プラズマエレクトロニクス分科会会報 No.56 - 応用物理学会

characterization and bacteria destruction as the aspect
of inactivation mechanism via the synergetic effect
due to radicals and VUV/UV photons in N 2 /O 2
plasma[4]. The main results of the works mentioned
above are summarized as follow:
・In air-simulated plasma, the lethal damage is caused
by both effects, etching effect due to radical species
and VUV/UV photons, with highest efficacy.
・The MID (multiple ion detection) measurement of
QMS and shutter control system proved useful for
monitoring the bacteria degradation process, the
signals of H 2 O and CO 2 as main by-products
expressed a well defined corresponding to erosion of
bacteria by oxygen radicals, as shown in Fig.3.
Fig. 3 Time evolution of QMS signals for H 2 O and
CO 2 components during plasma irradiation[3].
・The higher input power was used, the more rapid
inactivation of the spores was observed.
・In N 2 /O 2 plasma, the best etching efficiency was in
the case of 90% O 2 /10% N 2 plasma, and etching
efficiency in rich oxygen mixture plasma were better
than pure O 2 plasma.
・As for the efficient inactivation of spores, we found
that the optimum gas mixture ratio was between 30
and 80%, as shown in Fig. 4. This result apparently
shows that the spores are inactivated by the synergetic
effect due to etching and VUV/UV photons.
3. Future Scope
Although much work has been done, there are still
many tasks needed to do. The understanding of the
interaction of plasma with living cells in general, and
with bacterial cell in particular, requires a careful
investigation which probes the effects on the cellular
and sub-cellular levels. So, an in-depth or systematic
study on the specific effects of the plasma on
sub-cellular components such as nucleoid, cytoplasm,
ribosome, etc. has yet to emerge. A lot of careful work
requiring collaborative efforts between plasma
physicists, microbiologists, and biochemists remains
to be done. Our goal in the study of low-temperature
plasma sterilization is to develop a commercial plasma
sterilizer for medical application.
Fig.4 Survival curves for G. stearothermophilus
samples exposed to N 2 /O 2 plasma 20s and 60s,
respectively, as a function of oxygen mixture ratio [3].
References
[1] M. Nagatsu, F. Terashita, and Y. Koide: Jpn. J.
Appl. Phys. 42 (2003) 856.
[2] M. Nagatsu, F. Terashita, H. Nonaka, L. Xu, T.
Nagata, and Y. Koide: Appl. Phys. Lett. 86 (2005)
211502.
[3] Y. Zhao, A. Ogino, M. Nagatsu, Jpn. J. Appl. Phys.
50 (2011) 08JF05.
[4] Y. Zhao, A. Ogino, M. Nagatsu, Appl. Phys. Lett.,
98 (2011) 191501.
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