Introduction and Application of Microplasma
Yuki KOMURO, Hodaka FUKUNAGA, Shigeki TATEMATSU,
Marius BLAJAN and Kazuo SHIMIZU
Innovation and Joint Research Center, Shizuoka University, Jouhoku, Hamamatsu, 432-8561, Japan
E-mail：shimizu@cjr.shizuoka.ac.jp

INTRODUCTION
Microplasma can be generated only around 1 kV at
atmospheric pressure. It has possibilities ofreplacement technology of traditional one and has
been intensively studied for various application
fields, since this technology. One bio/medical
application of microplasma is “sterilization”. The
sterilization process was carried out with activespecies generated between the electrodes. Surface
treatment with long life active species for glass,polymer and other materials could be also possible.

METHODS(1)Sterilization process and electrodes

O2

Fig. 4 shows experimental setup for sterilization ofE.coli and B. subtilis. The liquid culture medium wasintroduced in the microplasma reactor and sprayed
at a gas flow rate of 3.5 L/min, through theelectrode against a petri dish with culture medium.
Total gas flow rate was 8.5 L/min. Sprayed bacteriawith liquid culture medium was sterilized between
microplasma electrodes.

H2ON2OH*O3O3O(1D)OH*1 mm(a) Before treatment (b) Ar microplasma 650 V
Fig. 9 Image of E. coli before and after Ar microplasma
treatment(x7,000).

(1) Sterilization result [○]Spacer
100 nm

100 mmArI

1 mmRESULTS

Ar or airAr

(3) FE-SEM images of bacteria

Fig. 3 shows experimental setup for sterilization ofE. coli. E. coli was diluted in the liquid medium andthe culture medium was applied on the agar medium.
Then the agar medium was inserted in themicroplasma reactor and exposed to remote
microplasma. The distance between agar medium andelectrodes could be adjusted by Z-axis stage.

OH*

OH*

N2(A)

100 nm(a) Before treatment (b) Ar microplasma 650 V
Fig. 10 Image of Alicyclobacillus before and after Ar
microplasma treatment(x30,000).

OH*Agar(a) Sterilization process(b) Image of microplasma
Fig. 1 Sterilization process and image of microplasma
during discharge.
Fig. 1 shows the electrodes and sterilization process.
Electrodes are perforated metal plates covered witha dielectric layer and faced together. Microplasma
was generated between the electrodes by the applied
voltage thus active species and radicals wereproduced according to gas composition. Table 1
shows the detail of electrodes.

(a) No treatment(b)Ar microplasma 850V
Fig. 5 The experiment result of sterilization byusing Ar microplasma. Treatment time was 60 s,distance between electrodes and E. coli was 2 mm.

(a) Before treatment (b) Ar microplasma 650 V
Fig. 11 Image of B. subtilis before and after Air
microplasma treatment(x30,000).

(2) Image of streamer of discharge
Grounded electrode

100 µmHigh voltage electrode(negative)(a) Electrode surface (b) Streamer from discharge
Fig. 2 Image of a streamer from microplasma
discharge.
Microplasma is typically dielectric barrier discharge.
The image of emitting of streamer is shown in fig. 2.
Streamer diameter is thinner than previously
reported.

100 nm

100 nm(a) No treatment(b)Air microplasma 1.5 kV
Fig. 6 The experiment result of sterilization byusing air microplasma. Treatment time was 60 s,distance between electrodes and E. coli was 2 mm.
Figs. 5 and 6 show the sterilization result of E. coli.
Ar microplasma treatment could sterilize near thecenter of Petri dish. However, Air microplasma
treatment could sterilize more widely area than Ar
one. This could be due to the long lifetime active
species derived from O2.

Fig. 9 shows the image of E. coli which was thenursing cell state and Fig. 10 shows the image ofgram-positivebacteria
Alicyclobatillus
acidoterrestris was spore state taken by SEM. Fig.
11 shows the image of B. subtilis spore E. coli and
Alicyclobatillus were physically damaged by applying
microplasma as shown in Figs. 9, 10 and Fig. 11(right).

(4) Effect on the living body by microplasma
GasMicroplasma
electrodes(2) Sterilization result [●]Human skin(3) Experimental Setup

Fig. 12 Image of Microplasma exposure to humanskin.

(a) No treatment(b)Air microplasma 1.4 kV
Fig. 7 The experiment result of sterilization byusing air microplasma (B. subtilis).

84.4°

55.6°

(a) Before treatment(b) After treatment
Fig. 13 Contact angle of water droplet on thehuman skin before(left)and after the microplasma
treatment(right). (Ar gas, Vd=650 V, treatment
time: 30 s).

Fig. 3 Experimental setup [○]Fig. 8 The experiment result of sterilization byusing air and nitrogen microplasma (B. subtilis).

Fig. 4 Experimental setup [●]Various active spices generated by microplasma
such as ions, and metastable molecules has beentreated to the human skin as shown in Fig. 12.

Sterilization rate by nitrogen plasma was lower
compared to the rate of Air plasma.
The sterilization process according with thisresults, could be considered synergetic effect of UV
radiation, high electric field, (not only oxidative)
radicals, and ozone.

Fig. 13 shows surface treatment for human skinby microplasma treatment. Human skin’s contact
angle was decreased. Electrical damage to sample
could not be considered because the electric field
was closed between electrodes.

Conclusion
In this study, we are presenting the introduction
and application of microplasma. Various application
could be considered to the many fields i. e.
sterilization process surface treatment and forplasma medicine. We will try to develop useful andsafety microplasma process.