Tatsuyuki Nakatani

Sterilization mechanism for Escherichia coli by plasma flow at atmospheric pressure

A mechanism for sterilizing Escherichia coli by a flowing postdischarge and UV radiation of argon plasma at atmospheric pressure was investigated by analyzing the surviving cells and the potassium leakage of cytoplasmic material and by morphological observation. Inactivation of E. coli results from the destruction of the cytoplasmic membrane and the outer membrane under plasma exposure and the destruction of nucleic acids by exposure to ultraviolet radiation from the plasma source.

Inactivation of Escherichia Coli by a Coaxial Microwave Plasma Flow

An atmospheric low-temperature plasma flow generated by a microwave discharge utilizing a coaxial cable for microwave transmission was utilized for the inactivation of a bacteria. The employed device consists of a cavity, a quartz discharge tube, a coaxial cable, a microwave power source, and a gas supply system. Using this argon plasma source, we attempted to clarify the effects of exposure temperature, exposure time, exposure distance, input power, and gas flow rate on the number of surviving cells of Escherichia coli. A log reduction number of E. coli of at least 2 (10-2) was obtained at an exposure temperature of 353 K when the exposure time was 600 s with a gas flow rate of 5 Sl/min and an input power of 400 W. The number of surviving cells decreased with an increase of exposure time under any sterilization condition.

Characteristics of Nonequilibrium Plasma Flow and Its Sterilization Efficacy in a Tube at Atmospheric Pressure

A nonequilibrium plasma flow produced uniformly in a tube was developed in this paper. The plasma was generated in polyvinyl chloride tube, 3 mm in inner diameter and 100 mm in length, between a wire electrode, 0.2 mm in diameter, and a grounded flat electrode located at the bottom of the tube. We investigated the spectrum, temperature, and ozone concentration of this plasma flow and its sterilization efficacy against Geobacillus stearothermophilus. The temperature in the tube showed uniformity along the wire electrode and increases as applied voltage was increased. With a wire electrode temperature of 337 K at a peak-to-peak applied voltage of 10 kVpp in the sine wave and a frequency of 6 kHz, sterilization of 105 cells was obtained. This result suggests the potential of the application of plasma flow rather than ethylene oxide for sterilization of the inner wall of tubes, such as catheters and artificial blood vessels.

Effect of voltage polarity on oxidation-reduction potential by plasma in water

Use of plasma in water for water treatment and medical treatment is growing and raises expectations of finding advanced functions such as an increase of biological compatibility. In the present study with a focus on the variation of oxidation-reduction potential (ORP), relationships between the electrode polarities of plasma in water and the change of water quality such as conductivity, H2O2 concentration, dissolved hydrogen concentration, pH and ORP were revealed. Similar line spectra of radiation at the electrode tip were observed for each case of positive and negative electrode polarity. The emission intensities of OH (309 nm), Hα (656 nm), and OI (777 nm) for the positive discharge were significantly higher than those for the negative one, though the energy consumption during the discharge period of both cases was nearly the same. Positive electrode polarity was found to be more suitable than negative electrode polarity for increasing dissolved hydrogen gas and hydrogen peroxide. The ORP for the posit...

Study on Formation of Plasma Nanobubbles in Water

Nanobubbles of less than 400 nm in diameter were formed by plasma in pure water. Pre-breakdown plasma termed streamer discharges, generated gas channels shaped like fine dendritic coral leading to the formation of small bubbles. Nanobubbles were visualized by an optical microscope and measured by dynamic laser scattering. However, it is necessary to verify that these nanobubbles are gas bubbles, not solid, because contamination such as platinum particles and organic compounds from electrode and residue in ultrapure water were also observed.

Sterilization of Escherichia coli by a coaxial microwave plasma flow

An atmospheric low temperature plasma flow generated by microwave discharge utilizing a coaxial cable for microwave transmission has some advantages such as portability, simple configuration, and low power operation. It mainly consists of a cavity, a quartz discharge tube, a coaxial cable, a microwave power source and a gas supply system. Using this argon plasma source, we investigated to clarify effects of exposure temperature, exposure time, exposure distance, input power and gas flow rate on the number of surviving cells of Escherichia coli. A log reduction number of E. coli of at least 3 (10/sup -3/) was obtained at exposure temperatures of 353 K when the exposure time was 600 seconds with a gas flow rate of 5 Sl/min and an input power of 400 W. Number of surviving cells decreases with increase of exposure time in any sterilization conditions.