Effect of gas composition on surface sterilization by using LF-microwave hybrid plasma source

A new type of atmospheric-pressure non-thermal plasma source was developed by a combining a low-frequency (LF) plasma jet with microwave plasma as a hybrid plasma. The LF-microwave hybrid plasma has a large amount of reactive species compared to conventional LF plasma jet owing to higher-energy electrons, which are accelerated by the oscillating electric fields of the microwave. Moreover, it can be sustained stably at a higher composition rate of the process gas in the discharge gas. The objective of this study is to investigate the effect of the admixture gas composition on surface sterilization by using our self-designed LF-microwave hybrid plasma source. The influence of the discharge gas composition ratio between oxygen and argon on the production of the reactive species and sterilization effect was investigated. The analysis of the optical emission spectra and the reaction of the chemical indicators reveal that reactive oxygen increases with the increasing ratio of oxygen in the oxygen-argon admixture discharge gas up to an oxygen ratio of 10% and then it saturates. In contrast, the results of the sterilization test using biological indicators indicate that a higher sterilization effect was obtained for a lower ratio of oxygen in the admixture discharge gas. It is considered that reactive species, except reactive oxygen, are related to surface sterilization using atmospheric-pressure non-thermal plasma.