Eun H. Choi

Altered antioxidant system stimulates dielectric barrier discharge plasma-induced cell death for solid tumor cell treatment.

This study reports the experimental findings and plasma delivery approach developed at the Plasma Bioscience Research Center, Korea for the assessment of antitumor activity of dielectric barrier discharge (DBD) for cancer treatment. Detailed investigation of biological effects occurring after atmospheric pressure non-thermal (APNT) plasma application during in vitro experiments revealed the role of reactive oxygen species (ROS) in modulation of the antioxidant defense system, cellular metabolic activity, and apoptosis induction in cancer cells. To understand basic cellular mechanisms, we investigated the effects of APNT DBD plasma on antioxidant defense against oxidative stress in various malignant cells as well as normal cells. T98G glioblastoma, SNU80 thyroid carcinoma, KB oral carcinoma and a non-malignant HEK293 embryonic human cell lines were treated with APNT DBD plasma and cellular effects due to reactive oxygen species were observed. Plasma significantly decreased the metabolic viability and clonogenicity of T98G, SNU80, KB and HEK293 cell lines. Enhanced ROS in the cells led to death via alteration of total antioxidant activity, and NADP+/NADPH and GSH/GSSG ratios 24 hours (h) post plasma treatment. This effect was confirmed by annexin V-FITC and propidium iodide staining. These consequences suggested that the failure of antioxidant defense machinery, with compromised redox status, might have led to sensitization of the malignant cells. These findings suggest a promising approach for solid tumor therapy by delivering a lethal dose of APNT plasma to tumor cells while sparing normal healthy tissues.

Influence of secondary electron emission on breakdown voltage in a plasma display panel

A measurement of the secondary electron-emission coefficient γ from MgO film in a plasma display panel is carried out. The influence of the secondary electron emission on the breakdown voltage in microdischarges on the plasma display panel is investigated by making use of the Townsend sparking criterion. Experimental data agree well with theoretical results, verifying the previous theoretical model.

Differential Epigenetic Effects of Atmospheric Cold Plasma on MCF-7 and MDA-MB-231 Breast Cancer Cells.

Cold atmospheric plasma (plasma) has emerged as a novel tool for a cancer treatment option, having been successfully applied to a few types of cancer cells, as well as tissues. However, to date, no studies have been performed to examine the effect of plasma on epigenetic alterations, including CpG methylation. In this study, the effects of plasma on DNA methylation changes in breast cancer cells were examined by treating cultured MCF-7 and MDA-MB-231 cells, representing estrogen-positive and estrogen-negative cancer cells, respectively, with plasma. A pyrosequencing analysis of Alu indicated that a specific CpG site was induced to be hypomethylated from 23.4 to 20.3% (p < 0.05) by plasma treatment in the estrogen-negative MDA-MB-231 cells only. A genome-wide methylation analysis identified “cellular movement, connective tissue development and function, tissue development” and “cell-to-cell signaling and interaction, cell death and survival, cellular development” as the top networks. Of the two cell types, the MDA-MB-231 cells underwent a higher rate of apoptosis and a decreased proliferation rate upon plasma treatment. Taken together, these results indicate that plasma induces epigenetic and cellular changes in a cell type-specific manner, suggesting that a careful screening of target cells and tissues is necessary for the potential application of plasma as a cancer treatment option.

Secondary electron emission in a mixed gas for application to the plasma display panel

The secondary electron emission from the surface of the MgO crystal is investigated for a mixed gas in connection with applications to the plasma display panel. The experimental data indicate that the coefficient γ of the secondary emission for the neon gas mixed with a small amount of xenon is almost the same as the coefficient for the xenon-only gas. This observation agrees very well with theoretical predictions.

Influence of Penning effects on high-pressure discharge in the plasma display panel

The influence of the Penning effects on the high-pressure discharge in a neon–xenon mixed gas was investigated in connection with applications to the plasma display panel. A theoretical model of the breakdown voltage in a mixed gas is developed, based on the Townsend criteria. The breakdown temperature Tb and voltage Vb are obtained in terms of the gas mixture ratio. As an example, electrical breakdown properties in neon gas mixed with xenon are investigated. It is shown that the electron breakdown temperature Tb decreases monotonically as the xenon mole fraction χ increases. The Penning effects modify the electron temperature significantly, particularly in the range of a small mole fraction. A preliminary experiment using the plasma display panel is carried out to verify some of the theoretical models. The Paschen curves of the breakdown voltage are experimentally obtained in terms of the pressure parameter (pd) and the xenon mole fraction. It is shown that the breakdown voltage is reduced significantly ...

Self-discharge synchronizing operations in the external electrode fluorescent multi-lamps backlight

The external electrode fluorescent lamp (EEFL) is operated in a high frequency mode because the lamp lighting is basically a dielectric barrier discharge. The self-discharge synchronization is defined by synchronizing the self-discharge time of the dielectric wall charge with the voltage rising and falling time. It is shown that for the self-discharge synchronization a high brightness is obtained in the multi-lamps backlight connected in parallel with the EEFLs operated with square waves from a switching inverter. The frequency for self-discharge synchronizing is also shown to increase as the driving voltage increases.

Glow discharge in the external electrode fluorescent lamp

From the characteristics of current and voltage, the capacitive coupled external electrode fluorescent lamps are found to be similar to cold cathode fluorescent lamps having the ballast capacitors at both ends of the lamps. From the current-voltage characteristic for two types of lamps, the discharge mechanism is similar with respect to discharge process: initially a dark current, Townsend discharge with a firing voltage, followed by a normal glow. The slope and magnitude of the dark current have the same values since the gas species in the lamps are identical. At the Townsend discharge, the lamp current increases abruptly with a firing voltage of about 1 kV. In the normal glow region, the cathode fall voltage is sustained at about 600 V in the cold cathode discharge tube after Townsend breakdown at about 1 kV, while the voltage increases linearly as the current increases without negative resistance in both the external electrode lamp and the cold cathode lamp including the ballast capacitors.

Conductivity and ion density of a plasma channel induced by a mildly relativistic electron beam from a gas-filled diode

Conductivity and ion density of a plasma channel induced by a mildly relativistic electron beam (300 kV, ∼2 kA, 10–50 ns) have been experimentally investigated under various gas pressures. Pressures of filling gas (air) in this experiment ranged from 10 mTorr to 100 mTorr. The net currents of the beam-induced plasma channel were measured by four Rogowski coils located along the propagating region, while the electron beam currents were measured by a Faraday cup. The inductive plasma currents observed at the above pressure regimes have been characterized by magnetic decay time. Plasma-channel conductivity and ion density induced by the beam are measured along the propagating axial positions under various gas pressures. The numerical result of the ion density is also obtained at the charge neutralization time when the ion density is just the same as the electron beam density, and the digitizing experimental data of the beam current Ib(t) and voltage Vd(t) have been used. As expected, in both numerical and ex...

Influence of gas mixture ratio on the luminous efficiency in surface discharge alternating current plasma display panels

The improvement of luminosity and luminous efficiency is the one of the most important tasks in alternating current plasma display panels. The influence of gas mixture ratio, Ne–Xe and He–Ne(27%)–Xe(3%), on luminosity and luminous efficiency in surface discharge alternating-current plasma display panels has been investigated. It is found that discharge power does not strongly depend on the gas mixtures, while the luminosity for three species mixture gas, He–Ne(27%)–Xe(3%), is shown to be much higher than those for the two species mixture gas of Ne–Xe. The three species mixture gas, He–Ne(27%)–Xe(3%), can be suggested as the one of the candidates for achieving high luminosity and luminous efficiency for color plasma display panels, based on the experimental observations of luminosity, discharge power, response time, and efficiency.

Analytical investigation of electrical breakdown properties in a nitrogen-SF6 mixture gas

The electrical breakdown properties in nitrogen gas mixed with SF6 are analytically investigated in this article by making use of the ionization and attachment coefficients of the mixed gas. The ionization coefficients of nitrogen and SF6 gas are obtained in terms of the electron temperature Te by assuming a Maxwellian distribution of the electron energy. The attachment coefficient of SF6 gas is also obtained in terms of the gas temperature Te. An algebraic equation is obtained, relating explicitly the electron breakdown temperature Tb in terms of the SF6 mole fraction χ. It was found from this equation that the breakdown temperature Tb increases from approximately 2 to 5.3 eV as the mole fraction χ increases from zero to unity. The breakdown temperature Tb of the electrons increases very rapidly from a small value and then approaches 5.3 eV slowly as the SF6 mole fraction increases from zero to unity. This indicates that even a small mole fraction of SF6 in the gas dominates the electron behavior in the ...