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Electrically generated cold atmospheric plasma is being intensively researched for novel applications in biology and medicine. Significant attention is being given to reactive oxygen and nitrogen species (RONS), initially generated upon plasma-air interactions, and subsequently delivered to biological systems. Effects of plasma exposure are observed to millimeter depths within tissue. However, the exact nature of the initial plasma-tissue interactions remains unknown, including RONS speciation and delivery depth, or how plasma-derived RONS intervene in biological processes. Herein, we focus on current research using tissue and cell models to learn more about the plasma delivery of RONS into biological environments. We argue that this research is vital in underpinning the knowledge required to realize the full potential of plasma in biology and medicine. Physical effects of plasma can be seen to depths of several hundred micrometers within tissue.Plasma-derived RONS are likely to be delivered millimeters into tissues.Speciation reveals that RONS delivered by plasma into tissue fluid and tissue are predominately stable secondary RONS - for example, H 2 O 2 , NO 2 - , and NO 3 - .The plasma generation of RONS within a hydrated target is influenced by the target matrix that can enhance or reduce the RONS concentrations and act as a reservoir of RONS.It is likely that the concentration of these plasma-derived RONS exceeds hundreds of micromoles, even at depths of several millimeters within tissue.Oxygen concentration at the time of plasma treatment significantly influences RONS generation within a hydrated proteinaceous target. Refereed/Peer-reviewed

We explore how to configure an argon atmospheric-pressure plasma jet for enhancing its production of hydrogen peroxide (H2O2) in deionised water (DIW). The plasma jet consists of a quartz tube of 1.5 mm inner diameter and 3 mm outer diameter, with an upstream internal needle electrode (within the tube) and a downstream external cylindrical electrode (surrounding the tube). The plasma is operated by purging argon through the glass tube and applying a sinusoidal AC voltage to the internal needle electrode at 10 kV (peak–peak) with a frequency of 23.5 kHz. We study how the following operational parameters influence the production rate of H2O2 in water: tube length, inter-electrode separation distance, distance of the ground electrode from the tube orifice, distance between tube orifice and the DIW, argon flow rate and treatment time. By examining the electrical and optical properties of the plasma jet, we determine how the above operational parameters influence the major plasma processes that promote H2O2 generation through electron-induced dissociation reactions and UV photolysis within the plasma core and in the plasma afterglow; but with a caveat being that these processes are highly dependent on the water vapour content from the argon gas supply and ambient environment. We then demonstrate how the synergistic action between H2O2 and other plasma generated molecules at a plasma induced low pH in the DIW is highly effective at decontaminating common wound pathogens Gram-positive Staphylococus aureus and Gram-negative Pseudomonas aeruginosa. The information presented in this study is relevant in the design of medical plasma devices where production of plasma reactive species such as H2O2 at physiologically useful concentrations is needed to help realise the full clinical potential of the technology.

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. © 2018 The Japan Society of Applied Physics.

Thesis (PhD(Biomaterials Engineering and Nanomedicine))--University of South Australia, 2019. Includes bibliographical references. Renewed optimism that plasma can be developed as a medical tool has in the past two decades stimulated a surge in research into both the fundamentals and applications of plasma devices. A wide range of plasma devices and potential medical uses are currently being investigated, and relevant to this work are plasma jet designs and their uses in wound healing and management. Non-healing chronic wounds are a major healthcare challenge often resulting in limb amputation and death, and the direct cost of chronic wounds to Australia is $2.8bn p.a. In the context of wounds, it has been speculated that in both wound decontamination and wound healing the plasma jet delivery of reactive oxygen and nitrogen species (RONS) are likely to have a number of beneficial effects. This PhD project, employing a plasma jet device, focuses on understanding the measurement of RONS within the jet effluent and the fundamentals of plasma jet delivery of RONS into models of biological fluids, cells and tissue and the possible mechanisms involved in plasma-induced stimulation of wound healing. These are achieved by developing an arsenal of detection systems using molecular probes,electrochemical sensors, electron spin resonance or mass spectrometry to accurately and reliably quantify RONS delivered into in vitro models: into an artificial cell model (employing vesicles), tissue fluid, and tissue surrogates (using hydrogels).

With ambient mass spectrometry, we followed the transport of neutral gas species and ionic species through a 3.2 mm thick agarose tissue model target during He non-thermal atmospheric pressure plasma (NT-APP) jet treatment. We found that the neutral gas species are unable to efficiently penetrate the agarose target. But both positively and negatively charged ionic species readily penetrate through the agarose target, following an initial time-lag period of several minutes. Interestingly, we also found that the ionic species are easily hydrated. The trends in the He NT-APP jet transport of ionic species observed in this study correlate well with the He NT-APP jet transport of reactive oxygen and nitrogen species (RONS) through agarose tissue model targets that was investigated in previous studies. Therefore, mass spectrometry might prove to be a useful tool in the future for analyzing the dosages of NT-APP-generated RONS in real biological tissues. Refereed/Peer-reviewed

The helium (He) atmospheric-pressure plasma jet (APPJ) delivery of reactive oxygen and nitrogen species (RONS) and molecular oxygen (O2) in deionized (DI) water was monitored in real time using in situ UV absorption spectroscopy. The He APPJ was used to treat DI water directly and through an agarose target as a surrogate for tissue (e.g., a skin barrier). For direct treatment, the RONS were generated immediately in the DI water, and the concentration of RONS continued to increase during the He APPJ treatment. But there was only a very minor increase in the total RONS concentration detected after the plasma and gas flow were switched off. The agarose target delayed the generation of RONS into the DI water, but the total RONS concentration continued to increase long after (25 min) the plasma and gas flow were switched off. Direct treatment deoxygenated the DI water, whereas treatment through agarose resulted in oxygenation of the DI water. A dynamic change in the ratio of H2O2, NO2-, NO3-, and O2 was detected in the DI water during He APPJ treatment and 25 min after the He and gas flow were switched off for both direct and through-agarose treatment. These results have implications for the plasma treatment of real tissue where the dynamic changes in the RONS and O2 concentrations within the tissue and tissue fluid could affect cellular and physiological processes. Refereed/Peer-reviewed