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The application of cold atmospheric plasma jet in cancer treatment has received extensive attention. Research on the spatial distribution of the anticancer effects induced by plasma jet is of great significance for further promoting its clinical application. Here, based on two-dimensional monolayer cells and three-dimensional (3D) multicellular tumor spheroids, the distributions of anticancer effects induced by He plasma jet irradiation on tumor tissue were studied in detail. It was found that the effective anticancer area of the plasma jet was affected by the gas flow rate. Further studies showed that the plasma jet caused physical damage in the central region of the anticancer area and induced apoptosis in the peripheral region due to the reactive oxygen species (ROS) generated by the plasma jet. In addition, the anticancer results on 3D multicellular tumor spheroids indicated that the apoptosis rate and the anticancer depth of the plasma jet were different at different distances from the plasma-irradiated spot. This study could help us better understand the actual anticancer effects of a plasma jet on living tumor tissues, and it may provide beneficial information for optimizing the plasma jet treatment method in future clinical applications. [ABSTRACT FROM AUTHOR]

The transportation of drugs through model tissues that are being treated by an argon plasma jet was investigated in this paper. Gelatin gel films were used to construct the model tissues and lidocaine was used as a representative drug. The argon plasma jet enhanced the penetration of lidocaine and the enhancement rate increased with the discharge voltage and the frequency. When the discharge power of the plasma jet was low, it was deduced that the enhancement effect was mainly attributed to the electric field of the plasma jet. The enhancement effect was holistic and was hindered by the macromolecules of gelatin in the model tissues. When the discharge power of the plasma jet increased beyond a threshold level, the surface streamers of the plasma jet produced a deformation effect in the model tissue, thereby resulting in a star-shaped pattern on the surface of the model tissue. In that case, the penetration enhancement of lidocaine was dominated by the deformation effect; however, it was mainly confined to the surface layer. For comparison, a helium plasma jet was also used to enhance the penetration of lidocaine. When the discharge power was low, the enhancement effect of the helium plasma jet was higher than that of the argon plasma jet because the He gas flow and the electric field of He plasma jet enhanced the penetration of lidocaine jointly; however, the enhancement effect of the Ar plasma jet was only attributed to the electric field. When the discharge power increased beyond a threshold level, the enhancement effects of the two plasma jets were almost the same. [ABSTRACT FROM AUTHOR]

The transportation of reactive oxygen species (ROS) in model tissues treated by an Ar  +  O2 plasma jet was investigated in this paper. Gelatin gel was used to make the model tissues, and KI-starch reagent was used as an indicator of ROS including O3, O and HO2. It was found that the transportation of ROS covered almost the whole surface of the model tissue with good uniformity, despite the small size of the plasma jet source. The center part of the model tissue was almost undyed, of which the area increased slightly with the gas flow rate. The surface pattern of ROS moved downwards with the inclination angle of plasma irradiation, because the molecular weight of argon is larger than that of air. This downward trend could be stopped by adding a certain amount of helium into the Ar  +  O2 plasma jet, which is beneficial to precisely control the effective treatment area in clinical applications. Moreover, the dependence of the penetration depth of O3 on the plasma treatment time or the water content of model tissues was formulated, with a similar trend but lower penetration speed than that of the He  +  O2 plasma jet as reported previously. [ABSTRACT FROM AUTHOR]

In this paper, helium plasma jets are used for water activation to explore the production mechanism of H2O2 in the water. Either positive or negative DC voltage is used for the plasma excitation. It is found that the concentration of aqueous H2O2 induced by the positive plasma jet is ~4 times larger than that by the negative plasma jet with similar average discharge current. Three production pathways of aqueous H2O2 are considered important in literature, including the electrolysis, the dissolution of gaseous H2O2, and the combination of aqueous OH. However, the first two pathways are found to have similar contributions on H2O2 production for the positive and negative plasma jets. It is deduced that the OH combination in the surface layer of the plasma-activated water is most responsible for the concentration difference of aqueous H2O2 between the two plasma jets. [ABSTRACT FROM AUTHOR]

Argon is a widely used working gas of plasmas, which is much cheaper than helium but on the other hand much more difficult to generate diffuse discharge at atmospheric pressure. In order to meet the application requirements, plenty of researches have been reported to facilitate the diffuse discharge happening for argon plasmas, and in this paper an approach of using ethanol gas (EtOH) impurity is investigated. The discharge characteristics of Ar + EtOH plasma jet are studied as a function of the applied voltage and the concentration of EtOH, from which the concentration of EtOH between ∼200 and ∼3300 parts per million (ppm) is determined necessary for the generation of diffuse discharge. Compared with the helium plasma jet in literature, it is deduced that the diffuse discharge is probably caused by the Penning ionization happening between the metastable argon and EtOH. The discharge products of Ar + EtOH (672 ppm) plasma jet are measured and the corresponding chemistry pathways are analyzed. About 20% of EtOH is decomposed via complex chemical reactions to form more than a dozen of neutral species, such as CH3CHO, CH3COOH, CO, H2O, and CnH2n+2 (n ≥ 3), and various kinds of ionic species, including C+, CH+, ArH+, CH3CH2O−, etc. [ABSTRACT FROM AUTHOR]

In this paper, a novel large-scale plasma source is put forward, which can generate two modes of discharge, i.e. the surface dielectric barrier discharge and the plasma jet array, by just varying the helium gas flow rate. It is found that the discharge power changes a little with the increasing gas flow rate, but the densities of reactive species in the gas phase and in the treated water change a lot. In particular, the gaseous O3 has its density decreasing while the aqueous O3 has its concentration increasing with the increasing gas flow rate. In the plasma-treated water, the reactive nitrogen species such as nitrite and nitrate have their concentrations first increasing and then decreasing, while the reactive oxygen species such as H2O2, O3 and OH have their concentrations increasing monotonically, implying that the plasma source is well-adaptive for different application requirements. [ABSTRACT FROM AUTHOR]

A comparative study on aqueous reactive species in deionized water treated by two types of plasma jets is presented. Classified by the direction of the electric field in the jet device, a linear-field jet and cross-field jet have been set up. Concentrations of several aqueous reactive species are measured quantitatively by chemical fluorescent assays and electron spin resonance spectrometer. Results show that these two-type plasma jets would generate approximately the same gaseous reactive species under the same discharge power, but the linear-field plasma jet is much more efficient at delivering those species to the remote deionized water. This leads to a much more aqueous short-lived species including OH and produced in water, which are mainly correlated to the solvation of gaseous short-lived species such as ions and electrons. Regarding the long-lived species of aqueous H2O2, the concentration grows faster when treated by the linear-field plasma jet in the initial stage, but after 10 min it is similar to that treated by the cross-field counterpart due to the vapor–liquid equilibrium. The aqueous peroxynitrite is also predicted to be produced as a result of the air inclusion in the feeding gas. [ABSTRACT FROM AUTHOR]

In this paper, we report the observation of an interfacial pattern formation on the ITO surface by atmospheric pressure helium plasma jet-ITO interactions. By changing the voltage polarity of positive and negative pulses, the interfacial phenomenon displays two different pattern modes, i.e. a double ring pattern with a combination of homogeneous and filamentous modes as well as a single ring pattern with a homogeneous mode. The reasons may mainly be attributed to the spread of a radially outward traveling surface ionization wave that would cause electric field distributions and charge accumulations on the ITO surface. The spatial-temporal distribution of , He(3s3S), and O(3p5P) emissions are diagnosed to better understand the formation mechanism and the differences of plasma jet patterns under positive and negative polarities. Results show that the distribution of emission is the main contributor for generating the filament structure in a double ring pattern for positive polarity, the homogeneous mode pattern mainly depends on the distribution of O(3p5P) emission for positive and negative polarity. Additionally, in order to further systematically understand the behaviors of plasma jet patterns, some parametric results, such as behaviors versus pulse peak voltage, dielectric material, pulse repetition rate, and flow rate are investigated. Some interesting phenomena and additional insights for the plasma jet pattern are found with different parametric conditions. This study might help to better understand effects of plasma jets in interaction with surfaces, or its application in the medical sector. [ABSTRACT FROM AUTHOR]

In this paper, atmospheric pressure N2/O2 plasma jets with homogeneous shielding gas excited by nanosecond pulse are obtained to generate simplex reactive nitrogen species (RNS) and reactive oxygen species (ROS), respectively, for the purpose of studying the simplex RNS and ROS to induce the myeloma cell apoptosis with the same discharge power. The results reveal that the cell death rate by the N2 plasma jet with N2 shielding gas is about two times that of the O2 plasma jet with O2 shielding gas for the equivalent treatment time. By diagnosing the reactive species of ONOO−, H2O2, OH and in medium, our findings suggest the cell death rate after plasma jets treatment has a positive correlation with the concentration of ONOO−. Therefore, the ONOO− in medium is thought to play an important role in the process of inducing myeloma cell apoptosis. [ABSTRACT FROM AUTHOR]

Gelatin gels are used as surrogates of human tissues to study their barrier effects on incoming reactive oxygen and nitrogen species (RONS) generated by surface air discharge. The penetration depth of nitrite into gelatin gel is measured in real time during plasma treatment, and the permeabilities of nitrite, nitrate, O3 and H2O2 through gelatin gel films are quantified by measuring their concentrations in the water underneath such films after plasma treatment. It is found that the penetration speed of nitrite increases linearly with the mass fraction of water in the gelatin gels, and the permeabilities of nitrite and O3 are comparably smaller than that for H2O2 and nitrate due to differences in their chemistry in gelatin gels. These results provide a quantitative basis to estimate the penetration processes of RONS in human tissues, and they also confirm that the composition of RONS is strongly dependent on the tissue depth and the plasma treatment time. A small electric field of up to 20 V cm−1 can greatly reduce the barrier effects of the tissue model regardless of their directions, for which the underlying mechanism is unclear. However, the electric field force on the objective RONS should not be the dominant mechanism. [ABSTRACT FROM AUTHOR]