Young June Hong

Generation mechanism of hydroxyl radical species and its lifetime prediction during the plasma-initiated ultraviolet (UV) photolysis

Through this work, we have elucidated the mechanism of hydroxyl radicals (OH•) generation and its life time measurements in biosolution. We observed that plasma-initiated ultraviolet (UV) photolysis were responsible for the continues generation of OH• species, that resulted in OH• to be major reactive species (RS) in the solution. The density and lifetime of OH• species acted inversely proportional to each other with increasing depth inside the solution. The cause of increased lifetime of OH• inside the solution is predicted using theoretical and semiempirical calculations. Further, to predict the mechanism of conversion of hydroxide ion (OH−) to OH• or H2O2 (hydrogen peroxide) and electron, we determined the current inside the solution of different pH. Additionally, we have investigated the critical criterion for OH• interaction on cancer cell inducing apoptosis under effective OH• exposure time. These studies are innovative in the field of plasma chemistry and medicine.

Responses of Solid Tumor Cells in DMEM to Reactive Oxygen Species Generated by Non-Thermal Plasma and Chemically Induced ROS Systems

In this study, we assessed the role of different reactive oxygen species (ROS) generated by soft jet plasma and chemical-induced ROS systems with regard to cell death in T98G, A549, HEK293 and MRC5 cell lines. For a comparison with plasma, we generated superoxide anion (O2−), hydroxyl radical (HO·), and hydrogen peroxide (H2O2) with chemicals inside an in vitro cell culture. Our data revealed that plasma decreased the viability and intracellular ATP values of cells and increased the apoptotic population via a caspase activation mechanism. Plasma altered the mitochondrial membrane potential and eventually up-regulated the mRNA expression levels of BAX, BAK1 and H2AX gene but simultaneously down-regulated the levels of Bcl-2 in solid tumor cells. Moreover, a western blot analysis confirmed that plasma also altered phosphorylated ERK1/2/MAPK protein levels. At the same time, using ROS scavengers with plasma, we observed that scavengers of HO· (mannitol) and H2O2 (catalase and sodium pyruvate) attenuated the activity of plasma on cells to a large extent. In contrast, radicals generated by specific chemical systems enhanced cell death drastically in cancer as well as normal cell lines in a dose-dependent fashion but not specific with regard to the cell type as compared to plasma.

Cellular and molecular responses of Neurospora crassa to non-thermal plasma at atmospheric pressure

Filamentous fungi have been rarely explored in terms of plasma treatments. This letter presents the cellular and molecular responses of the filamentous fungus Neurospora crassa to an argon plasma jet at atmospheric pressure. The viability and cell morphology of N. crassa spores exposed to plasma were both significantly reduced depending on the exposure time when treated in water. The intracellular genomic DNA content was dramatically reduced in fungal tissues after a plasma treatment and the transcription factor tah-3 was found to be required for fungal tolerance to a harsh plasma environment.

Measurement of hydroxyl radical density generated from the atmospheric pressure bioplasma jet

Atmospheric pressure bioplasmas are being used in a variety of bio-medical and material processing applications, surface modifications of polymers. This plasma can generate the various kinds of radicals when it contacs with the water. Especially, hydroxyl radical species have very important role in the biological and chemical decontamination of media in this situation. It is very important to investigate the hydroxyl radical density in needle-typed plasma jet since it plays a crucial role in interaction between the living body and plasma. We have generated the needle-typed plasma jet bombarding the water surface by using an Ar gas flow and investigated the emission lines by OES (optical emission spectroscopy). It is noted that the electron temperature and plasma density are measured to be about 1.7 eV and 3.4 × 1012 cm−3, respectively, under Ar gas flow ranged from 80 to 300 sccm (standard cubic centimeter per minute) in this experiment. The hydroxyl radical density has also been investigated and measured to be maximum value of 2.6 × 1015 cm−3 for the gas flow rate of 150 sccm in the needle-typed plasma jet by the ultraviolet optical absorption spectroscopy.

Cytotoxic macrophage-released tumour necrosis factor-alpha (TNF-α) as a killing mechanism for cancer cell death after cold plasma activation

The present study aims at studying the anticancer role of cold plasma-activated immune cells. The direct anti-cancer activity of plasma-activated immune cells against human solid cancers has not been described so far. Hence, we assessed the effect of plasma-treated RAW264.7 macrophages on cancer cell growth after co-culture. In particular, flow cytometer analysis revealed that plasma did not induce any cell death in RAW264.7 macrophages. Interestingly, immunofluorescence and western blot analysis confirmed that TNF-α released from plasma-activated macrophages acts as a tumour cell death inducer. In support of these findings, activated macrophages down-regulated the cell growth in solid cancer cell lines and induced cell death in vitro. Together our findings suggest plasma-induced reactive species recruit cytotoxic macrophages to release TNF-α, which blocks cancer cell growth and can have the potential to contribute to reducing tumour growth in vivo in the near future.

Analysis of the antimicrobial effects of nonthermal plasma on fungal spores in ionic solutions

The antimicrobial efficiency of reactive species-based control strategies is significantly affected by the dynamics of reactive species in the biological environment. Atmospheric-pressure nonthermal plasma is an ionized gas in which various reactive species are produced. The various levels of antimicrobial activity may result from the dynamic interaction of the plasma-generated reactive species with the environment. However, the nature of the interaction between plasma and environments is poorly understood. In this study, we analyzed the influence of the ionic strength of surrounding solutions (environment) on the antimicrobial activity of plasma in relation to the plasma-generated reactive species using a model filamentous fungus, Neurospora crassa. Our data revealed that the presence of sodium chloride (NaCl) in the background solution attenuated the deleterious effects of plasma on germination, internal structure, and genomic DNA of fungal spores. The protective effects of NaCl were not explained exclusively by pH, osmotic stability, or the level of reactive species in the solution. These were strongly associated with the ionic strength of the background solution. The presence of ions reduced plasma toxicity, which might be due to a reduced access of reactive species to fungal spores, and fungal spores were inactivated by plasma in a background fluid of nonionic osmolytes despite the low level of reactive species. Our results suggest that the surrounding environment may affect the behavior of reactive species, which leads to different biological consequences regardless of their quantity. Moreover, the microbicidal effect of plasma can be synergistically regulated through control of the microenvironment.

Measurement of Electron Temperature and Density Using Stark Broadening of the Coaxial Focused Plasma for Extreme Ultraviolet Lithography

We have generated an Ar plasma in a dense plasma focus device with coaxial electrodes for extreme ultraviolet (EUV) lithography and investigated an emitted visible light for electrooptical plasma diagnostics. We have applied an input voltage of 4.5 kV to the capacitor bank of 1.53 ¿F, and the diode chamber has been filled with Ar gas of 8-mtorr pressure. The inner surface of the cylindrical cathode has been attached by an acetal insulator. Also, the anode is made of tin metal. If we assumed that the focused plasma regions satisfy the local thermodynamic equilibrium conditions, the electron temperature and density of the coaxial plasma focus could be obtained by the Stark broadening of optical emission spectroscopy. The Lorentzian profile for the emission lines of Ar I of 426.629 nm and Ar II of 487.99 nm were measured with a visible monochromator. In addition, the electron density has been estimated by the full-width at half-maximum (FWHM) of its profile. To find the exact value of FWHM, we observed the instrumental line broadening of the monochromator with a Hg-Ar reference lamp. The electron temperature has been calculated using the two relative electron-density ratios of the Stark profiles. In case of electron density, it has been observed by the Stark broadening method. This experimental result shows the temporal behavior of the electron temperature and density characteristics for the focused plasma. The EUV emission signal whose wavelength is about 6-16 nm has been detected by using a photodetector (AXUV-100 Zr/C, IRD). The result compared the electron temperature and density with the temporal EUV signal. The electron density and temperature were observed to be 1016 cm-3 and 20-30 eV, respectively.

The effect of the gap distance between an atmospheric-pressure plasma jet nozzle and liquid surface on OH and N2 species concentrations

An argon plasma jet at atmospheric pressure was operated at various gap distances between the nozzle of the plasma jet and the water surface in order to study the formation of OH and N2 species in the vicinity of the water surface. Plasma was generated using a 24 kHz sinusoidal power supply at a steady gas flow-rate of 200 sccm. The electron temperature and rotational temperature of gas species were measured using optical emission spectroscopy and found to decrease with increasing gap distance. Meanwhile, the electron density calculated from jet current measurement increased with increasing gap distance. The average OH concentration reduced from 6.10 × 1015 cm−3 to 1.35 × 1015 cm−3, as the gap distance increased from 1 to 4 mm. The 337 nm N2 second positive system studied by optical emission spectroscopy and temporal emission signals increased with increasing gap distance. Plasma activated water was also made from various gap distances in order to confirm the presence of particular reactive oxygen or nitr...

Measurement of the valence band structure in dielectric films by a focused ion beam

The measured profile of the energy distribution of electrons emitted from dielectric films due to the Auger neutralization of incoming ions is rescaled to facilitate the Auger self-convolution, which illustrates the details of the valence band. As an application for this research scheme, the properties of the valence band in MgO layers are investigated in terms of the measured Auger self-convolution, indicating that the state density is a decaying function of the energy deviation from the band of e0=7.63 eV, although a numerical calculation shows a spiky structure of the state density in the valence band.

A Novel Approach to Inactivate the Clinical Isolates of Trichophytonmentagrophytes and Trichophyton rubrum by Using Non-Thermal Plasma

In this study, we propose a novel approach that uses non-thermal plasma to inactivate dermatophytes, and we evaluate the antifungal activity of the proposed method using an In vitro infected skin model with clinical isolates of dermatophytes. For this study, a floating electrode-dielectric barrier discharge (FE-DBD) plasma jet was the source for non-thermal plasma, and we investigated its antifungal activity on Trichophyton mentagrophytes (T. mentagrophytes) and Trichophyton rubrum (T. rubrum), two clinical isolates of dermatophytes. These two strains are the most frequently isolated from skin, hair, and nail infections for use in an infected skin model. The results of this study confirm that the FE-DBD plasma jet has statistically significant antifungal activity in saline and in an infected skin model, and after plasma treatment; we also observed a significant inhibition of the growth of the conidia and hypha for both strains in the infected skin mimicking model. In addition, we found a time-dependent correlation between the intracellular reactive species and the fungal cell viabilities after exposure to plasma. These results indicate FE-DBD plasma can inactivate clinically isolated dermatophyte species and suggest that non-thermal plasma may be an effective tool for use in supportive and/or alternative treatments for dermatophytosis.