Control of multidrug-resistant planktonic Acinetobacter baumannii: biocidal efficacy study by atmospheric-pressure air plasma

In this research,an atmospheric-pressure air plasma is used to inactivate the multidrug-resistant Acinetobacter baumannii in liquid.The efficacy of the air plasma on bacterial deactivation and the cytobiological variations after the plasma treatment are investigated.According to colony forming units,nearly all the bacteria (6-log) are inactivated after 10 min of air plasma treatment.However,7％ of the bacteria enter a viable but non-culturable state detected by the resazurin based assay during the same period of plasma exposure.Meanwhile,86％ of the bacteria lose their membrane integrity in the light of SYTO 9/PI staining assay.The morphological changes in the cells are examined by scanning electron microscopy and bacteria with morphological changes are rare after plasma exposure in the liquid.The concentrations of the long-living RS,such as H2O2,NO3,and O3,in liquid induced by plasma treatment are measured,and they increase with plasma treatment time.The changes of the intracellular ROS may be related to cell death,which may be attributed to oxidative stress and other damage effects induced by RS plasma generated in liquid.The rapid and effective bacteria inactivation may stem from the RS in the liquid generated by plasma and air plasmas may become a valuable therapy in the treatment of infected wounds.     

The mechanism study of low-pressure air plasma cleaning on large-aperture optical surface unraveled by experiment and reactive molecular dynamics simulation

Low-pressure air plasma cleaning is an effective method for removing organic contaminants on large-aperture optical components in situ in the inertial confinement fusion facility. Chemical reactions play a significant role in plasma cleaning, which is a complex process involving abundant bond cleavage and species generation. In this work, experiments and reactive molecular dynamics simulations were carried out to unravel the reaction mechanism between the benchmark organic contaminants of dibutyl phthalate and air plasma. The optical emission spectroscopy was used to study the overall evolution behaviors of excited molecular species and radical signals from air plasma as a reference to simulations. Detailed reaction pathways were revealed and characterized, and specific intermediate radicals and products were analyzed during experiments and simulation. The reactive species in the air plasma, such as O, HO₂ and O₃ radicals, played a crucial role in cleaving organic molecular structures. Together, our findings provide an atomic-level understanding of complex reaction processes of low-pressure air plasma cleaning mechanisms and are essential for its application in industrial plasma cleaning.     

Review on reactive species in water treatment using electrical discharge plasma: formation,measurement, mechanisms and mass transfer

In the electrical discharge plasma process, various chemical and physical processes can participate in the removal of contaminants. In this paper, the chemical and physical processes that occur as a result of the electrical discharge plasma are reviewed, and their possible roles in the degradation of contaminants are discussed. Measurement methods for the quantification of important reactive species and their advantages and shortcomings are presented. Approaches on how to enhance the diffusion of the reactive species in solution are examined. In addition, the formation of typical reactive species in different electrical discharge plasma is compared.     

The effect of gas additives on reactive species and bacterial inactivation by a helium plasma jet

In this paper,the influences of gas doping(O_2,N_2,Air)on the concentrations of reactive species and bactericidal effects induced by a He plasma jet are studied.Firstly,results show that gas doping causes an increase in voltage and a decrease in current compared with the pure He discharge under the same discharge power,which might be attributed to the different chemical characteristics of O_2 and N_2 and verified by the changes in the gaseous reactive species shown in the optical emission spectroscopy(OES) and Fourier transform infrared(FTIR)spectroscopy.Secondly,the concentrations of aqueous reactive oxygen species(ROS) and reactive nitrogen species(RNS) are tightly related to the addition of O_2 and N_2 into the working gas.The concentrations of aqueous NO_2~- and NO_3~- significantly increase while the concentrations of aqueous ROS decrease with the admixture of N_2.The addition of O_2 has little effect on the concentrations of NO_2~- and NO_3~- and pH values; however,the addition of O_2 increases the concentration of O_2~- and deceases the concentrations of H_2O_2 and OH.Finally,the results of bactericidal experiments demonstrate that the inactivation efficiency of the four types of plasma jets is He?+?O_2??He+AirHeHe+N_2,which is in accordance with the changing trend of the concentration of aqueous O_2~-.Simultaneously to the better understanding of the formation and removal mechanisms of reactive species in the plasma–liquid interaction,these results also prove the effectiveness of regulating the concentrations of aqueous reactive species and the bacteria inactivation effects by gas doping.     

A numerical simulation study on active species production in dense methane-air plasma discharge

Recently, low-temperature atmospheric pressure plasmas have been proposed as a potential type of ‘reaction carrier' for the conversion of methane into value-added chemicals. In this paper, the multi-physics field coupling software of COMSOL is used to simulate the detailed discharge characteristics of atmospheric pressure methane-air plasma. A two-dimensional axisymmetric fluid model is constructed, in which 77 plasma chemical reactions and 32 different species are taken into account. The spatial density distributions of dominant charged ions and reactive radical species, such as CH_4~+CH_3~+N_2~+O_2~+H, O, CH_3, and CH_2, are presented, which is due to plasma chemical reactions of methane/air dissociation(or ionization) and reforming of small fragment radical species. The physicochemical mechanisms of methane dissociation and radical species recombination are also discussed and analyzed.     

Study of generation characteristics of glow-type atmospheric-pressure plasma jet based on DC discharge in air

In order to form an atmospheric-pressure plasma jet without airflow, a needle–ring electrode structure is proposed in this paper. When heteropolar potentials are applied to a needle and a ring, a marked electric field strength enhancement around the needle's pointed end has been found. When the same potential is applied to both the needle and the ring, the lateral electric field strength for the needle can be weakened. By using the above two methods, an increase of the difference between the pointed end electric field strength and the lateral one is achieved and stable plasma jets are formed. A symmetrical space electric field distribution is established at the pointed end of the needles when several sets of heteropolar needle–ring electrodes are uniformly arranged, which is conducive to forming a uniform array plasma jet. Under DC discharge conditions, a safe and stable plasma jet of high density and an array plasma jet are successfully achieved.     

Influence of Ti3C2Tx(MXene)on the generation of dielectric barrier discharge in air

The formation of homogeneous dielectric barrier discharge(DBD)in air is a key scientific problem and core technical problem to be solved for the application of plasmas.Here,we report the effect of two-dimensional(2D)nanomaterial Ti3C2Tx(Tx=-F,-O and/or-OH)on regulating the electrical discharge characteristics.The field emission and weak bound state property of Ti3C2Tx can effectively increase the seed electrons and contribute to the generation of atmospheric pressure homogeneous air DBD.The electron avalanche development for the uneven electrode structure is calculated,and the discharge mode transition is modeled.The comparative analyses of discharge phenomena validate the regulation of Ti3C2Tx on the discharge characteristics of DBD.The light emission capture and the voltage and current waveforms verify that the transition of Townsend discharge to streamer discharge is effectively inhibited.The optical emission spectra are used to characterize the plasma and confirm that it is in a non-equilibrium state and the gas temperature is at room temperature.This is the first exploration of Ti3C2Tx on the regulation of electrical discharge characteristics as far as we know.This work proves the feasibility of Ti3C2Tx as a source of seed electrons to form homogeneous DBD,establishing a preliminary foundation for promoting the application of atmospheric pressure non-equilibrium plasma.     

Generation of reactive species in atmospheric pressure dielectric barrier discharge with liquid water

Atmospheric pressure helium/water dielectric barrier discharge(DBD) plasma is used to investigate the generation of reactive species in a gas–liquid interface and in a liquid. The emission intensity of the reactive species is measured by optical emission spectroscopy(OES)with different discharge powers at the gas–liquid interface. Spectrophotometry is used to analyze the reactive species induced by the plasma in the liquid. The concentration of OH radicals reaches 2.2 μm after 3 min of discharge treatment. In addition, the concentration of primary longlived reactive species such as H_2O_2, NO_3~- and O_3 are measured based on plasma treatment time.After 5 min of discharge treatment, the concentration of H_2O_2, NO_3~-, and O_3 increased from 0 mg?·?L~(-1) to 96 mg?·?L~(-1), 19.5 mg?·?L~(-1), and 3.5 mg?·?L~(-1), respectively. The water treated by plasma still contained a considerable concentration of reactive species after 6 h of storage. The results will contribute to optimizing the DBD plasma system for biological decontamination.     

Applications of atmospheric pressureplasma in microbial inactivation and cancertherapy: a brief review

Atmospheric pressure cold plasma, with advantages such as high particle activity, no thermaldamage, high efficiency and direct and friendly contact with human tissues, is considered to havegreat potential in biomedical applications. Therefore, ‘plasma medicine’ as a new interdisciplinehas been developed in the past two decades. This review first briefly describes the developmentof typical plasma sources suitable for biomedical applications, and those with different dischargeforms are simply compared, evaluated and summarized. Subsequently, measurement of thecrucial gaseous reactive particles (e.g. OH and O) and their spatio-temporal distributions areintroduced. Meanwhile, the generation and variation rules and the related critical macroscopicparameters of the plasma-induced aqueous reactive species are summarized. Finally, relatedstudies in the last ten years on the mechanisms of the plasma-driven microbial inactivation andplasma-induced apoptosis of cancer cells are introduced. Moreover, some scientific problemsthat need to be urgently solved in the field of plasma medicine are also discussed. This reviewwill provide useful guidance for future related research.     

Characteristics of DBD micro-discharge at different pressure and its effect on the performance of oxygen plasma reactor

The oxygen plasma reactor based on dielectric barrier discharge principle can produce a high concentration of reactive oxygen species, which can cooperate with hydraulic cavitation gas–liquid mixer to realize the application of advanced oxidation technology in water treatment. In this technology, the work pressure of the oxygen plasma reactor is decreased by the vacuum suction effect generated in the snap-back section of the gas–liquid mixed container. In this paper, the characteristics of single micro-discharge at different pressures were investigated with the methods of discharge image, electrical characteristics and spectral diagnosis, in order to analyze the electrical characteristics and reactive oxygen species generation efficiency of oxygen plasma reactor at the pressure range from 60 kPa to 100 kPa. The study indicated that, when the pressure decreases, the duty ratio of ionization in the discharge gap and number of electrons with high energy increases, leading to a rise in reactive oxygen species production. When the oxygen reaches the maximum ionization, the concentration of reactive oxygen species is the highest. Then, the discharge intensity continues to increase, producing more heat, which will decompose the ozone and lower the production of reactive oxygen species. The oxygen plasma reactor has an optimum working pressure at different input powers, which makes the oxygen plasma reactor the most efficient in generating reactive oxygen species.     

铀氢锆堆中子源辐照含硼C6胶质瘤细胞的生物学效应研究

利用蒙卡程序MCNP／4B(Monte Carlo N-particle transportcode／4B)设计了C6细胞辐照实验的铀氢锆堆中子源。建立了细胞培养、孵育、L-BPA(L-boron phenylalanine)给药、细胞内宏观硼浓度测定及辐照实验方法，观察了BNCT(Boron neutron capture therapy)辐照实验对体外C6胶质瘤细胞的放射生物学效应，研究了C6细胞BNCT辐照效应与照射剂量之间的关系。试验结果表明，在同等吸收剂量下，BNCT对C6细胞的杀伤作用远远大于γ射线。     

Numerical investigation on electron effects in the mass transfer of the plasma species in aqueous solution

The objective of this work is to contribute an understanding of the effects of electrons in the plasmas on the mass transfer of plasma species in aqueous solution by means of the numerical simulation based on a one-dimensional diffusion-reaction model. The plasma species are divided into two groups, i.e. electrons and the other species, and the mass transfer in the three scenarios has been simulated, including the systematic calculations of the depth distributions of five major reactive species, OH, O₃, HO₂ , O₂^-, and H₂O₂ . In the three scenarios, the particles considered to enter into aqueous solution are all the plasma species (the scenario I, where the mass transfer of plasma species is a result due to the synergy of the electrons and the other plasma species), the other species (the scenario II), and only electrons in plasma species (the scenario III), respectively. The detailed analyses on the difference between the depth distributions of each reactive species in these three scenarios show the following conclusions. The electrons play an important role in the mass transfer of plasma species in aqueous solution and the synergy of the electrons and the other plasma species (the electron-species synergy) presents its different effects on the mass transfer. The vast majority of H₂O₂ are generated from a series of the electron- related reactions in aqueous solution, which is hardly affected by the electron-species synergy. Compared to the results when only the electrons enter into the liquid region, the electron-species synergy evidently weakens the generation of O₂^-, O₃ , and OH, but promotes to produce HO₂ .     

Analysis of the critical active species for methylene blue decoloration in a dielectric barrier discharge plasma system

In the paper, a hybrid gas–liquid dielectric barrier discharge (DBD) plasma system was set up to treat a methylene blue (MB) solution. The effects of the change of the carrier gas, the gas bubbling rate and different kinds of scavenger addition, including sodium carbonate (Na₂CO₃), para benzoquinone (p-BQ), triethylenediamine and sodium dihydrogen phosphate (NaH₂PO₄), on the MB decoloration were reviewed to clarify the critical active species for the dye decoloration in the DBD plasma system. The obtained results show that higher decoloration of the MB solution could be achieved when O₂ was used as the carrier gas, which could be 100% after 20 min discharge treatment, and the result confirmed the crucial effect of O₃ in the MB decoloration. Based on the experiments of the scavenger addition, it could be concluded that O₂⁻ and ¹O₂ were two other important reactive oxygen species (ROS) for the MB decoloration. The results of the higher chemical oxygen demand removal and faster disappearance of the characteristic peak of the MB from the UV–vis analysis under O₂ bubbling conditions also proved the critical effect of the ROS formed by O₂ on the MB decoloration.     

用41Ca-AMS法测定谷氨酸毒性对PC12细胞外钙内流的影响

本工作用41Ca示踪PC12细胞,以CaF2作为最终测量样品,用加速器质谱计(全称AMS)测量41Ca.从谷氨酸毒性对PC12细胞的时间效应,MK-801对PC12细胞受体门控钙通道(全称ROC)阻断效应两方面进行分析,以激光扫描共聚焦显微镜的检测结果作为参照,结果表明41Ca的加速器质谱(AMS)测量方法能有效地检测到在不同情况下谷氨酸引起PC12细胞中外钙内流的情况.综合两种方法推测在谷氨酸引起的钙超载中,NMDAR介导的外钙内流起了重要作用.