Bacterial Inactivation in Liquids Using Multi-Gas Plasmas

Abstract

Using a multi-gas plasma jet, we generated plasmas of various gas species such as argon, oxygen, nitrogen, carbon dioxide, and air. Photometric measurements of colorforming reactions were used to identify singlet oxygen, OH radicals, hydrogen peroxide, NO radicals, nitrite, and nitrate, which are important sterilization agents that are generated in the liquid phase. Oxygen plasma generated the largest amount of singlet oxygen, OH radicals, and hydrogen peroxide. Air plasma generated NO radicals, nitrite, and nitrate. The pH of air plasma-treated water for 120 s dropped below 3.0. The air plasma sterilized Escherichia coli in distilled water after 120 s of treatment. In addition, when the initial pH was fixed below 3.6, E. coli was more effectively sterilized by oxygen plasma. Furthermore, dimethylsulfoxide, which is an OH radical scavenger, suppressed the sterilization effect of oxygen plasma.