Pure Appl. Chem., Vol. 74, No. 3, pp. 349–358, 2002. © 2002 IUPAC
Plasma sterilization. Methods and mechanisms*
Michel Moisan1,‡, Jean Barbeau2, Marie-Charlotte Crevier3, Jacques Pelletier4, Nicolas Philip1, and Bachir Saoudi1
de physique des plasmas, Université de Montréal, B.P. 6128, Succursale Centre-ville, Montréal H3C 3J7, Québec, Canada; 2Laboratoire de Microbiologie et d’Immunologie,Faculté de Médecine Dentaire, Université de Montréal, C.P. 6128, Succursale Centre-ville, Montréal H3C 3J7, Québec, Canada; 3Groupe de Recherche en Biomécanique et Biomatériaux (GRBB), Département de Génie Biomédical, École Polytechnique de Montréal, C.P. 6079, Succursale Centre-ville, Montréal H3C 3A7, Québec, Canada; 4Laboratoire d’Électrostatique et de Matériaux Diélectriques, Centre Nationalde la Recherche Scientifique et Université Joseph Fourier, B.P. 166, 38042-Grenoble Cedex 9, France Abstract: Utilizing a plasma to achieve sterilization is a possible alternative to conventional sterilization means as far as sterilization of heat-sensitive materials and innocuity of sterilizing agents are concerned. A major issue of plasma sterilization is the respective roles of ultraviolet (UV)photons and reactive species such as atomic and molecular radicals. At reduced gas pressure (≤10 torr) and in mixtures containing oxygen, the UV photons dominate the inactivation process, with a significant contribution of oxygen atoms as an erosion agent. Actually, as erosion of the spore progresses, the number of UV photons successfully interacting with the genetic material increases. Thedifferent physicochemical processes at play during plasma sterilization are identified and analyzed, based on the specific characteristics of the spore survival curves. INTRODUCTION Sterilization is an act or process, physical or chemical, that destroys or eliminates all forms of life, especially microorganisms. Conventional sterilization techniques, such as those using autoclaves, ovens, and chemicalslike ethylene oxide (EtO), rely on irreversible metabolic inactivation or on breakdown of vital structural components of the microorganism. Plasma sterilization operates differently because of its specific active agents, which are ultraviolet (UV) photons and radicals (atoms or assembly of atoms with unpaired electrons, therefore chemically reactive, e.g., O and OH, respectively). An advantage ofthe plasma method is the possibility, under appropriate conditions, of achieving such a process at relatively low temperatures (≤50 °C), preserving the integrity of polymer-based instruments, which cannot be subjected to autoclaves and ovens [1,2]. Furthermore, plasma sterilization is safe, both for the operator and the patient, in contrast to EtO. The UV photons are expected to be more strongly(if not totally) reabsorbed by the ambient gas at atmospheric pressure than at reduced pressure (≤10 torr). This led us to consider two types of sterilizers: atmospheric- and reduced-pressure systems [1,2]. The respective roles of UV photons and radicals at reduced pressure are already well understood [1–4], which is not the case yet at atmospheric
presented at the 15thInternational Symposium on Plasma Chemistry, Orléans, France, 9–13 July 2001. Other presentations are presented in this issue, pp. 317–492. ‡Corresponding author
M. MOISAN et al.
pressure [5,6]. Our presentation focuses on reduced-pressure operation and is based on the analysis of the specific characteristics of the microorganism survival curves resulting from plasmasterilization. In both systems, the devices to be sterilized can be arranged to be either in contact with the discharge or with its flowing afterglow. Figure 1 shows a typical flowing-afterglow sterilizer.
Fig. 1 Flowing-afterglow 50-L sterilizer developed at Université de Montréal. It is supplied from a 2450-MHz surface-wave discharge operated at the 100–150 W power level in a 6 mm i.d. Pyrex tube....
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