Physical mechanisms of inactivation of Bacillus subtilis spores using cold atmospheric plasmas

This paper presents a detailed study of the potential physical mechanisms of the microbial inactivation by cold atmospheric plasmas. With the Bacillus subtilis spores as a model microorganism and an atmospheric-plasma plume in helium flow, optical emission spectroscopy and inactivation kinetics are used to demonstrate the dominating role played by the reactive oxygen species (e.g., atomic oxygen and OH) as well as the minor contributions of the UV photons, heat, charged particles, and electric fields. To differentiate the concentrations of the reactive oxygen species, an atmospheric helium-oxygen plasma is also used for the spore inactivation. Results with the helium and the helium-oxygen plasmas are contrasted to highlight how the production of the spore-killing oxygen species may be enhanced.