Detection And Regulation Of Radical Production In Plasma Treated Liquids

The optimization of a plasma source regarding the species production is of high relevance for a tailored therapeutic application [1]. Especially for treatment of cancer versus healthy cells, a selective impact of the plasma is desired [2]. It can be achieved either by varying concentrations of an active species or, in some cases, by different reactive species. In order to regulate the species output, species densities generated in plasma treated liquids have to be determined. Furthermore, the impact of the plasma parameters on the yielded concentrations need to be known. Therefore, the influence of the plasma parameters on ROS and RNS levels in physiologic liquids were investigated for the argon plasma jet kINPen09, which is quite similar to the certified medical product, the kINPen® MED.

For instance, the impact of molecular gas admixtures to the feed gas, treatment distance, treatment time as well as liquid ingredients were analyzed for different reactive oxygen or reactive nitrogen species. As the more stable species such as nitrite, nitrate, and hydrogen peroxide were already investigated in several studies[3-5] the focus was set on the short-lived species: radicals such as hydroxyl radicals (•OH), superoxide anion radicals (O2•-), or nitric oxide (•NO). In addition, also highly reactive non-radicals such as singlet delta oxygen (1O2) or ozone (O3) were analyzed. These species are well known as relevant for biomedical application [6], furthermore, they are also known to be generated during plasma treatment of liquids in primary as well as in secondary and tertiary reactions [5].

By the use of different spin probes and spin traps, these radicals and non-radicals, generated during plasma treatment, were detected by electron paramagnetic resonance spectroscopy (EPR). The results obtained from the EPR, colorimetric and ion chromatographic measurements were compared with gas phase studies of a similar plasma source [7, 8] to determine their origin and potential adjustability.