Inactivation of virus and bacteria using cold atmospheric pressure air plasmas and the role of reactive nitrogen species

Cold atmospheric pressure plasma has potential as a non-thermal processing technology to decontaminate food and food contact surfaces due to its ability to generate an abundance of reactive oxygen and nitrogen species with antimicrobial attributes at ambient conditions. In this study, we present a comparison on the effectiveness of surface decontamination against feline calicivirus (FCV) and Salmonella spp using four different plasma sources, a dielectric barrier discharge (DBD) in direct contact with the substrate and three remote plasma treatment sources: a 2D DBD, a volumetric DBD and a gliding arc discharge. The plasma sources were all operated in air at atmospheric pressure. The decontamination efficacy was enhanced by the presence of humidity on the sample surface and only direct contact between plasma and samples allowed the inactivation of pathogens on dry substrates. Across all sources, FCV was seen to be more susceptible to the plasma-generated species than Salmonella spp. The diminished effectiveness of the gliding arc discharge compared to the DBDs operating at the same power is most likely due to the low Henry's law constant of NO, the dominant reactive species generated by the gliding arc. Control experiments illustrate that the co-existence of O3 and NO2, as in the afterglow of the remote DBDs enhances the inactivation compared to the inactivation by O3 or NO2 only. A chemical kinetics model of the plasma effluent and the plasma treatments show a strong correlation between the gas-phase concentration of N2O5 and inactivation of the virus. We experimentally show that the production of N2O5 coincides with the enhanced generation of reactive nitrogen species in the liquid phase.