In this study, plasma gas species and temperature were varied to evaluate the reactive species produced and the bactericidal effect of plasma. Nitrogen, carbon dioxide, oxygen, and argon were used as the gas species, and the gas temperature of each plasma was varied from 30 to 90 °C. Singlet oxygen, OH radicals, hydrogen peroxide, and ozone generated by the plasma were trapped in a liquid, and then measured. Nitrogen plasma produced up to 172 µM of the OH radical, which was higher than that of the other plasmas. In carbon dioxide plasma, the concentration of singlet oxygen increased from 77 to 812 µM, as the plasma gas temperature increased from 30 to 90 °C. The bactericidal effect of carbon dioxide and nitrogen plasma was evaluated using bactericidal ability, which indicated the log reduction per minute. In carbon dioxide plasma, the bactericidal ability increased from 5.6 to 38.8, as the temperature of the plasma gas increased from 30 to 90 °C. Conversely, nitrogen plasma did not exhibit a high bactericidal effect. These results demonstrate that the plasma gas type and temperature have a significant influence on the reactive species produced and the bactericidal effect of plasma.

The aim of the study was to design and build a multi-gas temperature-controllable plasma jet that can control the gas temperature of plasmas with various gas species, and evaluated its temperature control performance. In this device, a fluid at an arbitrary controlled temperature is circulated through the plasma jet body. The gas exchanges heat with the plasma jet body to control the plasma temperature. Based on this concept, a complex-shaped plasma jet with two channels in the plasma jet body, a temperature control fluid (TCF) channel, and a gas channel was designed. The temperature control performance of nitrogen gas was evaluated using computational fluid dynamics analysis, which found that the gas temperature changed proportionally to the TCF temperature. The designed plasma jet body was fabricated using metal 3D-printer technology. Using the fabricated plasma jet body, stable plasmas of argon, oxygen, carbon dioxide, and nitrogen were generated. By varying the plasma jet body temperature from −30 °C to 90 °C, the gas temperature was successfully controlled linearly in the range of 29–85 °C for all plasma gas species. This is expected to further expand the range of applications of atmospheric low temperature plasma and to improve the plasma treatment effect.

Ethanol has variable effectiveness against non-enveloped viruses; however, several reports suggest that it possesses virucidal activity against human adenoviruses (HAdVs). Ethanol concentrations between 45 w/w% and 95 w/w% showed sufficient activity against HAdV type 5 over a 30 s period, while concentration between 72.5 w/w% and 77 w/w% was effective against type 7 over 60 s period. Type 2 and 8 were less susceptible, however. In this study, we investigated the ability of different concentrations of ethanol to inactivate and change the structure of 19 HAdV types across six subgroups, using the virus infectivity titer for evaluation. After 1 min of ethanol treatment, HAdV types 5 and 8 were observed with transmission electron microscopy. The virucidal activity of disinfectant ethanol against HAdVs in subgroups A, B1 (except for type 21), and C was higher than that in subgroups B2, D, E, and F. We observed a ‘U-shaped’ fluctuation pattern where the reduction factor dropped at concentrations of 70–80% and then rose again at 90%. After treatment with 40% ethanol, TEM images showed no major changes in type 8 HAdVs, but organic matter was observed around the virus particles in type 5 HAdVs; after treatment with 66% ethanol, virus particles aggregated in both types. This suggests that HAdVs with a lower number of repeats in the shaft region exhibited higher ethanol resistance.