Analyses of chemical composition on bacteria surface treated in atmospheric pressure plasmas

Analyses of chemical composition on bacteria surface treated in atmospheric pressure plasmas

Analyses of Chemical Composition on Bacteria Surface Treated in

Atmospheric Pressure Plasmas

大気圧プラズマで処理した細菌表面における化学組成解析

Shohei Yoshida, Tadashi Fukuda, Kazuo Takahashi, Takuya Urayama*, Shinji Aoki**

Department of Electronics, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan

京都工芸繊維大学大学院工芸科学研究科電子システム工学専攻，〒606-8585 京都市左京区松ヶ崎

* Adtec Europe Ltd., London

**Adtec Plasma Technology Co.,Ltd, 6-10, 5-chome Hikino-cho, Fukuyama City, Hiroshima, 721-0942, Japan

（株）アドテックプラズマテクノロジー，〒721-0942 広島県福山市引野町五丁目6番10号

The sterilization mechanism was analyzed in atmospheric plasmas It was confirmed that the cell wall of

G.stearothermophilus exposed to plasmas was elapsed observing with scanning electron microscope

(SEM) From the x-ray photoelectron spectroscopy (XPS) spectra, the content of -CH2-CH2- bond decreased, and then the signal from O 1S increased with plasma exposure Analyses of SEM photographs and XPS spectra would mean that the cell wall of bacteria was oxidized and damaged with plasma exposure

1 Introduction

We have been studied about sterilization

mechanism of bacteria, investigating the cellulose

and bacteria on paper strip exposed to plasmas

Cellulose composed of pyranose rings was a model

material of peptidglycan corresponding to major

content of bacteria cell wall Exposing plasmas to

cellulose caused pyranose rings to be opened and

ring chains to be cleaved (Fig 1) The changes of

chemical bond composition in pyranose rings

correspond to damages of sugar chain on the

bacteria cell wall, which results in killing bacteria

Besides we confirmed that it was possible to

sterilize bacteria on paper strip with in our

atmospheric plasmas setup

In this study we observe bacteria

(G.stearothermophilu ATCC 7953) on Si substrate

coated by Au using scanning electron microscope

(SEM) For analysis of chemical composition on

bacteria surface we make use of x-ray photoelectron

spectroscopy (XPS) and evaluate how bacteria

Fig.1 Schematic for changing of pyranose ring structure

surface changes by exposed to plasmas In all experiments, bacteria are treated with not only plasmas but also heatgun to be investigated the effect of heat from plasmas

2 Experiment

Figure 2 shows the schematic of the experimental setup Atmospheric pressure plasmas were generated by applying 2.45 GHz microwave power

to a metal rod as an antenna in the plasma torch A stub tuner was used for matching the microwave power Ar gas was introduced to the torch

Samples of bacteria (G.stearothermophilus

ATCC 7953) on Si substrate deposited Au (5 5

mm2) was treated with Ar gas flow rate of 3.5 slm, plasma exposure time of 10 min, distance from antenna to sample of 10 mm, and microwave power

of 70 W In order to investigate the effect of heat from plasmas, we treated bacteria with heated air flow (200°C) from heatgun in the experimental conditions same as in case of plasmas

The XPS was employed for chemical analyses on bacteria surface On the other hand, the effect of plasma on sterilization was evaluated in observation

of bacteria using SEM In addition, we measured optical emission spectra of plasmas to investigate the sterilization mechanism

Opening of pyranose ring Cleaving of pyranose ring chain

OH

N 2

Ar

O 2

Fig.2 Schematic of setup for atmospheric plasmas

Fig.3 SEM photograph of bacteria.

3 Results and Discussions

3.1 SEM photograph of bacteria

Figure 3 shows bacteria exposed plasmas The

bacterium of left side in Fig 3 has an ellipsoidal

shape and looks like to be partly ruptured One of

right side in Fig 3 looks like to be destroyed

completely Thus we can understand that burst of

cell wall or cell membrane happens in the Fig 3

The one treated with heatgun did not change in

SEM observation

3.2 XPS spectra of bacteria

Figure 4 shows XPS spectra on the bacteria

surface The original (pre-treatment) surface is

known to have several chemical bond components

of (-C(=O)-NH- or –O-C-O-), -C-OH, -CH2-CH2-,

and -C-C- (Fig 4(a)), since the predominant

constituents of bacteria surface are hydrocarbon

followed by polysaccharides and peptides [1] After

the plasma treatment, the chemical bond of

-CH2-CH2- disappeared on the surface (Fig 4(b)) It

seems that hydrogen was disorbed from the cell

wall, and the wall was oxdized and damaged in the

plasma treatment We could not find any changes in

the XPS spectra of bacteria treated with heatgun

3.3 Optical emission spectrum

Figure 5 shows optical emission spectrum from

plasma discharge The signals from OH, N2, and O

were obserbed as well as that from Ar Several

species coming from atmospheric may be candidate

for reactants on the cell wall

Fig.4 XPS spectra on the bacteria surface.

Fig.5 Optical emission spectrum in the plasma

(Ar: 7 slm, Power: 50 W).

4 Summary

We analysed the sterilization mechanism with SEM photograph, XPS spectra of bacteria (G.stearothermophilu), and Optical emission spectrum of plasma The cell wall of bacteria could

be ruptured by plasma exposure The chemical bond of -CH2-CH2- disappeared and O-content increased These cahnges in chemical bond compositions corresponded to oxidization and damages of the cell wall On the other hand, the effect of heat from plasmas did not related to rupture of bacteria In plasmas, several species of excited Ar and those from atmosphere may be candidate for the reactants of sterilization

References

[1] Jess J Ojeda, Mara E Romero-Gonzlez, Robert G Edyvean, and Steven A Banwart ‘Characterization

of the Cell Surface and Cell Wall Chemistry of Drinking Water Bacteria by Combining XPS, FTIR Spectroscopy, Modeling, Potentiometric Titrations’ Langmuir 4032-4040, 24 (8) 2008

Ar Plasma

Torch

Silica Tube Bacteria

2.45 GHz Tuner