Introduction and Application of Microplasma
Kazuo SHIMIZU, Shigeki TATEMATSU, Marius BLAJAN, and Hodaka FUKUNAGA
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 the possibility toreplace traditional technologies and has been
intensively studied for various application fields. One
bio/medical
applicationofmicroplasma
is“sterilization”. The sterilization process wascarried out with active species generated between
the electrodes. Surface treatment with long life
active species for glass, polymer and other materials
could be also possible.

METHODS

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.

(1) Electric Characteristics
Discharge voltage

GNDGND
1 kV/div

1 kV/div

10 ms/div(1)Sterilization process and electrodes

10 ms/div

Discharge current

Discharge current

Ar or air

GNDGNDAr

O2

H2O

N2

OH*O3

O3O(1D)

OH*OH*

OH*

100 mA/div
10 ms/div

Spacer100 nm

10 ms/div(a) Ar microplasma(b) Air microplasma
Fig. 4 current-voltage characteristic

N2(A)Spike-like currents occurred at the steepest slopesof the discharge voltage. This is a typical waveformof dielectric barrier discharge.

OH*Agar(a) Sterilization process(b) Image of microplasma
Fig. 1 Sterilization process for E. coli and image of
microplasma during discharge.

(2) Sterilization result

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 1shows the detail of electrodes.
Table 1 The detail of electrodes.
Diameter
Hole diameter
Aperture ratio
Discharge gap
Discharge area
Gas flow rate

100 nm

100 mA/div

100 mmArI

1 mm(a) Before treatment (b) Ar microplasma 650 V
Fig. 7 Image of E. coli before and after Ar microplasma
treatment(x7,000, treatment time 60 s).

RESULTS
Discharge voltage

1 mm(a) Before treatment (b) Ar microplasma 650 V
Fig. 8 Image of Alicyclobacillus before and after Ar
microplasma treatment(x30,000, treatment time 60 s).

Fig. 7 shows the image of E. coli which was thenursing cell state and Fig. 8 shows the image ofgram-positivebacteria
Alicyclobatillus
acidoterrestris was spore state taken by SEM. E.
coli and Alicyclobatillus were physically damaged byapplying microplasma as shown in Figs. 7 and 8(right).

(3) Surface treatment by microplasma(a) No treatment(b)Ar microplasma 650V

45 mm
1.6 mm
30％
100 mm
100 mm2
10 L/min(2) Image of streamer of discharge
Grounded electrode

100 µm(c)Ar microplasma 750V(d)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.

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

(3) Experimental Setup

Fig.9 Relationship between treatment time andcontact angle. (Discharge voltage -1.3 kV, distance
between electrodes and PEN film1 mm, gas flowrate 5 L/min)Fig. 9 shows characteristics between treatment
time and contact angle. Marx generator circuit wasused as power supply and it can generate pulse
high voltage. Initial contact angle of PEN film wasabout 73゜. The minimum contact angle of about
30゜ was obtained at treatment time of 20 sec.

(4) Effect on the living body by microplasma

84.4°(a) No treatment

55.6°(b)Air microplasma 1.3 kV(a) Before treatment(b) After treatment
Fig. 10 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).

(c)Air microplasma 1.4 kV (d)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.

Fig. 3 Experimental setup

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. 10 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.
In this study, we are presenting the introduction
and application of microplasma. Characteristics ofmicroplasma is similar to that of the other non
thermal plasma except streamer diameter. 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.