Sterilization using OH radicals produced by pulsed discharge plasma in atmospheric pressure

Nonthermal discharge plasma was used in sterilization. Using Ar as a carrier gas, H₂O₂ was nebulized and the gas was treated by pulsed discharge plasma generated under atmospheric pressure in a concentric cylindrical electrode energized with a sharp-rising square wave voltage (peak voltage 15-22 kV, frequency 230-240 Hz). The concentration of H₂O₂(35%) and H₂O(65%) in the carrier gas was about 1% in volume. Spectroscopic analyses or the Ar-plasma with H₂O₂ indicated a light emission caused by OH radicals. Bacillus subtilis spore was used as the sample. The spores were applied on a plastic film or 1 cm² area with the density of the spore about 10⁷/cm². The test samples were exposed to the plasma-excited gas. The sample spores were strongly inactivated, and the decimal reduction time of 30 sec was obtained. The degree of sterilization achieved in the experiment suggests the possibility of applying the nonthermal plasma process to dry-type sterilization under atmospheric pressure