Evaluation of cold atmospheric pressure plasma irradiation of water as a method of singlet oxygen generation

We used cold atmospheric pressure plasma jet to examine in detail (1)O(2) generation in water. ESR with 2,2,5,5-tetramethyl-3-pyrroline-3-carboxamide, a secondary amine probe, was used for the detection of (1)O(2). Nitroxide radical formation was detected after cold atmospheric pressure plasma jet irradiation of a 2,2,5,5-tetramethyl-3-pyrroline-3-carboxamide solution. An (1)O(2) scavenger/quencher inhibited the ESR signal intensity induced by cold atmospheric pressure plasma jet irradiation, but this inhibition was not 100%. As 2,2,5,5-tetramethyl-3-pyrroline-3-carboxamide reacts with oxidizing species other than (1)O(2), it was assumed that the signal intensity inhibited by NaN(3) corresponds to only the nitroxide radical generated by (1)O(2). The concentration of (1)O(2) produced by cold atmospheric pressure plasma jet irradiation for 60 s was estimated at 8 μM. When this (1)O(2) generation was compared to methods of (1)O(2) generation like rose bengal photoirradiation and 4-methyl-1,4-etheno-2,3-benzodioxin-1(4H)-propanoic acid (endoperoxide) thermal decomposition, (1)O(2) generation was found to be, in decreasing order, rose bengal photoirradiation ≥ cold atmospheric pressure plasma jet > endoperoxide thermal decomposition. Cold atmospheric pressure plasma jet is presumed to not specifically generate (1)O(2), but can be used to mimic states of oxidative stress involving multiple ROS.