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Plasma is highly efficient in the inactivation of microorganisms and is tried to be applied to the treatment of wounds. The gas activated by plasma, named plasma-activated gas, can also effectively inactivate microorganisms and get rid of the limitations of direct plasma treatment. However, the details of the interaction of plasma-activated gas on the tissue are still unclear. In this study, the agarose gel models in the presence of microorganisms to simulate the infected tissues were used to study the inactivation effects and mechanisms of plasma-activated gas. The inactivation depths in the gel models in the presence of microorganisms were related to the types of plasma-activated gas and the species of microorganisms. The Mixed-gas exhibited the strongest inactivation effects, and the inactivation depths in the gel models in the presence of bacteria were deeper than those in the presence of fungi. The long-lived species in the plasma-activated gas penetrated to more than 5.2 mm while the short-lived species only penetrated less than 2.3 mm, demonstrating the distinct roles of reactive species in the inactivation process. Moreover, the pig muscle was covered on the gel models to assess the penetration depths of the plasma-activated gas in muscle tissue and the focused plasma-activated gas could penetrate 1–1.5 mm of pig muscle. This study explored the inactivation effects and mechanisms on the gel models and the penetration depths in the real tissues of plasma-activated gas, which supplied the theoretical basis for the further application of plasma-activated gas in biomedical fields. [ABSTRACT FROM AUTHOR]

As an indirect application of cold atmospheric plasma, the use of plasma-activated solutions has recently attracted significant attention for intracavity tumor perfusion therapy. Here, an underwater plasma-bubble reactor with three discharge modes was applied to activate a cell culture medium, with the aim of inhibiting the growth of bladder cancer T24 cells in vitro. The results showed that although the reactive species in cell culture medium generated by the underwater bubble plasma varied between the dielectric barrier discharge (DBD) mode, spark mode, and hybrid mode, the plasma-activated cell culture medium (PAM) corresponding to all three discharge modes effectively decreased the viability of T24 cells. However, after co-culturing the PAM-pretreated T24 cells with normal T24 cells, it was observed that normal T24 cells were not affected by either the DBD or spark mode; however, the hybrid mode PAM-pretreated T24 cells further induced inactivation and apoptosis of normal T24 cells. Further studies suggested that the aqueous reactive species generated by the underwater bubble plasma in hybrid mode not only induced the apoptosis of T24 cells directly but also triggered PAM-pretreated T24 cell-derived exosome-mediated anticancer activity toward cancer cells. These results may provide a strategy for enhancing the anticancer extent and effect of PAM as well as advancing its clinical application. [ABSTRACT FROM AUTHOR]

The interaction between an atmospheric pressure plasma jet (APPJ) and an aqueous solution has great application prospects in biomedicine and many other fields. Reactive species adjacent to a water surface is critical to the activation of APPJ-treated water, which is affected by both the water evaporation and the admixture of ambient air. In this paper, taking He APPJ as an example, a two-dimensional (2D) cylindrically symmetric fluid model is developed to obtain the spatial distributions of gas components before discharging, and a series of global models are developed for the discharge in the boundary gas layer adjacent to the water surface. The interfacial distributions of reactive species and their fluxes onto the water surface are quantified. It is found that the electron density is 1016–1017 m−3 and it shows an annular distribution in the boundary gas layer. The density distributions of most reactive species there reveal ring-like shapes as well. The dominant cation and anion in such a boundary layer are H3O+ and OH−, respectively. The most abundant metastable is O2(a1Δ), the most abundant reactive oxygen species are H2O2 and OH, and the most abundant reactive nitrogen species are NO and HNO2. The species of H2O2, OH, HO2, and HNO2 are reportedly to have significant biological effects, and in our simulation, their fluxes onto the water surface are remarkable, higher than 1017 m−2 s−1. In addition, the effects of radial gas velocity and water evaporation on the particle flux distributions are also revealed. [ABSTRACT FROM AUTHOR]

Discharge characteristic comparisons between He and Ar plasma jets have been extensively reported, but is rarely reported for the comprehensive study of discharge mode transition from He jet to Ar jet, especially its induced liquid chemistry and biological effect. In this paper, we investigate the plasma jet mode transformation by varying the Ar contents in the He/Ar mixing working gas, particularly focusing on the effect of liquid chemistry of plasma activated water (PAW) and the corresponding inactivation effect against tumor cells in vitro. The mode transition process from He jet to Ar jet is characterized by the discharge images, the spatial temporal evolution, and the electrical and spectra measurements. It is found that the plasma jet mode displays a transition from diffuse to filamentous mode, which significantly affects the gaseous reactive species production and the ability to deliver into liquid, resulting in a huge difference in physicochemical properties and the concentration of reactive oxygen and nitrogen species in PAW. Furthermore, the A549 lung cancer cell is utilized to reveal the inactivation effect against tumor cells induced by PAW during discharge mode transition, and it is found that the PAW induced by Ar plasma jet can lead to the higher apoptosis efficiency of cancer cells due to the high production of key species (NO2−, H2O2, and ONOO−/ONOOH) under filamentous mode. This study would provide deep insights into the nature of liquid physicochemistry and its anticancer effect during plasma jet mode transformation. [ABSTRACT FROM AUTHOR]

Cold atmospheric plasmas have great application potential due to their production of diverse types of reactive species, so understanding the production mechanism and then improving the production efficiency of the key reactive species are very important. However, plasma chemistry typically comprises a complex network of chemical species and reactions, which greatly hinders identification of the main production/reduction reactions of the reactive species. Previous studies have identified the main reactions of some plasmas via human experience, but since plasma chemistry is sensitive to discharge conditions, which are much different for different plasmas, widespread application of the experience-dependent method is difficult. In this paper, a method based on graph theory, namely, vital nodes identification, is used for the simplification of plasma chemistry in two ways: (1) holistically identifying the main reactions for all the key reactive species and (2) extracting the main reactions relevant to one key reactive species of interest. This simplification is applied to He + air plasma as a representative, chemically complex plasma, which contains 59 species and 866 chemical reactions, as reported previously. Simplified global models are then developed with the key reactive species and main reactions, and the simulation results are compared with those of the full global model, in which all species and reactions are incorporated. It was found that this simplification reduces the number of reactions by a factor of 8–20 while providing simulation results of the simplified global models, i.e., densities of the key reactive species, which are within a factor of two of the full global model. This finding suggests that the vital nodes identification method can capture the main chemical profile from a chemically complex plasma while greatly reducing the computational load for simulation. [ABSTRACT FROM AUTHOR]

In this paper, the effect of the gas inlet orientation on the discharge characteristics of the coaxial dual-channel cross-field plasma jet is investigated. A working gas helium is separately flowed into the annular space between the hollow needle tube and the quartz tube (called Q-Jet), as well as the hollow needle tube (called N-Jet). With the same discharge parameters, the results show that the radial and axial dimensions of Q-Jet plasma jet are larger than that of N-Jet. Compared with the latter, the discharge current amplitude of the former increases by about 3.8-fold, the net charge transferred increases by about 8.8-fold, and the variety and density of reactive species produced are remarkably increased. For Q-Jet, the 706-nm spectral band is distributed inside and outside the quartz tube, while the 391-nm spectral band is mainly distributed outside the quartz tube, and the plasma jet forms a conical luminous pattern in the quartz tube during the positive half cycle of the voltage, due to the influence of helium viscosity. For N-Jet, 706- and 391-nm spectral bands are only just distributed in the axis of the quartz tube, and the charges left by the first discharge in the axial position of the quartz tube remarkably amplify the intensity of the second discharge in the positive half cycle. [ABSTRACT FROM AUTHOR]

Plasma-activated water (PAW) is considered to be an effective anticancer agent due to the diverse aqueous reactive oxygen and nitrogen species (RONS: ROS and RNS), but the drawback of low dose and short duration of RONS in acidified PAW limits their clinical application. Herein, this Letter presents an innovative therapeutic avenue for cancer treatment with highly-effective alkaline PAW prepared by air surface plasma. This anticancer alkaline formulation is comprised of a rich mixture of highly chemical RONS and exhibited a prolonged half-life compared to acidified PAW. The H2O2, NO2−, and ONOO−/O2− concentrations in the alkaline PAW can reach up to 18-, 16-, and 14-fold higher than that in acidic PAW, and the half-life of these species was extended over 8-, 10-, and 26-fold, respectively. The synergistic potent redox action between these RONS with alkaline pH was shown to be more potent than acidic PAW for cancer cell inhibition in vitro. Furthermore, the alkaline PAW injection treatment also significantly inhibited tumor growth in tumor-bearing mice. The possible reasons are that the alkaline PAW would disturb the acid extracellular milieu leading to the inhibition of tumor growth and progression; moreover, the efficient and durable RONS with alkaline pH could induce significant cell apoptosis by altering cell biomolecules and participating apoptosis-related signaling pathways. These findings offer promising applications for developing a strategy with real potential for tumor treatment in clinical applications. [ABSTRACT FROM AUTHOR]

Due to their good dielectric properties and low global warming potential, C4F7N–CO2 and C4F7N–N2 mixtures have shown promising potential to replace SF6 in high voltage gas insulated equipment. However, during manufacturing, installation, and transportation of power equipment, burs and metal particles can be inevitably left inside, and they can cause corona discharge. Fundamental investigation of the corona discharge mechanism is essential to monitor partial discharge signals in environmentally friendly power equipment. This paper applies the fluid model to investigate the discharge mechanism of C4F7N–CO2 and C4F7N–N2 mixtures in negative point-plane corona discharge. A 2D axisymmetric model combines the drift-diffusion equations for electrons, positive ions, and negative ions and Poisson's equation to study the process of dynamics. The gas is a mixture of C4F7N (5%, 7%, or 13%) and CO2 or N2 (95%, 93%, or 87%). The rise time of the first discharge pulse in C4F7N–CO2 and C4F7N–N2 mixtures is about 0.1 ns. The interval time between the first and the second pulse in the 5% C4F7N–95%CO2 mixture is about 1.5 times longer than that in the 5% C4F7N–95% N2 mixture. When the C4F7N content is 7% and 13%, the interval time between the first and second pulses in C4F7N–CO2 mixtures is about 2 and 3 times longer than those in C4F7N–N2 mixtures, respectively. The suppression regions in C4F7N–CO2 mixtures are larger than those in corresponding C4F7N–N2 mixtures. The total number of electrons, positive ions, and negative ions in C4F7N–CO2 mixtures is higher than that in C4F7N–N2 mixtures, while the reduced electric field in C4F7N–CO2 mixtures is smaller than that in C4F7N–N2 mixtures. [ABSTRACT FROM AUTHOR]

Cold atmospheric plasma in air commonly operates in the O3 mode and NOx mode, which easily interconvert through a transition mode, depending on discharge conditions. Given that the humidity varies considerably in different weather, it is important to elucidate the effect of humidity on the discharge mode transition, but few studies have been reported thus far. In this study, air plasmas were generated by a surface dielectric barrier discharge with different discharge powers of 6, 9, and 12 W, and the relative humidity of air was controlled at 1.5% (dry air), 40%, or 80% for a comparative study. It was found that an increase in humidity suppressed the production of O3 but promoted that of NO2 when the discharge power was 6 W, whereas it promoted the production of O3 but suppressed that of NO2 when the discharge power was 12 W. This implies that air humidity could have a bidirectional effect on the discharge mode transition, which was validated by experiments with a moderate power of 9 W. In that case, the discharge in dry air maintained the transition mode at a quasi-stable state, but it transited either into the NOx mode when the humidity was 40% or into the O3 mode when the humidity was 80%. A competition between reaction pathways dominated by N2(ν) or water-originated compounds may be the cause, and our findings indicate that the effect of humidity should be taken seriously in the research and development of air discharge plasmas. [ABSTRACT FROM AUTHOR]

In the field of plasma biomedicine, research on a plasma-activated medium (PAM) has attracted increasing attention in recent years because of its excellent characteristics. In this study, we used an atmospheric pressure air plasma jet to treat four different solutions: de-ionized water, RPMI 1640 medium, phosphate buffered saline (PBS), and saline. In order to investigate the property differences of different PAM, we mainly analyzed the physical and chemical properties and liquid-phase active species of different PAM and evaluated the inactivation of A549 lung cancer cells. The results show that the concentrations of long-lived reactive species (H2O2, NO2−, and NO3−) in different PAM increased with increasing treatment time. Biological experiments showed that the antitumor effects were in the order of PBS > saline > RPMI 1640 medium, and the best inactivation effect of plasma-activated PBS for 12 min was 89%. Meanwhile, plasma-activated PBS effectively promoted apoptosis in A549 cells, and the highest apoptosis rate was 91.3%. Therefore, this study demonstrates the medical application of different PAM in killing cancer cells and promotes the understanding of plasma–liquid interaction. [ABSTRACT FROM AUTHOR]

In plasma cancer therapy, atmospheric pressure plasma jets have attracted increasing attention in recent years. In this study, from the point of view of economic costs and portability, we have employed atmospheric air as the working gas in order to investigate the effects of the rate of flow, applied voltage, frequency, and pulse width on the characteristics of discharge. The concentrations of reactive oxygen and nitrogen species (RONS) in a plasma-activated medium (PAM) were characterized in order to explore their chemical activity. In addition, the inactivating effect of tumor cells induced by an air plasma jet was investigated and the corresponding inactivation mechanism is also discussed. The results showed that the discharge intensity was positively correlated with frequency and voltage, and negatively correlated with pulse width. Regarding the gas flow rate, when the air flow rate was 1 standard liter per minute (SLM), the discharge intensity was strongest according to the length of the plume. By summarizing the discharge characteristics and emission spectra under different experimental parameters, the stable treatment conditions producing rich active substances were as follows: a frequency of 6 kHz, a voltage of 14 kV, a gas flow rate of 1 SLM, and a pulse width of 1 μs. Furthermore, under these stabilized conditions, the air plasma jet produced rich aqueous RONS in a PAM effectively, which killed cells in significant numbers and reduced the cell survival rate. Therefore, this study demonstrates the potential application of an atmospheric PAM for the treatment of tumor cells and promotes a deeper understanding of plasma liquid chemistry. [ABSTRACT FROM AUTHOR]

External static electric and magnetic fields aligned parallel to the propagation direction of a plasma jet affect its dynamic characteristics and the response of reactive species present. A positive electric field was shown to enhance the intensity of ionization waves and the number of positive ions, thereby promoting the generation of aqueous OH and the inactivation of tumor cells subjected to the plasma jet. Correspondingly, the concentration of aqueous O2− and sterilization by the plasma jet gradually increase with increasing negative electric field intensity. The application of an external magnetic field induces a deformation of the plasma plume, manifesting specifically as a radial contraction/expansion of the plasma plume inside/outside the quartz tube because of the influence of magnetic pressure. In addition, with the external magnetic field, the generation of reactive species and the biological inactivation within the plasma jet are improved and can be attributed to the enhanced discharge arising mainly from electrons confined by the axial magnetic field and the radial magnetic pressure. Our work shows that external magnetic fields are well suited to improving the energy efficiency with regard to plasma jet applications, whereas external electric fields provide a means to manipulate the flux and composition of reactive species over the substrate downstream. [ABSTRACT FROM AUTHOR]

Plasma-activated water (PAW) with reactive species produced by plasma in water can efficiently inactivate bacteria and has potential biomedical applications. Surface dielectric barrier discharge (SDBD) is extensively used for the preparation of PAW, and the bactericidal effects of PAW are highly related to the discharge mode. In previous studies, saline was directly placed under surface plasma within a short distance, and the gaseous reactive species diffused into the saline. In this study, the gaseous reactive species flowed into the saline by airflow, which was outside the treatment distance and accelerated the diffusion rate. The gaseous reactive species were compared at different power levels and flow rates, and three discharge modes were classified, namely, ozone, transition, and nitrogen oxides modes, based on the characteristic peaks in the spectra. Long-lived and short-lived species were detected in the saline, and short-lived species were more associated with the bactericidal effect. The results suggest that the bactericidal effect of the transition mode is the most prominent and the scavenger results show that nitric oxide (•NO), singlet oxygen, and peroxynitrite play a more crucial role in bacterial inactivation. This study provides a potential strategy for modulating the discharge mode to generate selective reactive species in plasma-activated saline to promote bactericidal application. [ABSTRACT FROM AUTHOR]

Plasma–liquid interaction is a critical area of plasma science, mainly because much remains unknown about the physicochemical processes occurring at the plasma–liquid interface. Besides a lot of experimental studies toward the interaction, a few fluid models have also been reported in recent years. However, the interfacial boundary conditions in the models are different and the Henry's law constants therein are uncertain; hence, the accuracy and robustness of the simulation results are doubtable. In view of this, three 1D fluid models are developed for the interaction between a plasma jet and deionized water, each of which has a unique interfacial boundary condition as reported in the literature. It is found that the density distribution of reactive species is nearly independent of the interfacial boundary conditions in both the gas and liquid phases, except for that in the interfacial gas layer with a thickness of several tens of micrometers above water. The densities of the reactive species with high Henry's law constants (H > 104) are much different in such gas layers among the interfacial boundary conditions. Moreover, some Henry's law constants are changed in the models according to their uncertainty reported in the literature, and only the reactive species with low Henry's law constants (H < 1) have their aqueous densities following the change. These densities are very low in the plasma-activated water. It could be concluded that the simulation of plasma–liquid interaction is generally independent of the interfacial boundary conditions and the uncertainty in Henry's law constants. [ABSTRACT FROM AUTHOR]

Cold atmospheric plasmas (CAPs) in helium with air gas impurities (He+Air for abbreviation) compromise the discharge stability of helium and the chemical reactivity of air, having great prospects for various applications such as plasma biomedicine. However, different kinds of reactive species are produced in He+Air CAPs but only a few of them could be measured, and the plasma chemistry is so complex that the reported simulation models are simplified to a large extent, such as neglecting the space variation of CAPs by using a 0D model. As a result, much remains unknown for He+Air CAPs, which hinders the development of their applications. For that reason, a 1D fluid model of He+Air CAPs is developed in this paper, incorporating 48 chemical species and 118 volume reactions, which are extracted from a complex chemistry set by a reported 0D model, and then the density distribution of reactive species, the power dissipation pathways, and the chemistry pathways among the reactive species are obtained as a function of air concentration from 500 to 10 000 ppm. It is found that O and NO are the dominant reactive oxygen species (ROS) and reactive nitrogen species (RNS), respectively. Taking the ROS as a whole, it is mainly produced by the electron impact dissociation and excitation of O2; taking the RNS as a whole, it is mainly produced by the oxidation of atomic nitrogen [N and N(2D)], and NO is the precursor for all the other RNS. [ABSTRACT FROM AUTHOR]

The electron energy distribution function (EEDF) of cold atmospheric plasmas (CAPs) is often assumed to be Maxwellian, but it is actually non-Maxwellian, as calculated from the Boltzmann equation. To determine the impact of the Maxwellian assumption, two global models with Maxwellian and non-Maxwellian EEDFs are developed for the He + air CAPs, and the resulting discharge characteristics and reactive species are compared. With the increasing air concentration from 100 to 50 000 ppm in He + air feeding gas, the simulation results of both global models display similar trends, and the orders of the densities of both global models are similar for the reactive species and each air concentration scenario. However, the Maxwellian assumption leads to lower electron temperature, weaker electronegativity, less power dissipation to Ion Joule heating, higher densities, and lagging peak points for most types of reactive species compared to using the non-Maxwellian EEDF. These findings indicate that the Maxwellian assumption is capable of capturing the main physicochemical features of He + air CAPs, but it can lead to large calculation errors at the quantitative level. [ABSTRACT FROM AUTHOR]

A He+Air mixture is a common working gas for cold atmospheric-pressure plasmas which compromises the discharge stability of helium and the chemical reactivity of air. Water vapor is an important component in the gas mixture which can be either introduced as a precursor for reactive species or inevitably entrapped in the plasma system from the surroundings, and the presence of water can cause a profound change on the characteristics of the plasma and consequently its application efficacy. A global model of cold atmospheric-pressure He+Air plasmas is presented in this paper so as to study the influence of humidity. The densities of reactive species and power dissipation are studied as a function of water concentration spanning from 10 to 10 000 ppm. It is found that the dominant cation changes from NO+ to H3O+, and the dominant anion changes from NO2− to OH− with the increasing water concentration. HNO2 and O2(a) are the most abundant reactive nitrogen species and reactive oxygen species, respectively. When the water concentration is above 100 ppm, the electronegativity of the plasma increases dramatically, which has a significant effect on the way of power dissipation in the plasma. Also, the plasma chemistry under different air contents (100, 1000, and 10 000 ppm) is studied as a function of the water concentration. Among different cases of air concentration, the presence of water can enrich the density of most hydrogen-containing species (OH, H2O2, HO2, H3O+, and HNO3) except for HNO2, and it can also enrich the density of hydrogen-free species [O, O3, O2−, and O2(a)] at a low air concentration (100 ppm) while running it down at a high air concentration (1000 and 10 000 ppm). [ABSTRACT FROM AUTHOR]

The understanding of plasma-liquid interactions is of major importance in biomedicine and to better adjust the biological processes induced on/in the biological target by atmospheric pressure plasma jets (APPJs). In order to investigate the physical mechanism of the interaction, the discharge visualization, electrical characteristics, the behavior of bullets dynamics, and the production of reactive oxygen and nitrogen species (RONS) in gas and liquid phases are diagnosed when different working gas APPJs are impinging on liquid. The experimental results show that a small amount of N2 or O2 added in He working gas would significantly change the morphology of jet plume and affect the current amplitude due to the promotion of penning ionization. For bullet propagation, the shape and velocity of the bullet display a huge difference, and it may be strongly dependent on the electric field formed by surface charges deposited on the liquid surface; by comparing touching and not touching the liquid surface, the APPJs impinging on the water illustrate a higher emission intensity of reactive species, particularly OH intensity that is due to the water vapor evaporating into the plasma; for the aqueous RONS (H2O2, NO3−, and NO2−) produced in liquid, it is found that the more the H2O2 production is generated in He + O2 APPJ the higher the NO3− and NO2− concentrations are obtained in He + N2 APPJ. Additionally, the liquid activated by H e + N2 APPJ shows the strongest acidification efficiency due to the more concentrations of HNO3 and HNO2 formation. [ABSTRACT FROM AUTHOR]

Reactive oxygen and reactive nitrogen species (RONS) are believed to play a key role in biomedical applications, which means that RONS must reach the target tissue to produce a therapeutic effect. Existing methods (electron spin spectrometry and microplate reading) to determine the RONS concentration are not suitable for experimental real-time measurements because they require adding an indicating reagent to the plasma-treated medium, which may alter the chemical composition of the medium. In this paper, we propose a method to measure the long-lived RONS concentration in plasma-activated water (PAW) by using UV absorption spectroscopy. Based on an analysis and fit of the absorption spectra of standard solutions (H2O2, NaNO2, and NaNO3), we propose a detailed fitting procedure that allows us to calculate the concentrations of simplex H2O2, NO2−, and NO3−. The results show that the pH and the cross reactivity between RONS in PAW correlate strongly with the absorption spectra. To confirm the accuracy of the calculations, we also use a microplate reader and add chemical reagents to measure the concentrations of H2O2, NO2−, and NO3−. The results show that the concentrations calculated by the proposed fitting method are relatively accurate and that the error range is acceptable. Additionally, the time-dependent diffusion of RONS in PAW is measured and analyzed at different depths in the PAW. This fitting approach constitutes a nonintrusive approach to measure RONS at different depths in PAW. [ABSTRACT FROM AUTHOR]

He + O2 plasma jets in open air and in an airtight chamber are comparatively studied, with respect to their production of gaseous/aqueous reactive species and their antibacterial effects. Under the same discharge power, the plasma jet in open air has higher densities of gaseous reactive species and a higher concentration of aqueous H2O2 but lower concentrations of aqueous OH and O2-. In addition, the increase in the O2 ratio in He in both plasma jets causes a linear decrease in the population of gaseous reactive species, except for O(3p5P) when a small amount of O2 is added to the working gas. The concentrations of aqueous reactive species for OH and H2O2 also drop monotonically with the increase in additive O2, while the aqueous O2- first increases and then decreases. Moreover, it is interesting that the bactericidal inactivation in the airtight chamber condition is much greater than that in the open air condition regardless of the presence or absence of additive O2 in the He plasma jet. The concentration trends of O2- for both the plasma jets are similar to their antibacterial effects, and little antibacterial effect is achieved when a scavenger of O2- is used, indicating that O2- should be a main antibacterial agent. Moreover, it should not be O2- alone to achieve the antibacterial effect, and some reactive nitrogen species such as ONOO- and O2NOO- might also play an important role. [ABSTRACT FROM AUTHOR]

Cold atmospheric plasma (CAP) is a rapidly developed technology that has been widely applied in biomedicine especially in cancer treatment. Due to the generation of various active species in plasma, CAP could induce various tumor cells death and showed a promising potential in cancer therapy. To enhance the biological effects of gas plasma, changing the discharging parameters is the most commonly used method, yet increasing discharging power will lead to a higher possibility of simultaneously damage surrounding tissues. In this study, by adding nontoxic concentration of additional nitrite and nitrate in the medium, we found that anti-tumor effect of CAP treatment was enhanced in the same discharging parameters. By microplate reader and cell flow cytometer we measured several extracellular and intracellular RONS and found that ONOO- was mostly correlated with the enhanced cancer cell killing effect. We proposed that more nitrogen supplies such as nitrite and nitrate could increase the production of RNS especially ONOO- and resulted in a better killing effect to cancer cells. Our results provided a new strategy to enhance the antitumor effect by plasma jet treatment without changing the discharging parameters. [ABSTRACT FROM AUTHOR]

In this paper, a one-dimensional fluid model of He + O2 dielectric barrier discharge is established. As the oxygen concentration increases from 0.2% to 0.7% and 1.2%, the plasma transforms from triple-breakdowns to single-breakdown per half-cycle. In the mode of multi-breakdowns, the first pulse produces more particles although dissipates more power, thus making remarkable differences in the energy efficiencies in producing charged species but can hardly affect neutral species. We also operate the model in another way that the plasma is held in the mode of single-breakdown, by changing the oxygen concentration and voltage amplitude at the same time, so the impact of mode transformation is removed. In this way, the production efficiency of the electron decreases significantly, probably owing to the enhanced electron attachment with O2 and O3. After analyzing the main chemistry process of both charged and neutral species, it is suggested that the decreasing efficiency of the electron and the increasing oxygen concentration impose opposite impacts on the energy efficiencies of other species. Almost all charged species decrease more or less in their efficiencies, but O3- is the exception. For neutral species, the efficiencies vary slightly for O and O* but increase more than 250% for O2* and O3. [ABSTRACT FROM AUTHOR]

Helium-oxygen dielectric barrier discharge has received much attention due to its high efficiency and stability in producing reactive oxygen species (ROS). Previous studies evidenced that the dielectric-barrier controlled plasma would transform from single-breakdown to multi-breakdowns per half cycle with the increasing applied voltage, but the variation of densities and wall fluxes of ROS during the transformation has not been well understood. This motivates us to construct a one-dimensional fluid model for this study. The results show that the volume-averaged densities and wall fluxes of the electron, ions, and atomic metastables are temporally pulsed with each breakdown, but they are nearly invariable for the grounded neutrals (O and O3) and molecular metastables [such as O2(a1Δg)]. For each species, the temporal pulses of density and flux of a specific species have different widths, and the widths remain almost constant in time among the breakdowns except for that of the electron. With the increasing number of breakdowns per half cycle, the wall fluence and the peak value of temporal flux pulses of O− have obviously different trends, and the energy efficiencies for the production and wall fluence increase significantly only for O− and O3−. [ABSTRACT FROM AUTHOR]

In this paper atmospheric-pressure rf He+O2 cold plasmas are studied by means of a 1-D fluid model. 17 species and 60 key reactions selected from a study of 250+ reactions are incorporated in the model. O2+, O3-, and O are the dominant positive ion, negative ion, and reactive oxygen species, respectively. Ground state O is mainly generated by electron induced reactions and quenching of atomic and molecular oxygen metastables, while three-body reactions leading to the formation of O2 and O3 are the main mechanisms responsible for O destruction. The fraction of input power dissipated by ions is ∼20%. For the conditions considered in the study ∼6% of the input power is coupled to ions in the bulk and this amount will increase with increasing electronegativity. Radial and electrode losses of neutral species are in most cases negligible when compared to gas phase processes as these losses are diffusion limited due to the large collisionality of the plasma. The electrode loss rate of neutral species is found to be nearly independent of the surface adsorption probability p for p > 0.001 and therefore plasma dosage can be quantified even if p is not known precisely. [ABSTRACT FROM AUTHOR]

In plasma cancer therapy, the inactivation of cancer cells under plasma treatment is closely related to the reactive oxygen and nitrogen species (RONS) induced by plasmas. Quantitative study on the plasma-induced RONS that related to cancer cells apoptosis is critical for advancing the research of plasma cancer therapy. In this paper, the effects of several reactive species on the inactivation of LP-1 myeloma cancer cells are comparatively studied with variable working gas composition, surrounding gas composition, and discharge power. The results show that helium plasma jet has a higher cell inactivation efficiency than argon plasma jet under the same discharge power. By comparing the concentration of aqueous phase reactive species and the cell inactivation efficiency under different working gases and discharge powers, it is demonstrated that the inactivation efficiency of LP-1 myeloma cancer cells is strongly correlated with the concentration of peroxynitrite (ONOOH/ONOO−). [ABSTRACT FROM AUTHOR]

Comparisons between pulsed and sinusoidal plasma jets have been extensively reported for the discharge characteristics and gaseous reactive species, but rarely for the aqueous reactive species in water solutions treated by the two types of plasma jets. This motivates us to compare the concentrations of aqueous reactive species induced by a pulsed and a sinusoidal plasma jet, since it is widely reported that these aqueous reactive species play a crucial role in various plasma biomedical applications. Experimental results show that the aqueous H2O2, OH/O2−, and O2−/ONOO− induced by the pulsed plasma jet have higher concentrations, and the proportional difference increases with the discharge power. However, the emission intensities of OH(A) and O(3p5P) are higher for the sinusoidal plasma jet, which may be attributed to its higher gas temperature since more water vapor could participate in the plasma. In addition, the efficiency of bacterial inactivation induced by the pulsed plasma jet is higher than that for the sinusoidal plasma jet, in accordance with the concentration relation of aqueous reactive species for the two types of plasma jets. [ABSTRACT FROM AUTHOR]

In this paper, we present the effects of the pulse width (PW) on the plasma jet's discharge characteristics, particularly focusing on the production and correlation of the reactive oxygen and nitrogen species (RONS) in gas- and liquid-phase. It is found that the length of plasma jet plume first increases before the PW of 10 μs, then gradually decreases and finally almost remains unchanged beyond 150 μs. The plasma bullet disappears after the falling edge of the voltage pulse at low PW, while it terminates far ahead of the falling edge of voltage pulse at high PW. This is mainly attributed to accumulation of space charges that lead to weakening of the reduced electric field with an increase of PW from low to high. More important, it is found that the excited reactive species, the positive and negative ions from plasma jet, and the concentrations of NO2– and NO3– in deionized water exposed to plasma jet also display the first increasing and then decreasing change trend with increase of PW, while the concentration of H2O2 in water almost displays the linearly increasing trend. This mainly results from the formation of the H3O+ and HO2–, as well as their ion water clusters that can produce more OH radicals to be converted into H2O2, while the NO2– and NO3– in gas phase can transport into water and exist most stably in water. The water cluster formation at gas-liquid interface is an important key process that can affect the chemical nature and dose of aqueous RONS in water; this is beneficial for understanding how the RONS are formed in liquid-phase. [ABSTRACT FROM AUTHOR]

Cold atmospheric plasma (CAP) is a rapidly developed technology that has been widely applied in biomedicine especially in cancer treatment. Due to the generation of various active species in plasma, CAP could induce various tumor cells death and showed a promising potential in cancer therapy. To enhance the biological effects of gas plasma, changing the discharging parameters is the most commonly used method, yet increasing discharging power will lead to a higher possibility of simultaneously damage surrounding tissues. In this study, by adding nontoxic concentration of additional nitrite and nitrate in the medium, we found that anti-tumor effect of CAP treatment was enhanced in the same discharging parameters. By microplate reader and cell flow cytometer we measured several extracellular and intracellular RONS and found that ONOO- was mostly correlated with the enhanced cancer cell killing effect. We proposed that more nitrogen supplies such as nitrite and nitrate could increase the production of RNS especially ONOO- and resulted in a better killing effect to cancer cells. Our results provided a new strategy to enhance the antitumor effect by plasma jet treatment without changing the discharging parameters. [ABSTRACT FROM AUTHOR]