Nonthermal decontamination of biological media by atmospheric-pressure plasmas: review, analysis, and prospects

Although the use of an electrical discharge to disinfect water was suggested and applied more than a hundred years ago, basic and applied research on the interaction of plasmas with biological media was extensively carried out only relatively recently. In this context, a review of various works on the germicidal effects of atmospheric pressure, "cold" plasmas, is presented. The nonequilibrium discharge devices discussed in this review, which have been used in biological applications by various investigators, are the corona discharge, the diffuse dielectric-barrier discharge, the resistive barrier discharge, and the atmospheric-pressure plasma jet. Analysis of the inactivation kinetics for various bacteria seeded in (or on) various media and exposed to the plasma generated by these devices, showed that three types of survivor curves exist, depending on the type of micro-organism, the type of medium, and the type of exposure (direct versus remote). Insights into the roles of UV radiation, active species, and charged particles has led to the conclusion that chemically reactive species, such as free radicals, play the most important role in the inactivation process. In addition, recent results suggesting that biomanipulation of the cells of micro-organisms with nonequilibrium plasmas is possible are highlighted.