@article{stapelmann_myers_quesada_lenker_ranieri_2021, title={Following O and OH in He/O-2 and He/H2O gas mixtures-from the gas phase through the liquid phase to modifications on a biological sample}, volume={54}, ISSN={["1361-6463"]}, url={https://doi.org/10.1088/1361-6463/ac18ec}, DOI={10.1088/1361-6463/ac18ec}, abstractNote={Abstract
               Applied cold atmospheric plasma allows for the controlled delivery of reactive oxygen and nitrogen species tailored for specific applications. Through the manipulation of the plasma parameters, feed gases, and careful consideration of the environment surrounding the treatment target, selective chemistries that preferentially influence the target can be produced and delivered. To demonstrate this, the COST reference microscale atmospheric pressure plasma jet is used to study the generation and transport of O and 
                     
                     
                        
                           
                              
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                  OH from the gas phase through the liquid to the biological model target cysteine. Relative and absolute species densities of 
                     
                     
                        
                           
                              
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                  OH and O are measured in the gas phase through laser induced fluorescence (LIF) and two-photon absorption LIF respectively. The transport of these species is followed into the liquid phase by hydrogen peroxide quantification and visualized by a fluorescence assay. Modifications to the model biological sample cysteine exposed to 
                     
                     
                        
                           
                              
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                  OH and H2O2 dominated chemistry (He/H2O (0.25%)) and O dominated chemistry (He/O2 (0.6%)) is measured by FTIR spectroscopy. The origin of these species that modify cysteine is considered through the use of heavy water (H
                     
                     
                        
                           
                              
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                  O) and mass spectrometry. It is found that the reaction pathways differ significantly for He/O2 and He/H2O. Hydrogen peroxide is formed mainly in the liquid phase in the presence of a substrate for He/O2 whereas for He/H2O it forms in the gas phase. The liquid chemistry resulting from the He/O2 admixture mainly targets the sulfur moiety of cysteine for oxidation up to irreversible oxidation states, while He/H2O treatment leads preferentially to reversible oxidation products. The more O or OH/H2O2 dominated chemistry produced by the two gas admixtures studied offers the possibility to select species for target modification.}, number={43}, journal={JOURNAL OF PHYSICS D-APPLIED PHYSICS}, publisher={IOP Publishing}, author={Stapelmann, Katharina and Myers, Brayden and Quesada, Maria Herrera and Lenker, Eleanor and Ranieri, Pietro J.}, year={2021}, month={Oct} }
 @article{myers_ranieri_smirnova_hewitt_peterson_quesada_lenker_stapelmann_2021, title={Measuring plasma-generated center dot OH and O atoms in liquid using EPR spectroscopy and the non-selectivity of the HTA assay}, volume={54}, ISSN={["1361-6463"]}, url={https://doi.org/10.1088/1361-6463/abd9a6}, DOI={10.1088/1361-6463/abd9a6}, abstractNote={Abstract
               Plasma-generated hydroxyl radicals (·OH) and oxygen atoms (O) produced by the COST reference plasma jet, a micro-scaled atmospheric pressure plasma jet, were investigated using a variety of experimental techniques. Several gas admixtures were studied to distinguish the contributions of the two reactive oxygen species. Large discrepancies between inferred aqueous ·OH densities were noted when using a 2-hydroxyterephthalic acid (HTA) fluorescence assay and electron paramagnetic resonance (EPR) measurements with the spin trap 5,5-dimethyl-1-pyrroline N-oxide—especially when oxygen was present in the feed gas. A series of follow-up experiments including optical emission spectroscopy, H2O2 quantification, and EPR measurements of atomic oxygen using the spin trap 2,2,6,6-tetramethylpiperidine, revealed that the inconsistencies between the measured aqueous ·OH were likely due to the propensity of atomic oxygen to hydroxylate TA in a manner indistinguishable from ·OH. This renders the HTA assay non-selective when both ·OH radicals and atomic oxygen are present, which we report for all three gas admixtures in our experiments. Additionally, considerable degradation of both HTA and the spin adducts measured using EPR spectroscopy was apparent, meaning actual radical densities in the plasma-treated liquid may be considerably higher than implied. Degradation rates compared favorably to previously measured gas phase densities of atomic oxygen in the predecessor of the COST jet and reported degradation of other chemical probes. These results show the prolific role of atomic oxygen in plasma-induced liquid chemistry and caution against diagnostic techniques that are unable to account for it.}, number={14}, journal={JOURNAL OF PHYSICS D-APPLIED PHYSICS}, publisher={IOP Publishing}, author={Myers, B. and Ranieri, P. and Smirnova, T. and Hewitt, P. and Peterson, D. and Quesada, M. Herrera and Lenker, E. and Stapelmann, K.}, year={2021}, month={Apr} }