Han Sup Uhm

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.

Work function of MgO single crystals from ion-induced secondary electron emission coefficient

The work functions φω of MgO single crystals with its respective orientation (111), (200), and (220) have been investigated from their ion-induced secondary electron emission coefficient γ, respectively, using various ions with different ionization energies in a γ-focused ion beam system. The work function φω for MgO single crystal with (111) orientation has the lowest value, 4.22 eV, whereas it is 4.94 eV for (200) and the highest value is 5.07 eV for (220). These work functions of MgO single crystals can explain the nonzero values of the ion-induced secondary electron emission coefficient γ for Xe+ ions, whose ionization energy is 12.13 eV.

Atmospheric pressure air-plasma jet evolved from microdischarges: Eradication of E. coli with the jet

An atmospheric-pressure air-plasma jet operating at 60 Hz ac is presented. A plasma jet with a length of 23 mm was produced by feeding air through a porous alumina dielectric installed between an outer electrode and a hollow inner electrode. Microdischarges in the porous alumina are ejected as a plasma jet from the outer electrode through a 1 mm hole, showing that the temperature of the jet decreases to a value close to the room temperature. The jet disinfects E. coli cells very effectively, eradicating them with an exposure of a few seconds to the jet flame.

Air plasma jet with hollow electrodes at atmospheric pressure

Atmospheric-pressure plasma jet with air is produced through hollow electrodes and dielectric with a hole of 1mm diam. The plasma jet device is operated by injecting pressurized air into the electrode hole. The air plasma jet device at average powers less than 5W exhibits a cold plasma jet of about 2cm in length and near the room temperature, being low enough to treat thermally sensitive materials. Preliminary studies on the discharge characteristics and application tests are also presented by comparing the air plasma jet with the nitrogen and argon plasma jet.

Atmospheric pressure nitrogen plasma jet: Observation of striated multilayer discharge patterns

This paper presents a nitrogen microplasma jet that operates at atmospheric pressure and provides details of an observation of the striated multilayer discharge patterns formed in the plasma jet. The plasma jet device in a microhollow electrode is a pencil-type configuration that produces a long cold plasma jet capable of reaching 3.5cm and having various excited plasma species shown through optical emission spectrum. By introducing a gas flow rate of more than 5l∕min, striated discharge patterns in the plasma jet are produced through ionization wave propagation.

Plasma formation using a capillary discharge in water and its application to the sterilization of E. coli

An underwater electrical discharge in a narrow dielectric capillary provides the details of the evolution of microbubbles to plasma as formed by a tungsten electrode inserted in the capillary. An increase in the applied voltage forms microbubbles after water fills the capillary. A further increase in the voltage generates a surface discharge through the boundary of the bubble, elongating the bubble shape, and eventually forming plasma by electrical breakdown. This produces atomic oxygen, atomic hydrogen, and hydroxyl radicals from dissociation of water vapor. Also, a bactericidal test in normal saline solution showed that more than 99.6% of the bacterial cells were killed within 8 s, resulting from chlorine-containing species, in particular hypochlorous acid as a major bactericidal agent.

Induced apoptosis in melanocytes cancer cell and oxidation in biomolecules through deuterium oxide generated from atmospheric pressure non-thermal plasma jet

Recently, atmospheric-pressure non-thermal plasma-jets (APPJ) are being for the cancer treatment. However, APPJ still has drawbacks such as efficiency and rise in temperature after treatment. So, in this work, a synergetic agent D2O vapour is attached to APPJ which not only increase the efficiency of plasma source against cancer treatment, but also controlled the temperature during the treatment. OD generated by the combination of D2O + N2 plasma helped in enhancing the efficiency of APPJ. We observed OD induced apoptosis on melanocytes G361 cancer cells through DNA damage signalling cascade. Additionally, we observed that plasma induces ROS, which activated MAPK p38 and inhibits p42/p44 MAPK, leading to cancer cell death. We have also studied DNA oxidation by extracting DNA from treated cancer cell and then analysed the effects of OD/OH/D2O2/H2O2 on protein modification and oxidation. Additionally, we attempted molecular docking approaches to check the action of D2O2 on the apoptosis related genes. Further, we confirmed the formation of OD/OH simultaneously in the solution using optical emission spectroscopy. Moreover, the simultaneous generation of D2O2/H2O2 was detected by the use of confocal Raman spectroscopy and density measurements.

Hydrophobic coating of carbon nanotubes by CH4 glow plasma at low pressure, and their resulting wettability

This study demonstrates the hydrophobic coating of carbon nanotubes (CNTs) by methane (CH4) glow discharge plasma at low pressure and investigates the superhydrophobic behavior of the treated CNTs. Carbonaceous species produced from the CH4 glow plasma were identified by optical emission spectroscopy. The treated CNTs floated on water for several months, exhibiting hydrophobic properties. Contact angles (CAs) with test liquids were measured from the capillary rise method based on the Washburn equation, to identify the total surface free energies of CNTs with and without CH4 plasma treatment. The total surface free energy of the CNTs can be determined by making use of the measured CA and the van Oss–Chaudhury–Good equation. It was shown that the surface free energy of the plasma-treated CNTs decreased drastically from 27.04 mN m−1 to 1.32 × 10−7 mN m−1, revealing super-hydrophobic modification of CNTs by the CH4 plasma.

Cold Plasma Jets Made of a Syringe Needle Covered With a Glass Tube

A syringe needle assembled with a glass tube has been used as a plasma jet device for biomedical applications. According to the various types of ground electrode installed at the glass tube, argon plasma from an atmospheric pressure discharge has been investigated with a dc-ac inverter of several tens of kilohertz. When the ground electrode is absent or floated, the length of the plasma jet is about 10 mm at an ignition voltage of about 3 kV, and it extends further to a few tens of millimeters as the voltage increases to 5 kV. If the ground electrode is inserted inside the end of the glass tube, all plasma current is sunk directly to the ground electrode so that the plasma plume cannot emit out of the glass tube. For the case of an external ground electrode which is similar to a dielectric barrier discharge, the ignition voltage is as low as 1 kV, and the plume length is easily adjustable to be 1-10 mm in the voltage range of 1-3 kV.

Microwave plasma burner and temperature measurements in its flames

An apparatus for generating flames and more particularly the microwave plasma burner for generating high-temperature large-volume plasma flame was presented. The plasma burner is operated by injecting liquid hydrocarbon fuels into a microwave plasma torch in air discharge and by mixing the resultant gaseous hydrogen and carbon compounds with air or oxygen gas. The microwave plasma torch can instantaneously vaporize and decompose the hydrogen and carbon containing fuels. It was observed that the flame volume of the burner was more than 50 times that of the torch plasma. While the temperature of the torch plasma flame was only 550K at a measurement point, that of the plasma-burner flame with the addition of 0.025lpm (liters per minute) kerosene and 20lpm oxygen drastically increased to about 1850K. A preliminary experiment was carried out, measuring the temperature profiles of flames along the radial and axial directions.