23P004-O
Dry Etching of Escherichia coli by O2-, Ar-, Air-, and H2O- Plasma
O2-, Ar-, Air-, H2O-プラズマによる大腸菌のドライエッチング
Akihiro Matsutani1, Ayako Takada2
松谷晃宏 1，髙田綾子 2
1

Center for Semiconductor and MEMS Processes, Technical Department, Tokyo Institute of Technology
R2-3, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 Japan
東京工業大学 技術部 半導体・ＭＥＭＳ支援センター，〒226-8503 横浜市緑区長津田町 4259, R2-3
2Bio-Technical Center, Technical Department, Tokyo Institute of Technology
B-41, 4259 Nagatsuta, Midori-ku, Yokohama 226-8501 Japan
東京工業大学 技術部 バイオ技術センター，〒226-8501 横浜市緑区長津田町 4259, B-41We demonstrated a relationship between size of E. coli cells and O2 plasma irradiation time andcarried out SEM observation about dry etching of Escherichia coli cells by O2-, Ar-, Air-, and H2Oplasma. It was found that oxygen or argon ions contributed for the degradation of E. coli cells.

1. Introduction
Recently, the sterilization technique of bacteriausing plasma has been investigated with someplasma sources such as atmospheric pressureplasma, low-pressure discharge plasma and soon [1-3]. However, the mechanism ofdegradation of Escherichia coli has not beenclear. We investigated the etching gas species
dependence of the degradation of the E. colicells.
In this paper, we describe the etching behaviorof E. coli cells by O2-, Ar-, and H2O- plasma.

2. Relationship between size of Escherichia
coli cells and O2 plasma irradiation time
Generally, it is difficult to evaluate size change
every E. coli cell in plasma treatment of bacteria,
because it is difficult to identify one bacteria cellfrom among many bacteria cells in culture. We
can identify each bacteria cell by using themicroenclosure [4]. Figure 1(a) and 1(b) show
optical microscope images of degradation of E.
coli before and after O2 plasma etching,respectively. Figure 2 shows the relationshipbetween O2 plasma irradiation time and size of E.
coli cells. RF power was 100 W, O2 flow rate
was 25 sccm, process pressure was kept at 13.3
Pa and etching time was 30 sec. In this etchingcondition, E. coli cells were eliminated by O2
plasma etching of 120 sec.

(a)

10μm(b)10μm

Fig. 1 Optical microscope images of degradation ofE. coli by O2 plasma using microenclosure forsingle cell isolation: (a) before etching and (b) afteretching.

Fig. 2. Relationship between O2 plasma
irradiation time and size of E. coli cells.

3. Dry Etching of Escherichia coli byDischarge Plasma
We used a reactive ion etching system (SamcoRIE-1) and pure O2, Ar, Air as etching gases.
H2O plasma etching was performed bysupplying water vapor from ice placed on the RF
electrode in a process chamber [5]. In thisexperiment, E. coli K-12 strain W3110 was used.
We used E. coli cells dropped on Si substrate assamples. Figure 3(a)-3(d) show SEM images ofE. coli etched by O2-, Ar-, Air- and H2O- plasma,respectively. In Fig. 3(a)-3(c), the RF power was
100 W, O2-, Ar- and Air- flow rate was 25 sccm
and process pressure was kept at 13.3 Pa. In Fig.
3(d), the process pressure was at 27 Pa. We
confirmed that E. coli cells were not etched by O
radicals in this etching condition. E. coli cells
were mainly etched by ions because they wereplaced on the RF electrode. In Fig. 3(a), it isfound that E. coli cells were etched by oxygenion. In Fig. 3(b), it is found that E. coli cells
were etched by Ar ion. E. coli cells weredegraded by Air plasma including O2 of 20% asshown in Fig. 3(c). While, E. coli cells were notalmost etched by H2O plasma including H, OHand O as shown in Fig. 3(d). Oxygen ratio in
H2O plasma was smaller than that in O2- or Airplasma [6]. We think that yields of etching andsputtering for E. coli by hydrogen was muchsmaller than that of oxygen , because the massof hydrogen is smaller than that of oxygen.
4. Conclusions
We demonstrated a relationship between sizeof E. coli cells and O2 plasma irradiation timeand carried out SEM observation about dry
etching of E. coli cells by O2-, Ar-, Air-, andH2O- plasma. It was found that O or Ar ionscontributed for the degradation of E. coli cells.

(a)

(b)

(c)

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50 (2011) 06GG07.
[5] A. Matsutani, H. Ohtsuki and F. Koyama: Jpn. J.
Appl. Phys. 47 (2008) 5113.

(d)Fig. 3 SEM images of E. coli cells etched bydischarge plasma: (a) O2 plasma, (b) Arplasma, (c) Air plasma and (d) H2O plasma.