Abstract
The mechanisms of sterilization and decontamination of surfaces are compared in direct and post discharge plasma treatments in two low-pressure reactors, microwave and inductively coupled plasma. It is shown that the removal of various biomolecules, such as proteins, pyrogens or peptides, can be obtained at high rates and low temperatures in the inductively coupled plasma (ICP) by using Ar/O2 mixtures. Similar efficiency is obtained for bacterial spores. Analysis of the discharge conditions illustrates the role of ion bombardment associated with O radicals, leading to a fast etching of organic matter. By contrast, the conditions obtained in the post discharge lead to much lower etching rates but also to a chemical modification of pyrogens, leading to their de-activation. The advantages of the two processes are discussed for the application to the practical case of decontamination of medical devices and reduction of hospital infections, illustrating the advantages and drawbacks of the two approaches.
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GENERAL SCIENTIFIC SUMMARY Introduction and background. Application of non-equilibrium plasma discharges for sterilization and decontamination of surfaces gains an increased attention since it offers highly effective, low-temperature process without need of toxic substances. However, in spite of numerous studies devoted to this topic, the knowledge regarding the underlying mechanisms of plasma action on biological systems remains still relatively poor, which is especially true in the cases of diverse biomolecules.
Main results. In order to gain a better insight into the processes occurring on the plasma-biological matter interfaces the plasma action on different biological samples was compared with the plasma properties determined by various diagnostics methods. Furthermore, two plasma sources differing in the position of the treated samples with respect to plasma were used: the samples were located either into the active plasma zone or to the near-post discharge. It is demonstrated that these two arrangements differ significantly not only in the rates at which different biomolecules are eliminated from the surfaces, but also in the nature of the processes leading to this effect: whereas in the first case the principal pathway of biomolecules removal appeared to be their chemical sputtering, chemical etching seems to be the dominating process in the near post-discharge.
Wider implications. The change of the main mechanism of elimination of biological residuals from surfaces reported in this study has important consequences in view of process optimization as well as its applicability in a real situation, since both pathways pose certain advantages and drawbacks as discussed in the article.