Characterization and bacterial inactivation application of multiple pin-to-plate electrode-based DBD plasma driven by nanosecond-pulsed high voltage

A diffuse and large-area dielectric barrier discharge (DBD) filled with air and helium gas mixtures was generated by a unipolar nanosecond-pulsed high voltage. A large-gap multiple pin-to-plate electrode was employed to facilitate the insertion of well plates into the plasma discharge. The nanosecond high-voltage-pulsed discharge has unique advantages in producing a diffuse DBD plasma. We examined the changes in the plasma properties upon varying operating parameters such as the gas composition and flow rate, as well as the pulse voltage. Various types of liquid (de-ionized, tap, and saline water, as well as phosphate buffered saline and LB broth) were exposed to the DBD plasma. The physicochemical properties (pH and electrical conductivity) and concentrations of reactive species generated in the treated liquids (such as H2O2, NO2-, and O-3, which play central roles in the aqueous-phase chemistry of plasma-treated liquids for bacterial inactivation) were measured as a function of the operating parameters. The nanosecond-pulsed DBD was observed to generate significantly higher level of reactive species in various types of liquid. For investigating the plasma treatment of liquids containing suspended microorganisms, 1 ml of Escherichia coli (E. coli) stock suspension was pipetted into 9 ml of DW. The resulting bacterial suspensions were treated with the DBD plasma for a selected time. Six-log E. coli reduction was achieved after 19 h of incubation. A DBD plasma generated in a gas mixture of ambient air and 2 slm helium exhibited an enhanced inactivation efficacy, which was correlated with the RONS concentration and pH in the plasma-treated liquids.