment and ~ 4 log 5 hours later. At the same time there was no significant decrease in pH, indicating that the rate of decontamination is associated with the acidification of solutions. Non-equilibrium plasma in the presence of water vapor or water is a rich source of reactive species derived from oxygen (ROS) and nitrogen (RNS), which are responsible for oxidative cell damage and subsequent decontamination. The extent of oxidative damage was evaluated by the concentration c(TBARS) - thiobarbituric acid reactive substances. We found an increased degree of oxidative damage of bacteria in non-buffered aqueous solutions, in which high decontamination was observed. We observed the presence of hydrogen peroxide H2O2 and peroxynitrite ONOO ˉ as reactive species. We detected their increased presence in non-buffered aqueous solutions. They are probably responsible for the oxidative damage and a high decontamination rate in these solutions.