Temperature stability and effectiveness of plasma-activated liquids over an 18 months period

Non-buffered plasma-activated liquids such as water and saline have shown bactericidal effects. In the present study, we investigated the anti-bacterial efficacy and stability of plasma-activated water (PAW) and plasma-activated saline (PAS), generated using a high voltage dielectric barrier discharge system. This study compares the potential of non-buffered plasma-activated liquids (PAL) for the inactivation of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) after storage of the solutions at five different temperatures for a storage time up to 18 months after their generation. The temperatures used were room temperature, 4^◦ C, −16^◦ C, −80^◦ C, −150^◦ C. Both PAW and PAS achieved 6 log reduction for both bacteria on the first day of their generation after 60 min contact time and they retained these effects after 18 months when stored at the lowest temperatures. Chemical analysis of PAL showed that plasma caused a drop in pH, generation of reactive oxygen species and nitrates, whereas no nitrites are detected in the system used. The concentrations of chemical species were affected by the storage at different temperatures and a thermocouple probe was used to investigate the freezing behaviour of the PAL.