Guimin Xu

Chemical Mechanisms of Bacterial Inactivation Using Dielectric Barrier Discharge Plasma in Atmospheric Air

Nonthermal plasma generated by parallel-plate dielectric-barrier discharge with 60-kHz high-voltage power was used to sterilize the bacteria in atmospheric air. Two kinds of typical bacteria, gram-negative E. coli (ATCC8099) and grampositive S. aureus (ATCC6538), were used as test strains. Bacteria cells held by cover-glass were placed on the bottom electrode. By adjusting the applied voltage, gap spacing, and treatment time, the effects of plasma and electric field on bacteria inactivation were investigated. The transmission electron microscope was used to observe the damage of cells treated by plasma. The concentrations of K+, protein, and nucleic acid leaked from cells were measured for detecting the cytoplasm status after plasma treatment. Experimental results showed that almost 100% of S. aureus and E. coli strains were killed in less than 10- and 7-s plasma treatment, respectively. It is concluded that the reactive oxygen species (ROS) in plasma play a dominant role in the inactivation process but not the electric field. It is supposed that the ROS can oxidize the cell membrane and then damage the protein and nucleic acid inside the cells and, thus, kill the bacteria.

DBD Plasma Jet in Atmospheric Pressure Argon

Nonthermal plasma jet was generated by dielectric barrier discharge (DBD) with a 34-kHz sinusoidal power supply in argon. The power consumption ranged from several to tens of watts. The flow rate of argon, which was detected by an anemometer, greatly affected the discharge images. The gas flow temperature of the DBD plasma was measured with a thermocouple, and it was shown that, when the flow rate of argon was relatively high, its temperature was similar to room temperature and the plasma jet indicated the glow discharge characteristics. The low-temperature plasma jet is suitable for medical sterilization and surface modification of materials with irregular shapes.

Research on Surface Modification of Polytetrafluoroethylene Coupled With Argon Dielectric Barrier Discharge Plasma Jet Characteristics

An argon dielectric barrier discharge (DBD) atmospheric-pressure plasma jet (APPJ) is designed and employed for surface modification of polytetrafluoroethylene (PTFE). The plasma diagnostics and dielectric surface analysis are coupled together to investigate the mechanisms of plasma modification. The discharge power is obtained by Lissajous figure, and electron excitation temperature (EET) is measured through an optical emission spectrum and calculated by a Boltzmann diagrammatic method. The surface properties of modified PTFE samples are characterized by the static contact angle, surface resistivity, scanning electron microscope (SEM), and X-ray photoelectron spectroscopy. The results show that the discharge power, EET, and surface wettability increase with the Ar flowing rate, and a slight decrease of surface resistivity is revealed after plasma treatment. The surface roughness of PTFE is enhanced, and the oxygen-containing hydrophilic groups are incorporated by the impacts of APPJ radical species. Moreover, the hydrophilicity of PTFE can be improved by a surface presanding process, particularly after APPJ treatment. Finally, the surface modification mechanisms of APPJ on PTFE are discussed.

Dual effects of atmospheric pressure plasma jet on skin wound healing of mice.

Cold plasma has become an attractive tool for promoting wound healing and treating skin diseases. This article presents an atmospheric pressure plasma jet (APPJ) generated in argon gas through dielectric barrier discharge, which was applied to superficial skin wounds in BALB/c mice. The mice (n = 50) were assigned randomly into five groups (named A, B, C, D, E) with 10 animals in each group. Natural wound healing was compared with stimulated wound healing treated daily with APPJ for different time spans (10, 20, 30, 40, and 50 seconds) on 14 consecutive days. APPJ emission spectra, morphological changes in animal wounds, and tissue histological parameters were analyzed. Statistical results revealed that wound size changed over the duration of the experimental period and there was a significant interaction between experimental day and group. Differences between group C and other groups at day 7 were statistically significant (p < 0.05). All groups had nearly achieved closure of the untreated control wounds at day 14. The wounds treated with APPJ for 10, 20, 30, and 40 seconds showed significantly enhanced daily improvement compared with the control and almost complete closure at day 12, 10, 7, and 13, respectively. The optimal results of epidermal cell regeneration, granulation tissue hyperplasia, and collagen deposition in histological aspect were observed at day 7. However, the wounds treated for 50 seconds were less well healed at day 14 than those of the control. It was concluded that appropriate doses of cold plasma could inactivate bacteria around the wound, activate fibroblast proliferation in wound tissue, and eventually promote wound healing. Whereas, over doses of plasma suppressed wound healing due to causing cell death by apoptosis or necrosis. Both positive and negative effects may be related to the existence of reactive oxygen and nitrogen species (ROS and RNS) in APPJ.

Research on the Inactivation Effect of Low-Temperature Plasma on Candida Albicans

A dielectric barrier discharge was used to generate low-temperature plasma to treat Candida albicans. When the gap spacing was 3 mm, the killing log value (KLV) of the plasma on Candida albicans within 20 s of exposure was more than five, and for 4 and 5 mm gap spacing, the KLV within 25 s was more than five. With the extension of exposure time, the decrease in velocity of the number of living Candida albicans was fastest for the gap spacing of 3 mm, and then for 4 and 5 mm spacing. With 60 s of electric field treatment, as the applied voltage increases, the survival number of Candida albicans has no significant difference from that of the control sample. As for the inactivation mechanism of plasma on Candida albicans on the molecular microbiology side, transmission electron microscopic examination and the results of protein, nucleic acid and K+ detection in the extracellular environment showed that the plasma destroyed the outer structure of Candida albicans. Cytoplasm was also released, which caused Candida albicans to be dead. On the plasma physics side, the role of the electric field during Candida albicans inactivation by plasma is considered negligible. Therefore, charged particles and reactive species in plasma might play a dominant role in the process of destroying the outer structure of Candida albicans.

Behaviors of Plasma Bullet Propagation and Effects of Gas Flow Rate

An Ar dielectric-barrier-discharge atmospheric-pressure plasma jet (APPJ) driven by a 34-kHz sinusoidal power source is employed to investigate plasma bullet propagation in positive and negative half cycles by using an intensified charge-coupled device camera. The effects of different Ar gas flow rates on plasma bullet behavior are also presented in this paper. It is found that the duration and velocity of bullets in a positive discharge current pulse are significantly shorter and faster than those in a negative discharge current pulse and APPJ seems easier to form the plasma bullet phenomena during the positive discharge current pulse. The differences between positive and negative discharge current pulses can be explained by using the cathode-directed streamer and negative corona theories, respectively. It is considered that, due to the possible turbulence flow, the propagation length of plasma bullets is decreased with the increment of gas flow rates.

Experimental Research on Mode Transitions of Atmospheric Pressure Helium Dielectric Barrier Discharge

The discharge mode transitions and the characteristics of atmospheric pressure dielectric barrier discharge in pure helium (He-DBD) are studied. Different discharge modes of He-DBD are clarified, including filament-diffuse mixed mode, filamentary mode, diffuse mode, and multichannels coupled mode. The transitions of different modes are explored by changing the gap width and applied voltage. According to the luminous structure of discharge [short exposure (100~300 ns) image], it is found that there should be only Townsend-like and glow-like discharges that appear in the above modes. In Townsend-like discharge, the secondary electron emission coefficient (SEEC) of dielectric is estimated. Based on which, a fluid model coupled with an external circuit is built to explain the He-DBD mode transitions mechanism and the applied voltage drops influence on He-DBD. Through the temporal evolution of a luminous structure, a discharge filament is believed to be a contractive state of discharge channel, which should be an unstable glow-like discharge. The radius of discharge channel, changing with gap width and applied voltage, is measured. The discharge contraction is attributed to the nonlinear relationship between Townsend ionization coefficient and electric field. The enhancing interaction between different discharge channels inhibits the appearing of diffuse discharge around discharge filament, leading to the transition from mixed mode to filamentary mode. In the end, the multichannels coupled mode is proven to be glow-like discharge, and its formation mechanism is explained by the overlap of discharge channels.

Investigation on the characteristics of dielectric barrier discharge in methane with parallel-plate and multi needle-plate electrode in low pressure

Summary form only given. Non-equilibrium plasma-assisted combustion has been extensively studied over the last few decades and has shown promising effects on combustion controlling, such as reducing ignition delay time, increasing flame propagation speed, enhancing flame stabilization and so on. In this paper, we investigated on the characteristics of dielectric barrier discharge (DBD) in methane with parallel-plate and multi-needle-to-plate electrodes under low pressure with sinusoidal waveform (20 kHz, 0-30 kV) power supply. A mechelle spectrometer (Mechelle 5000, Andor) is used to capture the plasma spectra. The results show that the discharge produces abundant active components related to combustion, such as CH (λ=392.5, 430.1, 438.7, 440.9nm), and C2 (A=473.6nm) in the excited level. Temperature of the active particles is calculated by LIFBASE software and platinum-rhodium thermocouple. With the increasing of applied voltage, the gas temperature and the number and average energy of the high-energy electrons are increased, leading to more free particles which are in the excited state, and finally the corresponding emission spectrum intensity is enhanced. Under the same gas pressure and electrode gap except for generation by different the electrode structure, the temperature of gas in multi needle-plate electrode is lower than plate-plate electrode. And it is proven that multi needles in a honeycomb structure layout can be made in more stable discharge, which can be used in sub-atmospheric even under atmospheric pressure, and it is better for plasma-assisted combustion application.

Low temperature plasma promoting fibroblast proliferation by activating the NF-κB pathway and increasing cyclinD1 expression

The potential applications of low temperature plasma (LTP) in wound healing have aroused the concern of many researchers. In this study, an argon atmospheric pressure plasma jet was applied to generate LTP for treatment of murine fibroblast cell (L929) cultured in vitro to investigate the effect of NF-κB pathway on fibroblast proliferation. The results showed that, compared with the control, L929 cells treated with plasma for less than 20 s had significant increases of proliferation; the productions of intracellular ROS, O2− and NO increased with prolongation of LTP treatment time; NF-κB pathway was activated by LTP in a proper dose range, and the expression of cyclinD1 in LTP-treated cells increased with the same trend as cell proliferation. After RNA interference to block p65 expression, with the same treatment time, RNAi-treated cells proliferated more slowly and expressed less cyclinD1 than normal cells. Furthermore, pretreatment with N-acetyl-L-cysteine (NAC) markedly prevented the plasma-induced changes in cells. In conclusion, the proliferation of L929 cells induced by LTP was closely related to NF-κB signaling pathway, which might be activated by appropriate level of intracellular ROS. These novel findings can provide some theoretical reference of LTP inducing cell proliferation and promoting wound healing.

Effects of atmospheric pressure plasma jet with floating electrode on murine melanoma and fibroblast cells

Atmospheric pressure cold plasma jets have been recently shown as a highly promising tool in certain cancer therapies. In this paper, an atmospheric pressure plasma jet (APPJ) with a one inner floating and two outer electrode configuration using helium gas for medical applications is developed. Subjected to a range of applied voltages with a frequency of 19.8 kHz at a fixed rate of gas flow (i.e., 3 l/min), electrical and optical characteristics of the APPJ are investigated. Compared with the device only with two outer electrodes, higher discharge current, longer jet, and more active species in the plasma plume at the same applied voltage together with the lower gas breakdown voltage can be achieved through embedding a floating inner electrode. Employing the APPJ with a floating electrode, the effects of identical plasma treatment time durations on murine melanoma cancer and normal fibroblast cells cultured in vitro are evaluated. The results of cell viability, cell apoptosis, and DNA damage detection sho...