Quantification of the ozone and singlet delta oxygen produced in gas and liquid phases by a non-thermal atmospheric plasma with relevance for medical treatment

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.

On a heavy path – determining cold plasma-derived short-lived species chemistry using isotopic labelling

“…71 Especially the nal oxidation step from sulnic to sulfonic acid requires a gas phase-derived oxygen species, with O( 3 P) and O 2 ( 1 D g ) as potential candidates as shown from gas phase measurements and 0D/2D model simulation (reactions (5)-(9)). 27,[72][73][74][75]…”

“…Depending on plasma source, feed gas composition, and distance to the target, ROS/ RNS generation varies. [26][27][28][29][30] A major role of these plasmaderived ROS/RNS is assumed, 31,32 but incongruity regarding the mode of action exists. It was argued that cell membraneassociated proteins pick up and translate the induced signals 33 or that species can cross the cell membrane using specic pore proteins 34 and trigger intracellular responses via cytosolic sensor proteins 35 or the mitochondria.…”

“…+ 2H + + 2e À # 2H 2 O). 55,56 The presence of other species, such as hydroxyl radicals, superoxide anion radicals, or nitric oxide can be shown in liquids by electron paramagnetic resonance, 57 assumed from gas phase distributions, 27,58,59 or from the detection of modied organic or inorganic targets by the plasma treatment. 51,60 Given their high reactivity, the contribution of short lived ROS and RNS to the modication of biomolecules is assumingly signicant.…”

Non-touching plasma–liquid interaction – where is aqueous nitric oxide generated?

“…1,5 In a prior study, among others, the effect of the curtain gas on the oxygen species production was investigated. 77 There, also the suppression of the O concentration in the liquid in the presence of synthetic air surroundings was determined. In that study, increasing amounts of O 2 up to 1%, but no N 2 , were added to the feed gas.…”

“…Due to the gaseous formation processes, it could be stated that for direct treatment, as was the case in the here-presented study as well, the N 2 curtain gas mainly leads to the formation of aqueous O, whereas an extended treatment distance or a synthetic air curtain gas composition was dominated by the formation of O 3 . 77 This leads to the conclusion that O is an important precursor for aqueous NO, and in the presence of O 2 , O 3 is formed, which prevents the formation of aqueous NO. Therefore, using synthetic air as the curtain gas, it was expected that less or no NO-adducts are detectable in the plasma treated phosphate buffer.…”