The gliding arc discharge plasma reactors are known as a source of non-equilibrium plasma at atmospheric pressure. In the present study, generation of dominant reactive oxygen and nitrogen species in gaseous and liquid phase in water by the compact gliding arc device (mini-GAD) and corresponding bactericidal effects were investigated. Water and phosphate buffer solutions were used as model liquids. Mini-GAD is a strong source of nitrogen oxides (up to 800 ppm NO and 200 ppm NO₂) that result in high concentrations of nitrites and nitrates in water solutions. The highest bactericidal efficacy towards Escherichia coli was achieved for non-buffered water solution.

Pulsed corona discharges propagated in argon (or in argon with added water vapor) at atmospheric pressure on the interior surface of a 49 cm long quartz tube were investigated for the application of surface bio-decontamination. H₂O molecule dissociation in the argon plasma generated reactive species (i.e. OH in ground and excited states) and UV emission, which both directly affected bacterial cells. In order to facilitate the evaluation of the contribution of UV radiation, a DNA damage repair defective bacterial strain, Escherichia coli DH-1, was used. Discharge characteristics, including propagation velocity and plasma temperature, were measured. Up to ~5.5 and ~5 log₁₀ reductions were observed for E. coli DH-1 bacteria (from 10⁶ initial load) exposed 2 cm and 44 cm away from the charged electrode, respectively, for a 20 min plasma treatment. The factors contributing to the observed bactericidal effect include desiccation, reactive oxygen species (OH) plus H₂O₂ accumulation in the liquid phase, and UV-B (and possibly VUV) emission in dry argon. The steady state temperature measured on the quartz tube wall did not exceeded 29 °C; the contribution of heating, along with that of H₂O₂ accumulation, was estimated to be low. The effect of UV-B emission alone or in combination with the other stress factors of the plasma process was examined for different operating conditions.

In the technological processes requiring mild treatment, such as soft materials processing or medical applications, an important role is played by non-equilibrium plasma reactors with dielectric barrier discharge (DBD), that when generated in noble gases allows for the effective treatment of biological material at a low temperature. The aim of this study is to determine the operating parameters of an atmospheric pressure, radio-frequency DBD plasma jet reactor for the precise treatment of biological materials. The tested parameters were the shape of the discharge (its length and volume), current and voltage signals, as well as the power consumed by the reactor for various composition and flow rates of the working gas. To determine the applicability in medicine, the temperature, pH, concentrations of H₂O₂, NO₂⁻ and NO₃⁻ and Escherichia coli log reduction in the plasma treated liquids were determined. The obtained results show that for certain operating parameters, a narrow shape of plasma stream can generate significant amounts of H₂O₂, allowing for the mild decontamination of bacteria at a relatively low power of the system, safe for the treatment of biological materials.

We studied the chemical and bactericidal properties of plasma-modified amino acid leucine (Leu) treated in phosphate-buffered saline (PBS) using an atmospheric-pressure plasma jet operating with He/O ₂ gas. We determined the initial formation of hypochlorite by the reaction of plasma-supplied O atoms with chloride ions in PBS, followed by the subsequent chlorination of Leu. The principal chemical process involved the formation of Leu monochloramine and Leu dichloramine. The products of plasma-modified Leu further possessed post-discharge reactivity characterized by the decay of Leu chloramines to the secondary products, i.e. isovaleraldehyde, isovaleronitrile, and N-chloromethyl-3-butaldimine. Our study of the effects of Leu on the viability of Escherichia coli bacteria in the plasma-treated PBS solution demonstrated time-and pH-dependent cytotoxic behavior, which were associated with the formation of different reaction products. At shorter treatment times, the addition of Leu hindered the bactericidal properties of plasma-treated PBS caused by the consumption of bactericidal hypochlorite in reaction with Leu and formation of non-bactericidal Leu monochloramine. Acidification to pH = 3 and longer plasma treatment substantially enhanced the bactericidal effects of Leu solutions, which were tentatively assigned to the formation of Leu dichloramine.