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.

Plasma-activated water (PAW) is receiving much attention in biomedical applications because of its reported potent bactericidal properties. Reactive oxygen and nitrogen species (RONS) that are generated in water upon plasma exposure are thought to be the key components in PAW that destroy bacterial and cancer cells. In addition to developing applications for PAW, it is also necessary to better understand the RONS chemistry in PAW in order to tailor PAW to achieve a specific biological response. With this in mind, we previously developed a UV–vis spectroscopy method using an automated curve fitting routine to quantify the changes in H ₂ O ₂ , NO ₂ ⁻ , NO ₃ ⁻ (the major long-lived RONS in PAW), and O ₂ concentrations. A major advantage of UV–vis is that it can take multiple measurements during plasma activation. We used the UV–vis procedure to accurately quantify the changes in the concentrations of these RONS and O ₂ in PAW. However, we have not yet provided an in-depth commentary of how we perform the curve fitting procedure or its implications. Therefore, in this study, we provide greater detail of how we use the curve fitting routine to derive the RONS and O ₂ concentrations in PAW. PAW was generated by treatment with a helium plasma jet. In addition, we employ UV–vis to study how the plasma jet exposure time and treatment distance affect the RONS chemistry and amount of O ₂ dissolved in PAW. We show that the plasma jet exposure time principally affects the total RONS concentration, but not the relative ratios of RONS, whereas the treatment distance affects both the total RONS concentration and the relative RONS concentrations.

Cold atmospheric plasmas have attracted significant worldwide attention for their potential beneficial effects in cancer therapy. In order to further improve the effectiveness of plasma in cancer therapy, it is important to understand the generation and transport of plasma reactive species into tissue fluids, tissues and cells, and moreover the rates and depths of delivery, particularly across physical barriers such as skin. In this study, helium (He) plasma jet treatment of a 3D cancer tumour, grown on the back of a live mouse, induced apoptosis within the tumour to a depth of 2.8 mm. The He plasma jet was shown to deliver reactive oxygen species through the unbroken skin barrier before penetrating through the entire depth of the tumour. The depth and rate of transport of He plasma jet generated H ₂ O ₂ , NO ₃ ⁻ and NO ₂ ⁻ , as well as aqueous oxygen [O ₂ (aq)], was then tracked in an agarose tissue model. This provided an approximation of the H ₂ O ₂ , NO ₃ ⁻ , NO ₂ ⁻ and O ₂ (aq) concentrations that might have been generated during the He plasma jet treatment of the 3D tumour. It is proposed that the He plasma jet can induce apoptosis within a tumour by the ‘deep’ delivery of H ₂ O ₂ , NO ₃ ⁻ and NO ₂ ⁻ coupled with O ₂ (aq); the latter raising oxygen tension in hypoxic tissue.

The plasma jet generation of reactive oxygen and nitrogen species (RONS) in solution is important in biology, medicine, and disinfection. Studies using a wide variety of plasma jet devices have been carried out for this purpose, making it difficult to compare the performance between devices. In this study, we compared the efficiency of RONS generation in deionized (DI) water between 3.7-mm- and 800-µm-sized helium (He) plasma jets (hereafter mm-jet and µm-jet, respectively) at different treatment distances and times. The efficiency of RONS generation was determined by considering the total amount of RONS generated in DI water with respect to the input energy and gas consumption. We found that the mm-jet generated 20% more RONS in the DI water than the µm-jet at the optimized distance. However, when the input power and He gas consumption were taken into account, we discovered that the µm-jet was 5 times more efficient in generating RONS in the DI water. Under the parameters investigated in this study, the concentration of RONS continued to increase as a function of treatment time (up to 30 min). However treatment distance had a marked effect on the efficiency of RONS generation: treatment distances of 25 and 30 mm were optimal for the mm-jet and µm-jet, respectively. Our method of comparing the efficiency of RONS generation in solution between plasma jets could be used as a reference protocol for the development of efficient plasma jet sources for use in medicine, biology, and agriculture.

We investigate the use of a DC-pulse-driven non-thermal atmospheric-pressure He plasma jet in the regulation of hydrogen peroxide (H₂O₂), nitrite (NO₂⁻), nitrate (NO₃⁻), and oxygen (O₂) in deionized (DI) water. The production of these molecules is measured by in situ UV absorption spectroscopy of the plasma-activated water (PAW). Variations in the pulse polarity and pulse width have a significant influence on the resultant PAW chemistry. However, the trends in the concentrations of H₂O₂, NO₂⁻, NO₃⁻, and O₂ are variable, pointing to the possibility that changes in the pulse polarity and pulse width might influence other plasma variables that also impact on the PAW chemistry. Overall, the results presented in this study highlight the possibility of using DC-pulse-driven plasma jets to tailor the chemistry of PAW, which opens new opportunities for the future development of optimal PAW formulations across diverse applications ranging from agriculture to medicine.