Characteristics of DC gas-liquid phase atmospheric-pressure plasma and bacteria inactivation mechanism

A direct current (DC) gas-liquid phase atmospheric-pressure argon (Ar) plasma is used to inactivate Staphylococcus aureus suspended in the liquid. The characteristics of the gas-liquid plasma such as gas temperature, electron excitation temperature, and electron density are investigated by optical emission spectroscopy (OES). Direct plasma treatment for 40 min results in more than 2.0-log cell reduction. The emission spectra obtained from the gas-liquid phase plasma show the presence of hydroxyl radicals and atomic oxygen which give rise to effective inactivation of microorganisms. The energetic particles generated from the plasma tend to induce chemical effects such as formation of hydroxyl and hydrogen peroxide and reduced pH. The water sample after plasma treatment retains the inactivation ability for a long time and the germicidal effects arise from residual H₂O₂ and acidic pH. These effects have potential applications in plasma biomedicine and water purification. Atmospheric pressure cold plasmas have been thought to be a promising candidate for biomedical applications. In some cases, the plasmas contact living tissues where a gas-liquid environment forms between the body fluid and plasmas. The physical characteristics of plasmas or inactivation of bacteria in solutions are important. A gas-liquid phase Ar plasma is generated in a quartz glass tube immersed in water. Characteristics of the plasma, active species formation, and bacterial effects are investigated systematically. Understanding the characteristics and inactivation mechanism, we can use this technology for biomedical application or water purification effectively.