Physicochemical properties and antimicrobial efficacy of argon cold atmospheric pressure plasma jet activated liquids – a comparative study

Cold atmospheric pressure plasma jet activated liquids (CAPJALs) have attracted considerable scientific attention due to their peculiar antimicrobial characteristics. In the current context, there is a need to compare the bactericidal activity of CAPJALs and demonstrate the specific parameters necessary to obtain greater effectiveness. This in-vitro research examines the antimicrobial activity of liquids, such as deionized water (DI-W), drinking water (DW), tap water (TW), and normal saline (NS) activated by Ar cold atmospheric pressure plasma jet (CAPJ) against multidrug-resistant (MDR) E. coli and S. aureus. The computed D- value showed that CAPJALs' bacterial inactivation efficacy followed the trend – DI-W ≈ NS > DW > TW for both the isolates. To obtain greater bactericidal effectiveness, an optimum combination of liquid activation time by CAPJ and CAPJAL – bacteria interaction time was noticed. In addition, the rate at which the physicochemical parameters (pH, electrical conductivity (EC), total dissolved solids (TDS), and concentration of reactive species (H₂O₂, NO₃^-, and NO₂^-)) changed within the liquid varied in different ways. It was observed that the identified gas-phase species (Ar I, Ar⁺, N₂, N₂⁺, O I, OH•, OH⁺, NO⁺, O₂⁺, N₂O₃^-, NO₃^-, N₂O₂^-, etc.) would contribute to modification of liquid physicochemical property by generating liquid phase reactive species (NO₃^-, NO₂^-, H⁺, H₂O₂, ONOOH, Cl₂, HOCl, etc.) via reaction cascades. These reactive species in the liquid phase, together with other physicochemical characteristics, were found to play a part in the process of bacterial inactivation. This study into the underlying mechanism of CAPJ – liquid and CAPJAL – bacteria interaction would help to determine its potential use as a disinfectant in healthcare settings.

List of microorganisms

E. coli: Escherichia coli; S. aureus: Staphylococcus aureus.