Abstract
In the field of plasma medicine, the identification of relevant reactive species in the liquid phase is highly important. To design the plasma generated species composition for a targeted therapeutic application, the point of origin of those species needs to be known. The dominant reactive oxygen species generated by the plasma used in this study are atomic oxygen, ozone, and singlet delta oxygen. The species density changes with the distance to the active plasma zone, and, hence, the oxidizing potential of this species cocktail can be tuned by altering the treatment distance. In both phases (gas and liquid), independent techniques have been used to determine the species concentration as a function of the distance. The surrounding gas composition and ambient conditions were controlled between pure nitrogen and air-like by using a curtain gas device. In the gas phase, in contrast to the ozone density, the singlet delta oxygen density showed to be more sensitive to the distance. Additionally, by changing the surrounding gas, admixing or not molecular oxygen, the dynamics of ozone and singlet delta oxygen behave differently. Through an analysis of the reactive species development for the varied experimental parameters, the importance of several reaction pathways for the proceeding reactions was evaluated and some were eventually excluded.
Highlights
Cold physical plasma jets have shown a high potential in the treatment of chronic wounds[1,2,3] and in cancer as an adjuvant to standard therapy[4]
Other species are harder to pinpoint, present in high amounts in the gas phase. This is valid for plasma generated ozone, O340, and singlet delta oxygen, O2(a1Δg)[41], whose full biological impact in plasma medicine is far from being completely known
During the plasma treatment of DPBS (Dulbecco’s phosphate buffered saline solution), several reactive oxygen species are induced in the liquid[10]: O3, O, or O2(a1Δg)
Summary
Cold physical plasma jets have shown a high potential in the treatment of chronic wounds[1,2,3] and in cancer as an adjuvant to standard therapy[4]. Besides electromagnetic radiation (ultraviolet - UV - up to near infrared - NIR - spectral range), atmospheric pressure plasma jets generate various reactive oxygen and reactive nitrogen species (RNS), such as ozone, singlet delta oxygen, hydroxyl radicals, superoxide anion radicals, nitric monoxide, nitrogen dioxide, nitrite, and nitrate[8] Most of these species are thought to interact directly or indirectly with biological systems, e.g. cells in a human body. The O2 content of the working gas was regulated This approach allows tuning the reactive species composition in the solution and increases the treatments reproducibility[17,59,60,61], forming the base for the presented data. The final aim of the present paper is to estimate the potential biological impact of these two ROS, O3 and O2(a1Δg), and to evaluate the suitability of direct and indirect treatment procedures
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