The plasma of several different gases has shown a sporicidal activity. From these gases, nitrogen gas was most difficult to produce atomic nitrogen radicals. However, these radicals have a high energy, indicating that nitrogen gas plasma could be used to sterilize microorganisms and inactivate endotoxins. The sterilization mechanism of nitrogen gas plasma is the synergistic effect of a high rising-up voltage pulse, UV irradiation and atomic nitrogen radicals. Thus, the target cells were damaged by degradation, which resulted in death. The biological indicator (BI) used in this study was Geobacillus stearothermophilus ATCC 7953 at a population of 1 x 106 CFU/sheet. Sterility assurance was confirmed by using the Bl. Moreover, endotoxins were successfully inactivated. More than 5 log reduction of endotoxins could be attained with 30 minutes of nitrogen gas plasma exposure. Material functionality influenced by nitrogen gas plasma presented a satisfactory result. No deterioration of polymers could be observed by nitrogen gas plasma exposure.

Carbon nanowalls (CNWs), which are vertically oriented multi-layer graphene sheets, were employed in surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) measurements to detect low-molecular-weight organic compounds. CNWs substrates with widely different wall-to-wall distances from 142 to 467 nm were synthesized using a radical-injection plasma-enhanced chemical vapor deposition (RI-PECVD) system with nanosecond pulse biasing to a sample stage. When survival yield (SY) values of N-benzylpyridinium chloride (N-BP-Cl) were examined, which is commonly used to evaluate desorption/ionization efficiency, a narrower wall-to-wall distance presented a higher SY value. The highest SY value of 0.97 was realized at 4 mJ/cm2 for the highest-density CNWs with a wall-to-wall distance of 142 nm. The laser desorption/ionization effect of arginine, an amino acid, was also investigated. When CNWs with a narrower wall-to-wall distance were used, the signal-to-noise (SN) ratios of the arginine signals were increased, while the intensity ratios of fragment ions to arginine signals were suppressed. Therefore, the CNWs nanostructures are a powerful tool when used as a SALDI substrate for the highly efficient desorption/ionization of low-molecular-weight biomolecules.

The mechanism of action on biomolecules of N 2 gas plasma, a novel sterilization technique, remains unclear. Here, the effect of N 2 gas plasma on protein structure was investigated. BSA, which was used as the model protein, was exposed to N 2 gas plasma generated by short-time high voltage pulses from a static induction thyristor power supply. N 2 gas plasma-treated BSA at 1.5 kilo pulses per second showed evidence of degradation and modification when assessed by Coomassie brilliant blue staining and ultraviolet spectroscopy at 280 nm. Fourier transform infrared spectroscopy analysis was used to determine the protein's secondary structure. When the amide I region was analyzed in the infrared spectra according to curve fitting and Fourier self-deconvolution, N 2 gas plasma-treated BSA showed increased a-helix and decreased b-turn content. Because heating decreased a-helix and increased b-sheet content, the structural changes induced by N 2 gas plasma-treatment of BSA were not caused by high temperatures. Thus, the present results suggest that conformational changes induced by N 2 gas plasma are mediated by mechanisms distinct from heat denaturation.

We have recently treated with N2 gas plasma and achieved inactivation of bacteria. However, the effect of N2 gas plasma on viruses remains unclear. With the aim of developing this technique, we analyzed the virucidal effect of N2 gas plasma on influenza virus and its influence on the viral components. We treated influenza virus particles with inert N2 gas plasma (1.5 kpps; kilo pulses per second) produced by a short high-voltage pulse generated from a static induction thyristor power supply. A bioassay using chicken embryonated eggs demonstrated that N2 gas plasma inactivated influenza virus in allantoic fluid within 5 min. Immunochromatography, enzyme-linked immunosorbent assay, and Coomassie brilliant blue staining showed that N2 gas plasma treatment of influenza A and B viruses in nasal aspirates and allantoic fluids as well as purified influenza A and B viruses induced degradation of viral proteins including nucleoprotein. Analysis using the polymerase chain reaction suggested that N2 gas plasma treatment induced changes in the viral RNA genome. Scanning electron microscopy analysis showed that aggregation and fusion of influenza viruses were induced by N2 gas plasma treatment. We believe these biochemical changes may contribute to the inactivation of influenza viruses by N2 gas plasma.

Here we show that N₂ gas plasma, produced by applying a short high-voltage pulse using a static induction (SI) thyristor power supply inactivates influenza virus. N₂ gas plasma treatment of influenza A and B viruses induced the degradation of viral proteins, including nucleoprotein, hemagglutinin, and neuraminidase. The injury of viral RNA genome and the inactivation of hemagglutination were also observed after N₂ gas plasma treatment. These changes were possibly due to changes in the viral envelope, because modification of the lipid content was also suggested by Fourier-transformed infrared spectroscopy. At least three major mechanisms of action (heat, UV-A, and oxidative stress (i.e. hydrogen peroxide-like molecules)) were found in this system. Among them, oxidative stress appeared to be the main factor in the inactivation of influenza virus. In addition, there was an increase in the nitrotyrosine content of viral proteins, suggesting that oxidative stress produced by N₂ gas plasma generation oxidized proteins. As a result, oxidation may be the most important factor in the inactivation, degradation, and modification of influenza virus by N₂ gas plasma.