AVS 49th International Symposium
    Plasma Science Tuesday Sessions
       Session PS-TuP

Paper PS-TuP30
Experimental Study on New Sterilization Process by using Plasma Source Ion Implantation Method with N@sub 2@ Gas

Tuesday, November 5, 2002, 5:30 pm, Room Exhibit Hall B2

Session: Plasma Applications
Presenter: T. Tanaka, Hiroshima Institute of Technology, Japan
Authors: M. Yoshida, Mitsubishi Heavy Industries, Ltd., Japan
T. Tanaka, Hiroshima Institute of Technology, Japan
S. Watanabe, Hiroshima Institute of Technology, Japan
T. Takagi, Hiroshima Institute of Technology, Japan
M. Shinohara, Kurita Seisakusho Manufacturing Co., Ltd., Japan
S. Fujii, Adtec Plasma Technology Co., Ltd., Japan
Correspondent: Click to Email
Plasma source ion implantation (PSII) with negative high voltage pulses has been applied to uniform sterilization process for three-dimension shaped species. This process was performed with and without external plasma source, that has been generated by inductively coupled antenna using 222 kHz RF voltage. The pulsed high negative voltage (~10 µs pulse width, 300~900 pulses/sec, 9~16 kV) was applied to the electrode in this process at the gas pressure of 2~7 Pa of N@sub 2@. This process has been found out to be capable of generating glow discharge plasma around SUS electrode, on which quartz glass plate with biological materials are placed. We have obtained a preliminary result that the PSII process has reduced log numbers of Bacillus Pumilus with N2 gas plasma generated by pulsed RF and DC voltages. This experimental result is showing a 5~6 log@sub 10@ colony forming units reduction in Bacillus Pumilus with dried culture media by 5~10 minutes exposure. The effect of several discharge conditions such as gas pressure, pulse voltage, and RF power have been investigated experimentally. The RF discharge without negative high voltage pulses has been found to reduce colony forming units by ~3 log@sub 10@ for 40 minutes exposure as well. However, negative high voltage pulses are necessary to achieve 5~6 log@sub 10@ reduction of Bacillus Pumilus for ~5 minutes exposure. The state of Bacillus Pumilus on quartz glass was observed by scanning electron microscopy (SEM) with and without exposure, which is showing the surface of Bacillus Pumilus has some damage by the plasma treatment, and no damages are seen in Bacillus Pumilus by just setting in vacuum. From these experimental results, some possible effective options for the plasma sterilization systems are discussed, such as H@sub 2@O vapor mixture to generate dense OH radicals, Ar or He gas usage, and electron bombardment by the positive high voltage pulses.