Effects of VUV/UV radiation and oxygen radicals on low-temperature sterilization in surface-wave excited O 2 plasma

Abstract

Effects of VUV/UV radiation and oxygen radicals on low-temperature sterilization in surface-wave excited O 2 plasma were studied. To examine the effect of VUV/UV radiation on the inactivation of microorganisms, a small metal chamber covered with an optical filter at the top to block the radicals and allow the VUV/UV radiation was placed inside the plasma chamber. With a LiF and a glass filter, two different emission spectra above 120 nm (LiF filter) and above 300 nm (glass filter) were examined. The spores of Geobacillus stearothermophilus with a population of 2.5 × 10 6 were put below the optical filter in the small chamber, which was filled with the oxygen gas at appropriate pressure or pumped down to 10 − 3 Pa. The survival curve showed that the vacuum condition inside a small chamber with a LiF filter was more efficient than the same O 2 gas pressure as that outside plasma chamber. From the SEM analysis of the spores, there was no obvious change in shape after plasma treatment with filter at vacuum condition. According to the present results, it is concluded that the etching effect by the oxygen radical is more efficient in inactivation process than the sterilizing effect by the VUV emission in the oxygen plasma.