Microwave-excited Atmospheric Pressure Plasma Research Articles

Plasma-Activated Media Produced by a Microwave-Excited Atmospheric Pressure Plasma Jet Is Effective against Cisplatin-Resistant Human Bladder Cancer Cells In Vitro.

Media exposed to atmospheric pressure plasma (APP) produce reactive oxygen and nitrogen species (RONS), with hydrogen peroxide (H2O2), nitrite (NO2-), and nitrate (NO3-) being among the most detected species due to their relatively long lifetime. In this study, a standardized microwave-excited (ME) APP jet (APPJ) source was employed to produce gaseous RONS to treat liquid samples. The source was a commercially available plasma jet, which generated argon plasma utilizing a coaxial transmission line resonator at the operating frequency of 2.45 GHz. An ultraviolet-visible spectrophotometer was used to measure the concentrations of H2O2 and NO3- in plasma-activated media (PAM). Three different types of media (deionized water, Hank's balanced salt solution, and cell culture solution Dulbecco's modified eagles medium [DMEM]) were utilized as liquid samples. Among these media, the plasma-treated DMEM was observed to have the highest levels of H2O2 and NO3-. Subsequently, the feasibility of using argon ME-APPJ-activated DMEM (PAM) as an adjuvant to enhance the therapeutic effects of cisplatin on human bladder cancer cells (T-24) was investigated. Various cancer cell lines, including T-24 cells, treated with PAM were observed in vitro for changes in cell viability using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. A viability reduction was detected in the various cancer cells after incubation in PAM. Furthermore, the study's results revealed that PAM was effective against cisplatin-resistant T-24 cells in vitro. In addition, a possible connection between HER expression and cell viability was sketched.

Dual microwave-excited atmospheric-pressure plasma jets with a single power source

In this paper, we propose dual microwave-excited atmospheric-pressure plasma jets (DME-APPJs) that can be generated with a single power source. A T-junction power divider that evenly distributes the input power to two ports is used, and two coaxial transmission line resonators are used as plasma generators for the DME-APPJs. The power divider distributes the incoming power in port 1 and supplies 46% of this power to port 2 and port 3, respectively. Surface treatments are conducted by exposing the multiple plasma jets to polypropylene (PP) specimens and then confirming the degree of hydrophilic change. Using the proposed DME-APPJs, it is possible to perform surface treatments on areas that are up to 50% larger compared to using two single ME-APPJs with the same power consumption. The DME-APPJs thus show more advanced performance for surface treatments by comparison with the single ME-APPJ.

Plasma Diagnosis and Biomedical Application Using Linear Microwave Atmospheric- Pressure Plasma Generator

A new type of microwave-excited atmospheric-pressure plasma (APP) generator that uses the principle of a strip-line transmission line resonator is presented. The microwave plasma has a length of 30 mm, so it can treat a wide area at the same time. The impedance of the resonator was matched to $50~\Omega $ without additional matching equipment by exploiting characteristic of quarter wavelength transmission line. The design of the resonator was double-checked by computer simulation for the purpose of generating stable microwave APP. Microwave plasma discharge of the resonator was operated with argon gas flow of 1 slm, net power of 2.3 W, and resonance frequency of 2.41 GHz. The plasma gas temperature was maintained below 40 °C for 30 min, so it is safe to use in biomedical applications. The intensity of optical emission spectrum was higher at the center than edges. The average of electron excitation temperature was 0.78 eV with a standard deviation of 0.03 eV (3.85%) in 20-mm range. Increase in the amount of reactive oxygen and nitrogen species expressed in the normal human dermal fibroblast cells after plasma treatment was confirmed using fluorescent reagent. This new type of microwave atmospheric plasma resonator is expected to be useful in various biomedical fields.

Anticancer Effects of Plasma-Activated Medium Produced by a Microwave-Excited Atmospheric Pressure Argon Plasma Jet.

Cold atmospheric plasma (CAP) has been reported to have strong anticancer effects in vitro and in vivo. CAP has been known to induce apoptosis in most cancer cells by treatment to cells using direct and indirect treatment methods. There are many reports of apoptosis pathways induced by CAP, but for indirect treatment, there is still a lack of fundamental research on how CAP can cause apoptosis in cancer cells. In this study, we applied an indirect treatment method to determine how CAP can induce cancer cell death. First, plasma-activated medium (PAM) was produced by a 2.45 GHz microwave-excited atmospheric pressure plasma jet (ME-APPJ). Next, the amounts of various reactive species in the PAM were estimated using colorimetric methods. The concentration of NO2– and H2O2 in PAM cultured with cancer cells was measured, and intracellular reactive oxidative stress (ROS) changes were observed using flow cytometry. When PAM was incubated with A549 lung cancer cells, there was little change in NO2– concentration, but the concentration of H2O2 gradually decreased after 30 min. While the intracellular ROS of A549 cells was rapidly increased at 2 hours, there was no significant change in that of PAM-treated normal cells. Furthermore, PAM had a significant cytotoxic effect on A549 cells but had little effect on normal cell viability. In addition, using flow cytometry, we confirmed that apoptosis of A549 cells occurred following flow cytometry and western blot analysis. These results suggest that among various reactive species produced by PAM, hydrogen peroxide plays a key role in inducing cancer cell apoptosis.

Cell viability and measurement of reactive species in gas- and liquid-phase exposed by a microwave-excited atmospheric pressure argon plasma jet

Abstract A microwave-excited atmospheric pressure plasma jet (ME-APPJ) was generated utilizing coaxial transmission line resonators with the resonance frequency of 788 MHz. We investigated the effects of the operating parameters such as input power and gas flow rate on the electron excitation temperature and electron density using optical emission spectroscopy. The amounts of various reactive species in the plasma-activated media (PAM) exposed by the ME-APPJ were estimated using colorimetric methods. The PAM was applied to A549 cultured cells and subsequently incubated for a given duration. The concentrations of NO2− and H2O2 in the PAM incubating A549 cells were monitored until 24 h. The reduced cell viability rate was observed on A549 cells incubated in the PAM. The concentrations of NO2− and H2O2 and the viability of A549 cells depended on the operating conditions of ME-APPJ. The cell viability rate exhibited a decrease with increasing power and decreasing gas flow rate. Correlation between the concentrations of gaseous reactive species in the plasma and in the PAM and the cell viability is discussed.

Thin film deposition method for ZnO nanosheets using low-temperature microwave-excited atmospheric pressure plasma jet

Abstract Electronic devices such as solar cells and thin-film transistors can be fabricated using thin-film deposition. Low-cost, low-temperature and high-speed deposition methods are required to ensure that the production of devices using thin-film deposition is affordable. Herein, we report the development of a low-cost and simple thin-film deposition method using microwave-excited atmospheric pressure plasma jet (MWAPPJ). MWAPPJ produces a low-temperature (several hundred degrees) plasma under atmospheric conditions, does not require expensive vacuum equipment, and it enables high-speed deposition of thin-films. Zinc acetylacetonate sol-gel precursors that were adhered to stainless steel mesh targets were irradiated by MWAPPJ with oxygen, which resulted in zinc oxide (ZnO) nanosheet thin-films with diameters of 100–200 nm on silicon substrates. We used 50-nm-thick ZnO thin-films that were processed using MWAPPJ as the electron collection layer in organic photovoltaic (OPV) cells. This work represents an important contribution to the design and production of low-cost OPV solar cells.

Characterization of a microwave-excited atmospheric-pressure argon plasma jet using two-parallel-wires transmission line resonator

This paper presents a method to produce a microwave-excited atmospheric-pressure plasma jet (ME-APPJ) with argon. The plasma was generated by a microwave-driven micro-plasma source that uses a two-parallel-wire transmission line resonator (TPWR) operating at around 900 MHz. The TPWR has a simple structure and is easier to fabricate than coaxial transmission line resonator (CTLR) devices. In particular, the TPWR can sustain more stable ME-APPJ than the CTLR can because the gap between the electrodes is narrower than that in the CTLR. In experiments performed with an Ar flow rate from 0.5 to 8.0 L·min−1 and an input power from 1 to 6 W, the rotational temperature was determined by comparing the measured and simulated spectra of rotational lines of the OH band and the electron excitation temperature determined by the Boltzmann plot method. The rotational temperature obtained from OH(A-X) spectra was 700 K to 800 K, whereas the apparent gas temperature of the plasma jet remains lower than ∼325 K, which is compatible with biomedical applications. The electron number density was determined using the method based on the Stark broadening of the hydrogen Hβ line, and the measured electron density ranged from 6.5 × 1014 to 7.6 × 1014 cm−3. TPWR ME-APPJ can be operated at low flows of the working gas and at low power and is very stable and effective for interactions of the plasma with cells.

Optical emission and surface characterization of stainless steel treated by pulsed microwave-atmospheric helium plasma jet

A pulsed microwave-excited atmospheric pressure plasma jet MWAPPJ in helium, has been investigated by optical emission spectroscopy OES. Beside helium spectral lines various excited species such as atomic oxygen OI, hydrogen H α line, N2 + ion and nitrogen molecule species N2 (C3Πu) which are responsible for metal surface activation. The rotational T rot and vibrational temperature T vib were evaluated using optical emission spectroscopy and their dependences on the pulsed microwave parameters such as duty factor (20–70%) and a repetition rate (4 to 90 kHz) are investigated. Spectroscopic measurements show that, T rot, T vib and relative emission intensity of excited species greatly increases with increasing pulse duty factor. Meanwhile they show weak dependences as repetition frequency increased. Surface characterization of the examined stainless steel samples were performed through contact angle, Atomic force microscope AFM and X-ray photoelectron emission spectroscopy XPS. The contact angle decreased from 71° to 20° after pulsed MWAPPJ helium plasma at duty factor of 70% treatment for 30 s, which it is mainly due to incorporation of oxygen-containing functional groups as inferred from XPS results.

Plasma assisted lubrication by microwave-excited atmospheric pressure plasma jet using microstrip line

Plasma assisted lubrication by microwave-excited atmospheric pressure plasma jet using microstrip line

Microwave-excited atmospheric pressure plasma jet with wide aperture for the synthesis of carbon nanomaterials

Atmospheric pressure chemical vapor deposition (APCVD) has preferable properties to the mass production of carbon nanomaterials. Here, we describe a specially-designed microwave-excited atmospheric pressure plasma jet (MW-APPJ) with a 10-mm-wide nozzle based on microstrip line. The MW-APPJ is applied to an APCVD process and nanocrystalline diamond films are successfully deposited on silicon substrates using a mixture gas of Ar/CH4/H2 even in ambient air. The MW-APPJ technology could be suitable for the large-area APCVD system for the synthesis of carbon nanomaterials due to its arrayed configuration for the enlargement of plasma area.

Synergistic sterilization effect of microwave-excited nonthermal Ar plasma, H2O2, H2O and TiO2, and a global modeling of the interactions

A microwave-excited atmospheric-pressure plasma jet (uAPPJ) exhibited a synergistic sterilization effect when combined with hydrogen peroxide (H2O2), distilled water (DW) and titanium dioxide (TiO2) photocatalysis. The sterilization efficacy of H2O2–uAPPJ increased as the H2O2 concentration increased. The addition of TiO2 also remarkably increased the sterilization efficacy. To find the main factor for the sterilization effect, optical emission spectra and the degradation rate of a methylene blue solution were measured. Numerical analysis, a newly developed global modeling, was also conducted to discover the mechanisms. Both experimental measurements and global modeling results suggested that combinations of H2O2, DW and TiO2 increased the generation of hydroxyl radicals (·OH), which are known to be strong bactericidal agents. It was revealed that charged species, especially electrons, have a dominant role in the increase of ·OH.

Slit shaped microwave induced atmospheric pressure plasma based on a parallel plate transmission line resonator

A new type of microwave-excited atmospheric pressure plasma source, based on the principle of parallel plate transmission line resonator, is developed for the treatment of large areas in biomedical applications such as skin treatment and wound healing. A stable plasma of 20 mm width is sustained by a small microwave power source operated at a frequency of 700 MHz and a gas flow rate of 0.9 slm. Plasma impedance and plasma density of this plasma source are estimated by fitting the calculated reflection coefficient to the measured one. The estimated plasma impedance shows a decreasing trend while estimated plasma density shows an increasing trend with the increase in the input power. Plasma uniformity is confirmed by temperature and optical emission distribution measurements. Plasma temperature is sustained at less than 40 °C and abundant amounts of reactive species, which are important agents for bacteria inactivation, are detected over the entire plasma region. Large area treatment ability of this newly developed device is verified through bacteria inactivation experiment using E. coli. Sterilization experiment shows a large bacterial killing mark of 25 mm for a plasma treatment time of 10 s.

Microwave-excited atmospheric-pressure plasma jets using a microstrip line

We report a 2.45GHz microwave-excited atmospheric-pressure plasma jet (MW-APPJ) device using a microstrip line for materials processing. A three-dimensional simulation based on the finite difference time domain method revealed that the configuration of the MW-APPJ device results in a strong concentration of electric fields at the gas nozzle. Argon plasmas were generated at the nozzle and were blown into ambient air with the maximum length of 5mm at a microwave power of 40W. The rotational temperatures of molecular nitrogen in the downstream of the plasma jets, measured by optical emission spectroscopy, were 1720to900K for gas flow rates from 0.5to3.5l∕min, indicating that the jets were nonthermal plasmas. This MW-APPJ device will provide a large-area APPJ for materials processing depending on the configuration of the nozzle array and microstrip lines.

Decomposition and polymerization of perfluorinated compounds in microwave-excited atmospheric pressure plasma

Decompositions and polymerizations of perfluorinated compounds gases were demonstrated employing atmospheric pressure plasmas with continuous-wave microwave excitations. The atmospheric pressure plasma was generated at a low gas temperature of 520 K. Spherical-shaped particles of approximately 50–120 nm in diameter were synthesized in CF4∕He and C4F8∕He plasma on Si substrate with dc voltage biasing, which was set in the plasma downstream region. The gas temperature in plasma was important to generate particles because particles were not generated at a high gas temperature of 850 K. The particles were determined to consist of carbon and fluorine atom composition from an energy dispersive x-ray spectroscopy. Furthermore, the effect of H2 addition on the CF4∕He plasma was investigated. The decomposition efficiency of CF4 was increased with H2 addition and obtained over 80% without emissions of carbon dioxide.