Hea Min Joh

Optical and electrical characterization of an atmospheric pressure microplasma jet with a capillary electrode

A microplasma jet with a capillary electrode working at atmospheric pressure is developed to create nonthermal plasma. This jet can be operated at an excitation frequency either in several tens of kilohertz ac range (or pulsed voltage with a repetition rate of kilohertz range) or in radio-frequency range. The working gas, helium or argon, and the additive gas, oxygen, are fed into the plasma jet. The discharge has been characterized by optical emission spectroscopy. The electrical property of the discharge has been studied by means of voltage and current probes. The dynamic nature of the plume is investigated by using intensified charged coupled device camera. The electron temperature is estimated from the modified Boltzmann plot method utilizing the Ar 4p→4s transitions. The plume temperature is determined by using the fitting the fine structure of the emission bands of OH molecules and by utilizing the line shape of the transition. They are compared with the results obtained by optical fiber thermometer...

Effect of additive oxygen gas on cellular response of lung cancer cells induced by atmospheric pressure helium plasma jet

The atmospheric pressure helium plasma jet driven by pulsed dc voltage was utilized to treat human lung cancer cells in vitro. The properties of plasma plume were adjusted by the injection type and flow rate of additive oxygen gas in atmospheric pressure helium plasma jet. The plasma characteristics such as plume length, electric current and optical emission spectra (OES) were measured at different flow rates of additive oxygen to helium. The plasma plume length and total current decreased with an increase in the additive oxygen flow rate. The electron excitation temperature estimated by the Boltzmann plot from several excited helium emission lines increased slightly with the additive oxygen flow. The oxygen atom density in the gas phase estimated by actinometry utilizing argon was observed to increase with the additive oxygen flow. The concentration of intracellular reactive oxygen species (ROS) measured by fluorescence assay was found to be not exactly proportional to that of extracellular ROS (measured by OES), but both correlated considerably. It was also observed that the expression levels of p53 and the phospho-p53 were enhanced in the presence of additive oxygen flow compared with those from the pure helium plasma treatment.

Comparison of the characteristics of atmospheric pressure plasma jets using different working gases and applications to plasma-cancer cell interactions

Atmospheric pressure plasma jets employing nitrogen, helium, or argon gases driven by low-frequency (several tens of kilohertz) ac voltage and pulsed dc voltage were fabricated and characterized. The changes in discharge current, optical emission intensities from reactive radicals, gas temperature, and plume length of plasma jets with the control parameters were measured and compared. The control parameters include applied voltage, working gas, and gas flow rate. As an application to plasma-cancer cell interactions, the effects of atmospheric pressure plasma jet on the morphology and intracellular reactive oxygen species (ROS) level of human lung adenocarcinoma cell (A549) and human bladder cancer cell (EJ) were explored. The experimental results show that the plasma can effectively control the intracellular concentrations of ROS. Although there exist slight differences in the production of ROS, helium, argon, or nitrogen plasma jets are found to be useful in enhancing the intracellular ROS concentrations in cancer cells.

Non-thermal plasma-induced apoptosis is modulated by ATR- and PARP1-mediated DNA damage responses and circadian clock

Non-thermal plasma (NTP) has been emerging as a potential cancer therapeutic. However, the practical use of NTP as a cancer therapy requires a better understanding of the precise mechanisms underlying NTP-induced DNA damage responses in order to achieve optimal efficacy. It has been shown that the addition of oxygen gas flow during NTP treatment (NTPO), when compared to NTP exposure alone, can induce a 2–3 fold greater generation of intracellular reactive oxygen species (ROS) in A549 cells. Here, we examined NTPO-induced DNA damage responses and found that NTPO generated a substantial number of genomic DNA lesions and breaks that activated ATR-mediated cell-cycle checkpoints. In addition, we discovered that NTPO-induced DNA lesions were primarily removed by base excision repair (BER) rather than by nucleotide excision repair (NER). Therefore, the inhibition of the BER pathway using a PARP1 inhibitor drastically induced the phosphorylation of γH2AX, and was followed by the programmed cell death of cancer cells. However, the knock-down of XPA, which inhibited the NER pathway, had no effect on NTPO-induced phosphorylation of γH2AX. Finally, in agreement with a recent report, we found a circadian rhythm of PARP1 activity in normal mouse embryonic fibroblasts that needed for cell viability upon NTPO treatment. Taken together, our findings provided an advanced NTP regimen for cancer treatment by combining NTPO treatment with chemical adjuvants for the inhibition of ATR- and PARP1-activated DNA damage responses, and circadian timing of treatment.

Characteristics of Multiple Plasma Plumes and Formation of Bullets in an Atmospheric- Pressure Plasma Jet Array

An atmospheric-pressure plasma jet array source driven by a pulsed bipolar wave of several tens of kilohertz was designed and characterized. This source was assembled with each individual module. Thus, it is possible to adjust the area of treatment by arranging the number of jets. It has the potential to greatly enhance the scale of surface treatment over that of a single plasma jet. Multiple plasma plumes were generated and propagated to grounded-surface relatively uniformly without an auxiliary circuit. Due to the large separation between each jet, plasma bullets propagate through their individual gas channels. The transition from the bullet to the continuous modes occurred at an applied voltage of 5.5 kVpp. The interaction between adjacent plasma plumes and behaviors of primary bullet and subbullet are investigated with intensified charge coupled device camera images.

Pressure dependence of dissociation fraction and optical emission characteristics in low-pressure inductively coupled N2-Ar plasmas

A diagnostics study of low-pressure inductively coupled N2-Ar plasmas was performed by using optical emission spectroscopy (OES) and an rf-compensated Langmuir probe under the conditions of pressures of 1 - 30 mTorr and powers of 300 - 600 W. In the OES experiments, the argon was used as an actinometer and as an adding gas. The effect of the argon content in the gas mixture was examined in the range of 5 - 30%. The investigation of the effects of pressure on the dissociation fraction of nitrogen molecules and on the optical emission characteristics were carried out. The correction factors for estimating the dissociation fraction by OES actinometry accounting for argon effect were formulated and calculated. It was found that the dissociation fraction increased with increasing power and Ar content, while it decreased with increasing pressure. In addition, the electron energy probability function (EEPF), the electron density, and the electron temperature were obtained by using a Langmuir probe to investigate...

Effects of the electrical parameters and gas flow rate on the generation of reactive species in liquids exposed to atmospheric pressure plasma jets

In this work, an atmospheric pressure plasma jet was fabricated and studied for plasma–liquid interactions. The plasma jet consists of a quartz-covered pin electrode and outer quartz tube with a tapered nozzle. Using the current–voltage (I-V) and optical emission characteristics of the plasma jet, the plasma density and the speed of the plume were investigated. The optical emission spectra clearly indicated the excited NO, O, OH, N2, and N2+ in the plasma plumes. Then the plasma jets were applied to the deionized water. We investigated the effects of the operating parameters such as applied voltage, pulse frequency, and gas flow rate on the generation of reactive species in the gas and liquid phases. The densities of reactive species including OH radicals were obtained at the plasma–liquid surface and inside the plasma-treated liquids using ultraviolet absorption spectroscopy and chemical probe method. The nitrite concentration was detected by Griess assay. The data are very suggestive that there is a str...

Electrical and Optical Characterization of Atmospheric-Pressure Helium Plasma Jets Generated With a Pin Electrode: Effects of the Electrode Material, Ground Ring Electrode, and Nozzle Shape

This paper tests various design and operation parameters in atmospheric-pressure helium plasma jets generated with a pin electrode to provide a plasma environment well suited for material processing or biomedical applications. The effects of the pin electrode materials (Cu, W, and Al), the position, and the width of a ground ring electrode on the characteristics of the jets are studied. The inner quartz tube encompassing the pin electrode and two types of the outer quartz tubes (straight or tapered cylinder shape) are employed, and their effects are investigated. The electrical characteristics of the plasma jets are measured by current-voltage measurements and analyzed by the equivalent circuit model. The optical characteristics of the discharges are obtained by optical emission spectroscopy to identify various excited plasma species produced in the plasma jets. Optical emission spectra are also obtained at different positions along the coaxial direction. A variety of choices in design parameters and operation parameters are undertaken to determine optimal conditions and elucidate the properties of the plasma jets.

Effects of Dielectric Tube Shape and Pin-Electrode Diameter on the Plasma Plume in Atmospheric Pressure Helium Plasma Jets

This paper explores the effects of tube shape and pin electrode diameter on the plume generation and electrical characteristics in atmospheric pressure helium plasma jets generated from a centered-pin electrode inside a dielectric tube. The quartz-covered (or bare) pin electrode and different shapes of the dielectric tube (straight cylinder or conical shape) are employed and their effects are investigated. Optical emission spectra are obtained at different positions along the coaxial direction to determine the axial distributions of the electron excitation temperature for the straight cylinder and conical jets. The rotational temperatures for the both jets are also compared.

Effects of the pulse width on the reactive species production and DNA damage in cancer cells exposed to atmospheric pressure microsecond-pulsed helium plasma jets

Plasma-liquid and plasma-cell interactions were investigated using an atmospheric pressure dc microsecond-pulsed helium plasma jet. We investigated the effects of the electrical parameters such as applied voltage and pulse width (determined by the pulse frequency and duty ratio) on the production of reactive species in the gas/liquid phases and on the DNA damage responses in the cancer cells. The densities of reactive species including OH radicals were estimated inside the plasma-treated liquids using a chemical probe method, and the nitrite concentration was detected by Griess assay. Importantly, the more concentration of OH resulted in the more DNA base oxidation and breaks in human lung cancer A549 cells. The data are very suggestive that there is strong correlation between the production of OH in the plasmas/liquids and the DNA damage.