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CHAPTER 3 RELATIVE INFLUENCE OF PLASMA INACTIVATION AGENTS ON BACTERIAL SPORES IN CONTINUOUS WAVE RF 3.1 Introduction OXYGEN DISCHARGES Microorganism inactivation by plasma treatment has stirred a great interest in the recent years. Oxygen and oxygen-based plasmas proved to be effective for the inactivation of highly resistant microorganisms, especially of the sporulate ones [15-18, 37, 57-61]. Radio-frequency driven plasma devices using these gases at low, medium and atmospheric pressure have been developed and tested for their potential as alternative technologies to the existing conventional sterilization techniques [15-18, 42, 60, 62-64]. Although plasma as a sterilization tool has proved its advantages over the thermal and chemical ones, the precise inactivation mechanism is still not known, many suppositions being advanced in the last years [15, 17, 37, 50, 57, 60, 61, 65, 66]. Some works give credit to the optical radiation as being the dominating inactivation agent, [16-18, 37, 57, 67] others state that 41
the reactive species from plasma are responsible for bacteria inactivation, [15, 60, 62, 64, 65, 68, 87, 97] and another category of studies propose an explanation based on the synergy of the above two [17, 18, 57, 60, 64, 65, 69, 88]. Regardless of the tentative microbial decontamination mechanisms already proposed, it is clear that plasma acts on bacteria with all its three inactivation agents: heat, optical radiation, and plasma particles (i.e., electrons, ions and neutrals). In the last years there have been a few attempts to assess the relative effectiveness of these inactivation agents in low pressure [61, 69] and atmospheric pressure discharges [68]. However, the number of studies on this topic is still very small and the reported results are obtained under highly different experimental conditions to allow comparisons and/or rule out controversies. The aim of this chapter is to evaluate the relative effects of each of the above mentioned plasma inactivation agents. In order to study the dynamics of spore inactivation, the survival curves (i.e., the number of surviving spores as a function of the treatment time) were traced for different injected RF powers. Using the obtained survival curves, the extracted information allowed to establish the separate contribution of each of the above three inactivation agents to the reduction of the viable spore number. These results indicated that during the initial stage of the plasma treatment of the spore contaminated samples, the most important inactivation agent is the optical radiation, whereas the second stage of treatment, the leading role is taken over by plasma particles. Moreover, the RF power sensitivity 42
Page 1 and 2: PLASMA STERILIZATION USING LOW PRES
Page 3 and 4: my appreciation especially for the
Page 5 and 6: Iis ion saturation current [µA] t
Page 7 and 8: CONTENTS 1 PRINCIPLES OF SURFACE DI
Page 9 and 10: 4 EFFECTS OF LOW TEMPERATURE PULSED
Page 11 and 12: and intuited to bring new important
Page 13 and 14: Figure 1.1: Schematic representatio
Page 15 and 16: Table 1.1: Common disinfection and
Page 17 and 18: the radiation energy is resonantly
Page 19 and 20: ers of heat, optical radiation and
Page 21 and 22: Table 1.2: Main plasma sources used
Page 23 and 24: microorganism population as a respo
Page 25 and 26: UV Photon Before After DNA Figure 1
Page 27 and 28: to sterilize medical tools, but the
Page 29 and 30: sented by both theoretical and expe
Page 31 and 32: Plasma Sterilization Using Low Pres
Page 33 and 34: Figure 2.1: Experimental set-up. MB
Page 35 and 36: Figure 2.3: Electronic circuit of t
Page 37 and 38: such circumstances, the inactivatio
Page 39 and 40: ment time t is N = N0e −αt ≡ N
Page 41 and 42: shows the number of the viable micr
Page 43 and 44: has n −1 0 > 281.25 µm 2 availab
Page 45 and 46: 1 st 2 nd ( I) TNTC (II) TNTC (III)
Page 47 and 48: U LC blocking filter 19.74 pF 20.24
Page 49: Figure 2.8: Experimental set-up use
Page 53 and 54: Temperature measurement Relative in
Page 55 and 56: MR MP SH Figure 3.2: Experimental a
Page 57 and 58: a fast temperature increasing rate.
Page 59 and 60: D h (min) 10 3 10 2 10 1 10 0 100 2
Page 61 and 62: MR QP SH Figure 3.6: Experimental a
Page 63 and 64: The contribution of photons and hea
Page 65 and 66: D (min) 10 3 10 2 10 1 10 0 Dν D h
Page 67 and 68: N/N 0 (%) 10 2 10 2 10 2 10 2 10 2
Page 69 and 70: D (min) 10 2 10 1 10 0 D h+ν+p D h
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Page 73 and 74: 3.5 Power sensitivity of spore inac
Page 75 and 76: If for a reference treatment temper
Page 77 and 78: of the sample was achieved. Moreove
Page 79 and 80: microorganisms were disposed in mon
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Page 83 and 84: in chapter 2. The treatment time of
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Page 87 and 88: ton =500µs, and the duty cycle was
Page 89 and 90: T ( 0 C) 120 100 80 60 40 20 I 0 5
Page 91 and 92: N/N 0 (%) 10 2 10 2 10 2 10 1 10 1
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I (arb. unit) 5 4 3 2 1 0 0.000 0.0
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I > (arb.unit) 1.0 0.9 0.8 0.7 0.6
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shown in Fig. 4.14. It can be seen
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I is (mA) 0.25 0.20 0.15 0.10 0.05
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value. When ton has been kept const
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survival curve characteristics were
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of the effects produced by differen
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solutely necessary for a profound u
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Conferences 1. Bacillus spores ster
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[9] W. A. Rutala, D. J. Weber, J. H
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[34] J. H. Young: Sterilization wit
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[57] M. K. Boudam, M. Moisan, B. Sa
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[79] J. Schneider, K. M. Baumgartne
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[100] S. Villeger, S. Cousty, A. Ri
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