Surface sterilization using LF-microwave hybrid plasma

Surface sterilization using LF-microwave hybrid plasma, which is a low-frequency (LF) plasma jet assisted by a microwave discharge, was investigated. Hybrid plasma is an atmospheric pressure non-thermal plasma and has a large number of reactive species. To improve the performance of surface sterilization using LF-microwave hybrid plasma, two types of discharge gas supply systems were employed. The first type (Type I) introduces argon and oxygen gas flows separately into the discharge region. The second type (Type II) introduces a mixture of two gases into the discharge region. The analysis of optical emission spectra and chemical indicators showed that more reactive oxygen species were produced by the Type II gas supply system compared to that by Type I. Moreover, a lower gas temperature was obtained with the Type II system compared to that with Type I. The results of the sterilization test show that a higher sterilization effect was obtained for the gas supply system Type II. The spore-forming bacteria (Geobacillus stearothermophilus) with a population of 2.4 × 106 CFU/carrier were sterilized for 50 s at the treatment temperature of 77.5 °C using the Type II gas supply system.