Formation of ROS and RNS in Water Electro-Sprayed through Transient Spark Discharge in Air and their Bactericidal Effects

Chemical and bactericidal effects induced by plasma in water upon electro-spraying through DC-driven positive transient spark discharge in air were investigated. Inactivation of E. coli was determined in dependence on pH (controlled by buffers) and correlated with chemical changes induced in water. Productions of hydrogen peroxide, nitrites, nitrates, peroxynitrites, and pH changes were determined, and the extent of oxidative stress induced in bacteria was evaluated. The degree of inactivation and oxidative damage of bacteria increased with the increasing acidity of the solution. Acidified nitrites interacting with hydrogen peroxide were determined as the most important bactericidal ROS/RNS agents in plasma-treated water. A possible role of peroxynitrites, ozone, and metal nanoparticles is discussed.