Characterisation and potential control of reactive species formation during cold atmospheric plasma medium activation

Abstract Cold atmospheric plasma (CAP) has been studied for years in the context of cancer therapy, where it is efficient at inducing cell death. Reactive oxygen and nitrogen species (RONS), via oxidative stress, are reported to be responsible for the treatment effect, but the biological mechanisms involved are not fully understood. Cold plasma is very effective at producing RONS, but with very complex chemical kinetics, so in this study we propose to measure the concentrations of some species formed in the gas and aqueous phases to help understand the chemical interactions that could lead to an increase in the cancer treatment efficiency of cold plasma. An anticancer effect after exposure to CAP has been demonstrated on a prostate tumour cell line with both direct and indirect treatment. To determine RONS concentrations in both the gas and liquid phases, an experimental reactor was developed to allow different methods of analysis to be conducted in similar conditions and potentially simultaneously. In the gas phase, ozone and nitrogen oxides were evaluated and the influence of some physical parameters on their concentrations demonstrated using design of experiments. Nitrates, hydrogen peroxide, hydroxyl radicals and singlet oxygen have been produced in pure water, but in culture medium a significant concentration has only been measured for hydrogen peroxide. The components of culture medium appeared to scavenge the most reactive species. Future investigations will look at other key species, the influence of physical parameters on production of RONS in the liquid phase and also adjustment of the medium composition to prevent scavenging.