Sterilization mechanism and material compatibility of low-pressure RF water plasma for spacecraft surface decontamination
摘要
Low-pressure radio-frequency water plasma is a promising sterilization method for spacecraft because it can achieve effective microbial inactivation at low temperature while potentially reducing damage to heat-sensitive materials. In this study, the applicability of low-pressure water plasma to spacecraft surface sterilization was comprehensively evaluated in terms of reactive-species generation, sterilization performance, sterilization mechanism, and material compatibility. Optical emission spectroscopy and a disodium terephthalate chemical probe confirmed that OH radicals were the major reactive species generated in the water plasma. Sterilization performance was assessed using Geobacillus stearothermophilus spores and the radiation-resistant bacterium Deinococcus radiodurans. The biological indicator reached a sterility assurance level (SAL) of 10⁻6 or lower within 60 min under water plasma treatment, whereas 90 min was required for oxygen plasma treatment. In cover-glass experiments, Geobacillus stearothermophilus reached the detection limit after 2 h of water plasma irradiation, whereas Deinococcus radiodurans required 4 h. Fourier-transform infrared spectroscopy of model organic compounds showed that water plasma degraded wool keratin more effectively than oxygen plasma, whereas oxygen plasma more strongly degraded dipicolinic acid. These results suggest that water plasma promotes microbial inactivation primarily through preferential oxidative degradation of proteinaceous protective surface structures. In addition, water plasma caused less chemical-bond degradation in polyimide film than oxygen plasma, indicating superior material compatibility. Overall, low-pressure water plasma combines high sterilization efficacy with low material damage and is therefore a promising candidate for spacecraft surface sterilization.