A microwave-excited atmospheric-pressure plasma jet (uAPPJ) exhibited a synergistic sterilization effect when combined with hydrogen peroxide (H 2 O 2 ), distilled water (DW) and titanium dioxide (TiO 2 ) photocatalysis. The sterilization efficacy of H 2 O 2 -uAPPJ increased as the H 2 O 2 concentration increased. The addition of TiO 2 also remarkably increased the sterilization efficacy. To find the main factor for the sterilization effect, optical emission spectra and the degradation rate of a methylene blue solution were measured. Numerical analysis, a newly developed global modeling, was also conducted to discover the mechanisms. Both experimental measurements and global modeling results suggested that combinations of H 2 O 2 , DW and TiO 2 increased the generation of hydroxyl radicals (•OH), which are known to be strong bactericidal agents. It was revealed that charged species, especially electrons, have a dominant role in the increase of •OH.

A new type of microwave-excited atmospheric pressure plasma source, based on the principle of parallel plate transmission line resonator, is developed for the treatment of large areas in biomedical applications such as skin treatment and wound healing. A stable plasma of 20 mm width is sustained by a small microwave power source operated at a frequency of 700 MHz and a gas flow rate of 0.9 slm. Plasma impedance and plasma density of this plasma source are estimated by fitting the calculated reflection coefficient to the measured one. The estimated plasma impedance shows a decreasing trend while estimated plasma density shows an increasing trend with the increase in the input power. Plasma uniformity is confirmed by temperature and optical emission distribution measurements. Plasma temperature is sustained at less than 40 °C and abundant amounts of reactive species, which are important agents for bacteria inactivation, are detected over the entire plasma region. Large area treatment ability of this newly developed device is verified through bacteria inactivation experiment using E. coli. Sterilization experiment shows a large bacterial killing mark of 25 mm for a plasma treatment time of 10 s.