Reactive species generation and biocidal efficiency of an asymmetric DBD APPJ
Résumé
Summary form only given. Atmospheric Pressure Plasma Jets (APPJ) are now well established in the community as a versatile source of reactive species at relatively low temperature. The applications range from nanomaterial synthesis and analytical chemistry to soft decontamination of sensible surfaces. For each application, the reactive species created must be identified and quantified, in the gas phase, as well as in the liquid phase. The aim of this study was to investigate the correlation between the plasma-induced inactivation of bacteria in the liquids and production of reactive species inside the bacterial suspensions.The asymmetric DBD APPJ used in this study has been described with great detail in previous work1. It consists of a 38 mm diameter cylindrical grounded electrode (15 mm length) and a 7 mm to 3 mm conical live electrode (36 mm length). The distance between the two electrodes is fixed to 10 mm. The live electrode is powered with a square wave AC voltage at 20 kHz and 2.5 kV. The gas injected in the plasma jet is Helium, with 0 to 0.5% O2, at 2.1 L min-1. E. coli (ATCC 25992) was grown overnight in tryptic soy broth and then washed and resuspended in phosphate buffer or saline. After plasma exposure the bacterial suspension was recovered and the number of surviving bacteria was estimated by CFU counting after incubation of tryptic soy agar for one day. Treated bacterial suspension was also used to assess two other viability parameters - the cell respiration (XTT assay) and cell permeability using fluorescent dyes (LIVE/DEAD BacLight Viability Kit). The gas phase reactive species (e.g. N2, OH, O) were assed using spatially resolved optical emission spectroscopy (Ocean Optics) and filtered ICCD camera imaging (Princeton Instruments). Colorimetric assays were used to determine the concentrations of ozone, hydrogen peroxide and nitrite in the liquid phase. The understanding of the relation between the reactive species production and the biocidal capacitie...