Influence of Controlling Plasma Gas Species and Temperature on Reactive Species and Bactericidal Effect of the Plasma

Yuma Suenaga,Akitoshi Okino,Yuriko Matsumura,Toshiki Aizawa,Atsuo Iwasawa,Toshihiro Takamatsu,Shohei Moriya

doi:10.3390/app112411674

Yuma Suenaga, Akitoshi Okino + Show 5 more

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https://doi.org/10.3390/app112411674

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Abstract

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.

Highlights

In the conventional plasma applications, high-temperature atmospheric plasma and low-pressure (1/10,000 atm) nonthermal plasma have been used for analysis [1] and semiconductor manufacturing [2]
In the nitrogen plasma generated in the atmosphere, spectroscopic measprevious study, we reported that more OH radicals were produced from nitrogen plasmas urements have indicated the existence of nitrogen atoms [13]
This study suggested the contribution of singlet oxygen to the bactericidal effect, which is consistent with the results of the present study

Summary

Introduction

In the conventional plasma applications, high-temperature (several thousand degreesCelsius or higher) atmospheric plasma and low-pressure (1/10,000 atm) nonthermal plasma have been used for analysis [1] and semiconductor manufacturing [2]. The stable generation of low-temperature plasma at approximately 50–100 ◦ C under atmospheric pressure has become possible. This has significantly expanded the range of plasma applications. Applications of plasma, such as in disinfection [3] and hemostasis [4], wound healing [5], analysis of surface-adhesive compounds [6], and mobile on-site analytical devices [7], are examples that take advantage of the characteristics of atmospheric pressure and lowtemperature generation of plasma. In atmospheric low-temperature plasmas, the gas temperature of the plasma is inevitably higher than room temperature (15–25 ◦ C), because energy is supplied to the gas at room temperature through discharge to generate the plasma [9]. For the treatment of plants and other heat-sensitive processing targets, it is necessary to design a system that allows processing to be performed at a temperature that

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