Reactive species in non-equilibrium atmospheric-pressure plasmas: Generation, transport, and biological effects

Abstract

Non-equilibrium atmospheric-pressure plasmas have recently become a topical area of research owing to their diverse applications in health care and medicine, environmental remediation and pollution control, materials processing, electrochemistry, nanotechnology and other fields. This review focuses on the reactive electrons and ionic, atomic, molecular, and radical species that are produced in these plasmas and then transported from the point of generation to the point of interaction with the material, medium, living cells or tissues being processed. The most important mechanisms of generation and transport of the key species in the plasmas of atmospheric-pressure plasma jets and other non-equilibrium atmosphericpressure plasmas are introduced and examined from the viewpoint of their applications in plasma hygiene and medicine and other relevant fields. Sophisticated high-precision, timeresolved plasma diagnostics approaches and techniques are presented and their applications to monitor the reactive species and plasma dynamics in the plasma jets and other discharges, both in the gas phase and during the plasma interaction with liquid media, are critically reviewed. The large amount of experimental data is supported by the theoretical models of reactive species generation and transport in the plasmas, surrounding gaseous environments, and plasma interaction with liquid media. These models are presented and their limitations are discussed. Special attention is paid to biological effects of the plasma-generated reactive oxygen and nitrogen (and some other) species in basic biological processes such as cell metabolism, proliferation, survival, etc. as well as plasma applications in bacterial inactivation, wound healing, cancer treatment and some others. Challenges and opportunities for theoretical and experimental research are discussed and the authors' vision for the emerging convergence trends across several disciplines and application domains are presented to stimulate critical discussions and collaborations in the future. 4 3.5 Optical absorption spectroscopy 3.5.1 Ozone 3.5.2 UV broadband absorption of OH density 3.5.3 Cavity ring-down spectroscopy 3.5 Selected non-optical techniques 3.5.1 Mass spectrometry 3.5.2 Flow visualization 3.5.3 Electron paramagnetic resonance spectroscopy 4. Temporal and spatial behaviour of key reactive species 4.1 Electron density (n e) 4.2 O atoms 4.2.1 Effect of admixture of O 2 /air on O concentration 4.2.2 Diffusion effect of shielding gas on O production 4.3 OH radical 4.3.1 Effect of H 2 O admixture on OH concentration 4.3.2 Effect of gas flow on OH concentration 4.3.3 Effect of O 2 on OH production 4.3.4 Effect of the treated samples on OH concentration 4.3.4.1 Effect of humidity of treatment sample on OH distribution 4.3.4.2 Effect of sample conductivity on OH distribution 4.3.4.3. Effect of the amplitude of the applied voltage on OH distribution 4.3.4.4. The effect of gas flow on OH distribution 4.3.4.5. The effect of the surface characteristics on OH distribution 4.3.5 Effe...

Power measurement for an atmospheric pressure plasma jet at different frequencies: distribution in the core plasma and the effluent

“…5) is that with the present device a higher power conversion into the "effluent" and accordingly into the production of reactive species for the plasma medical application [1,4] can be achieved by increasing the operation frequency. At this point, the individual challenges of this field of application has to be considered.…”

“…In plasma medicine, the aspect of efficacy is yet a topic for discussion, since the classification of effective agents is difficult due the variety, the individual response of the treated object, and the difficulties to measure them [1,4]. Especially in the case of plasma jets, the "effluent" that interacts with the surface is not identical with the "core" plasma in the ignition zone.…”

Jet‐to‐jet interactions in atmospheric‐pressure plasma jet arrays for surface processing

“…[39,40] The O 3 can cause damage to mucous and respiratory tissues in animals and also tissues in plants and NO is necessary for macrophages acting against microorganisms and tumors. [1,2] The uniformity of the distribution of those short-lived and longlived active species is important for the treatment effects of plasma surface applications.…”

“…Thus, APPJ has substantial advantages in treating living tissues and electric heat-sensitive materials. [1][2][3][4] The properties of the plasma plume blown outside of the discharge tube and into surrounding air can be easily controlled by changing the APPJ configuration, working gas, and the applied voltage. Therefore, APPJ is suitable for potential applications in materials processing, plasma biomedicine, surface decontamination, and thin film deposition.…”

Time Behaviour of Helium Atmospheric Pressure Plasma Jet Electrical and Optical Parameters

“…The geometrical parameters of these plasma jets and the materials used to assembly the device are very numerous [5]. Thus sometimes the biological effects of plasma jets are strongly conflicting, being even opposite in certain studies [6][7][8][9][10].…”