The efficacy of helium (He) and argon (Ar) plasma jets are being investigated for different healthcare applications including wound and cancer therapy, sterilisation and surface disinfections. Current research points to a potential link between the generation of reactive oxygen and nitrogen species (RONS) and outcomes in a range of biological and medical applications. As new data accrue, further strengthening this link, it becomes important to understand the controlled delivery of RONS into solutions, tissue fluids and tissues. This paper investigates the use of He and Ar plasma jets to deliver three RONS (hydrogen peroxide—H ₂ O ₂ , nitrite— NO 2 − and nitrate— NO 3 − ) and molecular oxygen (O ₂ ) directly into deionised (DI) water, or indirectly into DI water through an agarose target. The DI water is used in place of tissue fluid and the agarose target serves as a surrogate of tissue. Direct plasma jet treatments deliver more RONS and O ₂ than the through-agarose treatments for equivalent treatments times. The former only deliver RONS whilst the plasma jets are ignited; the latter continues to deliver RONS into the DI water long after the plasmas are extinguished. The He plasma jet is more effective at delivering H ₂ O ₂ and NO 2 − directly into DI water, but the Ar plasma jet is more effective at nitrating the DI water in both direct and through-agarose treatments. DI water directly treated with the plasma jets is deoxygenated, with the He plasma jet purging more O ₂ than the Ar plasma jet. This effect is known as ‘sparging’. In contrast, for through-agarose treatments both jets oxygenated the DI water. These results indicate that in the context of direct and indirect plasma jet treatments of real tissue fluids and tissue, the choice of process gas (He or Ar) could have a profound effect on the concentrations of RONS and O ₂ . Irrespective of operating gas, sparging of tissue fluid (in an open wound) for long prolonged periods during direct plasma jet treatment, could have implications for healthy tissue function; whilst through-tissue plasma jet treatment may provide a method to reperfuse oxygen-starved tissue. The assays described in this paper can be readily adopted (by others) and may support the future development of plasma sources to deliver specific (metered) doses of RONS.

DNA damage in the A549 human lung cancer cell line treated with cold plasma irradiation was investigated. We confirmed that cold atmospheric plasma generated reactive oxygen and nitrogen species (RONS) in a liquid, and the intracellular RONS level was increased in plasma-irradiated cells. However, a notable decrease in cell viability was not observed 24 hours after plasma irradiation. Because RONS induce oxidative damage in cells, strand breaks and chemical modification of DNA in the cancer cells were investigated. We found that 8-oxoguanine (8-oxoG) formation as well as DNA strand breaks, which have been thoroughly investigated, were induced by plasma irradiation. In addition, up-regulation of 8-oxoG repair enzyme was observed after plasma irradiation.

To investigate the potential role of the hydroxyl radical (^•OH) in cold atmospheric plasma (CAP) jet treatment, two fluorescence-based methodologies are utilised to measure DNA strand breaks. The first comprises a model system of a double-stranded DNA oligomer, where the respective strand ends are tagged with fluorophore and quencher molecules; and the second, a cell culture system reporting DNA strand breaks using the γ-H2AX assay. During the various CAP jet treatments, optical emission spectroscopy is used to detect the ^•OH in the gas phase and electron spin resonance is used to detect the ^•OH in solution. The CAP jet production of the ^•OH is shown to correlate to CAP jet induced DNA damage both with the DNA model and in biological cells. Results indicate that the CAP jet induces a higher degree of DNA damage when the CAP plume is in contact with the target solution. The potential of a ‘plasma screen’ based upon a hydrogel film, as a method to remove the DNA-damaging ^•OH species from reaching skin cells, is shown to significantly reduce DNA damage whilst facilitating the delivery of hydrogen peroxide. These findings could aid in the development of CAP jet-based applications where DNA damage is the objective (e.g. in cancer treatment) and others where it is to be avoided, e.g. in open-wound treatment and dermatology.

We employed UV–vis spectroscopy to monitor real-time changes in the oxygen tension and concentration of reactive oxygen and nitrogen species (RONS) in deionized (DI) water during treatments with helium (He) and argon (Ar) gas plasma jets. He and Ar gas jets are both shown to de-oxygenate DI water with He being more efficient than Ar, whilst the plasma jets deliver and regulate the concentrations of hydrogen peroxide (H ₂ O ₂ ), nitrite (NO ₂ ⁻ ) and nitrate (NO ₃ ⁻ ) in DI water. The H ₂ O ₂ and NO ₃ ⁻ production efficiency varied between He and Ar plasma jets, but was similar for NO ₂ ⁻ . Whilst DI water fully equilibrated with ambient air prior to treatment (de-oxygenated by both plasma jets) when DI water was first de-oxygenated by an inert gas jet treatment, both plasma jets were found to be capable of oxygenating DI water. These insights were then used to show how different combinations of plasma jet and inert gas jet treatments can be used to modulate O ₂ tension and RONS chemistry. Finally, potential further improvements to improve control in the use of plasma jets in regulating O ₂ and RONS are discussed.