Plasma-activated medium (PAM) has a broad prospect in the medical field. However, how to define the plasma dose of PAM and what is the dose–response relationship of PAM on cells are still open questions of plasma medicine. In this paper, the plasma dose of PAM based on equivalent total oxidation potential (ETOP) is introduced, and the S-logistic model is used to describe the relationship between PAM dose and the corresponding lethal effects of cells. Experiments of PAM on A875/HaCaT cell viabilities indicate that ETOP as a plasma dose is suitable for PAM. Evidence of dose discrepancies in 50% response intensity suggests that ETOP can be used to maximize the lethality difference between normal/cancer cells. Further validation by the published literature again indicates that ETOP may provide a well-defined strategy in evaluating the selectivity of PAM treatment on different cell types.

One of the main barriers stopping plasma activated water (PAW) in many practical applications is its high energy cost. On the other hand, a careful review of published literature finds that all the studies reported on the PAW only focus on the reactive species generated in liquid, and there is no measurement of the possible reactive species in the gas phase during the generation of PAW, which might contain high concentration reactive species especially for the cases when gas bubbling is used during the generation of PAW. In this paper, an electrodeless plasma device is reported, where distilled water, tap water, and saline water are used as working liquid while O 2 , N 2 , and air are flowing through the liquid. Not only the reactive species presented in the liquid phase, the reactive species contained in the gas phase were analyzed for the first time in the field of PAW nitrogen fixation. It was found that the total number of moles of reactive species in gas phase is actually several times higher than that in liquid phase. Only when considering the reactive nitrogen species (RNS) in the liquid phase, the lowest energy cost is about 18.97 MJ/mol when air is flowing though the tap water. On the other hand, when both the RNS in liquid phase and in gas phase are included, the lowest energy cost achieved is 5.53 MJ/mol when air is flowing through distilled water, which is only one-seventh of the lowest energy cost reported on PAW. This study helps us shed light on plasma nitrogen fixation by using PAW, which has been greatly underestimated due to the overlooking of gas phase products of PAW in the past.

Non-thermal atmospheric pressure plasma jets (NAPPJs) using ambient air as the inducer are of particular and desirable interest but with significant challenges. In this study, we report an air APPJ driven by ionization in the afterglow region, resembling noble gas APPJs. A pin-to-nozzle electrode is used for the air plasma jet with a nanosecond-pulsed DC high voltage as the power supply. Results show that the nozzle diameter plays an essential role in forming the air plasma jet. When the nozzle diameter is 3 mm, the air APPJ is driven by ionization in the afterglow region which is proved by the following three phenomena. First, with an exposure time of 0.1 s, an obvious shiny line (the narrow channel plasma) formed by electron accumulation is observed in the jet. The narrow channel becomes much brighter with a grounding pin approaching the nozzle vertically. In comparison, there is no such phenomenon with a 1-mm diameter nozzle. Second, the afterglow region discharge current of the ionization-driven processes is hundreds of mA distinguished from airflow-driven processes, the afterglow region current of which is typically zero. By using E-FISH to measure the electric field in the afterglow region, it can detect the electric field which has a maximum value of 10.5 kV/cm. Third, the intensity of the N2+ band is much stronger with a 3-mm diameter nozzle than with a 1-mm diameter nozzle, indicating that the local electric field plays an important role in the discharge. We expect this study can offer useful guidelines on the design and understanding of ionization-driven air plasma jets.

Electric phenomena and magnetic phenomena are inseparable. The magnetic field affects the ionization balance and spatial distribution of the plasma. A new type of plasma discharges has been found in nitrogen at sub atmospheric pressure condition without external magnetic field. Because of its regular helical propagation pattern, it was called as helical plasma plume. Although a great deal of research has been carried out on the key characteristics of the helical plasma plume, the formation mechanism of it is still unclear, which affects its application in materials and nanotechnology. By applying magnetic field to helical plasma with different chirality, the regulation behavior of the external magnetic field on helical plasma is studied. It is found that the external magnetic field will make the helical plasma shrink or stretch. With the increase of the magnetic field intensity from 0mT to 200mT, the left-handedness helical plasma plume stretches under the magnetic field of S-pole. Conversely, the left-handedness chiral helical plasma plume contracts when the magnetic poles change to N-pole. However, when the chirality of helical plasma plume is changed to right-handedness by adjusting voltage, opposite phenomenon comparing to the previous one is observed. Moreover, the applied magnetic field also affects the divergence of helical plasma. With the increase of S-pole external magnetic field, the helical plasma plume stretches until the external magnetic field reach to 80mT. When the magnetic field intensity is 80mT, the helical plasma disappears. The plasma in the quartz tube appears as a divergent form. Then increase the magnetic field intensity to 160mT, and the plasma appears in the form of a helix again. Finally, in the process of changing the intensity of the magnetic field, the clarity of the helical plasma plume will also change. The radial electric field of helical plasma is calculated by electromagnetic wave theory, and the mechanism of the influence of external magnetic field on the behavior of helical plasma is clarified. It is found that the magnetic field force component of Lorentz force is the reason that external magnetic field regulates the behavior of helical plasma. This study lays a theoretical foundation for understanding the motion behavior of helical plasma, which is conducive to the practical application in the field of materials and nanotechnology.