The impact of the carrier gas composition of non-thermal atmospheric pressure plasma jet for bacteria sterilization

In this work, the bacteria inactivation using the nonthermal atmospheric pressure plasma has been studied. The bacteria inactivation was conducted using a self-design nonthermal atmospheric pressure plasma jet system. During this experiment, Escherichia coli was used as an objective microorganism. The primary operating gas for the plasma jet used in this work is helium, and small fractions of oxygen or nitrogen (0.2%) were used as the secondary gas. The three plasma jet cases were operated at 3.5 kV, 14 l/m, and 7 mm, which represented the applied voltage, gas flow rate, and distance from the nozzle, respectively. The types of reactive species have been examined using optical emission spectroscopy. The gas temperature and optical emission spectrum were measured under the same condition. The active species of OH, OII, OI, N21+, N22+, and He are indented in the UV-vis wavelength range. The inactivation of E. coli bacteria has occurred after 20 s of nonthermal plasma treatment, whether the carrier gas is pure helium or helium + nitrogen or helium + oxygen. The results revealed that the impact of helium is less than that of helium + 0.2% nitrogen which is less than that of helium + 0.2% oxygen. The current results of this experiment could be utilized in improving the nonthermal plasma jet for extended surface decontamination.