Electron paramagnetic resonance (EPR)-spin trapping and flow cytometry were used to identify free radicals generated using argon-cold atmospheric plasma (Ar-CAP) in aqueous solutions and intracellularly in comparison with those generated by X-irradiation. Ar-CAP was generated using a high-voltage power supply unit with low-frequency excitation. The characteristics of Ar-CAP were estimated by vacuum UV absorption and emission spectra measurements. Hydroxyl (·OH) radicals and hydrogen (H) atoms in aqueous solutions were identified with the spin traps 5,5-dimethyl-1-pyrroline N-oxide (DMPO), 3,3,5,5-tetramethyl-1-pyrroline-N-oxide (M4PO), and phenyl N-t-butylnitrone (PBN). The occurrence of Ar-CAP-induced pyrolysis was evaluated using the spin trap 3,5-dibromo-4-nitrosobenzene sulfonate (DBNBS) in aqueous solutions of DNA constituents, sodium acetate, and L-alanine. Human lymphoma U937 cells were used to study intracellular oxidative stress using five fluorescent probes with different affinities to a number of reactive species. The analysis and quantification of EPR spectra revealed the formation of enormous amounts of ·OH radicals using Ar-CAP compared with that by X-irradiation. Very small amounts of H atoms were detected whereas nitric oxide was not found. The formation of ·OH radicals depended on the type of rare gas used and the yield correlated inversely with ionization energy in the order of krypton > argon = neon > helium. No pyrolysis radicals were detected in aqueous solutions exposed to Ar-CAP. Intracellularly, ·OH, H2O2, which is the recombination product of ·OH, and OCl- were the most likely formed reactive oxygen species after exposure to Ar-CAP. Intracellularly, there was no practical evidence for the formation of NO whereas very small amounts of superoxides were formed. Despite the superiority of Ar-CAP in forming ·OH radicals, the exposure to X-rays proved more lethal. The mechanism of free radical formation in aqueous solutions and an intracellular milieu is discussed.

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Free radical species in aqueous solution-various alcohol-water reaction mixtures-by exposure to non-equilibrium cold atmospheric pressure Ar plasma (CAP), were monitored using electron paramagnetic resonance spin-trapping techniques with 3, 5-dibromo-4nitrosobenzene sulfonate as a water soluble nitroso spin trap. The major radical species were formed by H-abstraction from alcohol molecules due to •OH radicals. In the ethanol-water mixture •CH 2 CH 2 OH produced by H abstraction from CH 3 group of the ethanol and •CH 3 radicals were detected. The latter was due to the decomposition of unstable CH 3 •CHOH to form the •CH 3 radicals and the stable formaldehyde by C-C bond fission. These intermediates are similar to those observed by reaction with •OH radicals generation in the H 2 O 2 -UV photolysis of the reaction mixtures. The evidence of •CH 3 radical formation in the pyrolytic decomposition of the reaction mixtures by exposure to ultrasound or in methane irradiated with microwave plasma have been reported previously. However, the pyrolytic •CH 3 radicals were not found in both plasma and H 2 O 2 -UV photolysis condition. These results suggests that free radicals produced by Ar-CAP are most likely due to the reaction between abundant •OH radicals and alcohol molecules.

Cold atmospheric pressure plasma (CAP) is known as a source of biologically active agents, such as reactive oxygen species (ROS) and reactive nitrogen species (RNS). In the present study, we examined the effects of nitrogen (N2) on the apoptosis of and changes in gene expression in human lymphoma U937 cells exposed to argon (Ar)-CAP. Enormous amounts of hydroxyl (·OH) radicals in aqueous solution were produced using Ar‑CAP generated using a 20 kHz low frequency at 18 kV with a flow rate of 2 l/min. The increase in the levels of ·OH radicals was significantly attenuated by the addition of N2 to Ar gas. On the other hand, the level of total nitrate/nitrite in the supernatant was significantly elevated in the Ar + N2-CAP‑exposed U937 cells. When the cells were exposed to Ar‑CAP, a significant increase in apoptosis was observed, whereas apoptosis was markedly decreased in the cells exposed to Ar + N2-CAP. Microarray and pathway analyses revealed that a newly identified gene network containing a number of heat shock proteins (HSPs), anti-apoptotic genes, was mainly associated with the biological function of the prevention of apoptosis. Quantitative PCR revealed that the expression levels of HSPs were significantly elevated in the cells exposed to Ar + N2-CAP than those exposed to Ar‑CAP. These results indicate that N2 gas in Ar‑CAP modifies the ratio of ROS to RNS, and suppresses the apoptosis induced by Ar‑CAP. The modulation of gaseous conditions in CAP may thus prove to be useful for future clinical applications, such as for switching from a sterilizing mode to cytocidal effect for cancer cells.

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Lithium niobate (LN) etching has been demonstrated with an electron cyclotron resonance (ECR) plasma and low-frequency bias. The etching was studied by using Ar, BCl 3 and SF 6 gases. The etch rates of BCl 3 and SF 6 are about 3.8 and 4.6 times higher than that of Ar, respectively. The highest etch rate (220 nm/min) was obtained under the condition of SF 6 plasma and 1 MHz bias. The etching method which can fabricate micro-trenches with high-aspect ratio and smooth surfaces has been achieved.

We have developed a growth system for carbon nanotubes (CNTs) based on an alcohol thermal chemical vapor deposition (A CVD). This system, which is similar to a cold wall-type CVD system, has an additional tubular electric furnace. The additional furnace is installed at a gas inlet in order to heat the carbon source gas. In this study, we have investigated the eŠect of the gas inlet heating to the grown CNTs by Raman spectroscopy and scanning electron microscopy (SEM). It was found that the smaller diameter singlewalled CNTs (SWCNTs) could be grown with a gas inlet heating at 800°C compared to the grown SWCNTs obtained without gas inlet heating. The two-furnace A CVD system can provide a new method of a diameter-controlled growth of SWCNTs.