Cold atmospheric-pressure plasmas are currently in use in medicine as surgical tools and are being evaluated for new applications, including wound treatment and cosmetic care. The disinfecting properties of plasmas are of particular interest, given the threat of antibiotic resistance to modern medicine. Plasma effluents comprise (V)UV photons and various reactive particles, such as accelerated ions and radicals, that modify biomolecules; however, a full understanding of the molecular mechanisms that underlie plasma-based disinfection has been lacking. Here, we investigate the antibacterial mechanisms of plasma, including the separate, additive and synergistic effects of plasma-generated (V)UV photons and particles at the cellular and molecular levels. Using scanning electron microscopy, we show that plasma-emitted particles cause physical damage to the cell envelope, whereas UV radiation does not. The lethal effects of the plasma effluent exceed the zone of physical damage. We demonstrate that both plasma-generated particles and (V)UV photons modify DNA nucleobases. The particles also induce breaks in the DNA backbone. The plasma effluent, and particularly the plasma-generated particles, also rapidly inactivate proteins in the cellular milieu. Thus, in addition to physical damage to the cellular envelope, modifications to DNA and proteins contribute to the bactericidal properties of cold atmospheric-pressure plasma.

Reactive plasmas are a well-known tool for material synthesis and surface modification. They offer a unique combination of non-equilibrium electron and ion driven plasma chemistry, energetic ions accelerated in the plasma sheath at the plasma–surface interface, high fluxes of reactive species towards surfaces and a friendly environment for thermolabile objects. Additionally, small negatively charged clusters can be generated, because they are confined in the positive plasma potential. Plasmas in hydrocarbon gases, and especially in acetylene, are a good example for the discussion of different plasma-chemical processes. These plasmas are involved in a plethora of possible applications ranging from fuel conversion to formation of single wall carbon nanotubes. This paper provides a concise overview of plasma-chemical reactions (PCRs) in low pressure reactive plasmas and discusses possible experimental and theoretical methods for the investigation of their plasma chemistry. An up-to-date summary of the knowledge about low pressure acetylene plasmas is given and two particular examples are discussed in detail: (a) Ar/C₂H₂ expanding thermal plasmas with electron temperatures below 0.3 eV and with a plasma chemistry initiated by charge transfer reactions and (b) radio frequency C₂H₂ plasmas, in which the energetic electrons mainly control PCRs.

A remote microscale atmospheric pressure plasma jet ( µ APPJ) with He, He/H ₂ O, He/O ₂ , and He/O ₂ /H ₂ O gas mixtures was used to study the transport of reactive species from the gas phase into the liquid and the following aqueous phase chemistry. The effects induced by the µ APPJ in water were quantitatively studied using phenol as a chemical probe and by measuring H ₂ O ₂ concentration and pH values. These results were combined with the analysis of the absolute densities of the reactive species and the modeling of convective/diffusion transport and recombination reactions in the effluent of the plasma jet. Additionally, modified plasma jets were used to show that the role of emitted photons in aqueous chemistry is negligible for these plasma sources. The fastest phenol degradation was measured for the He/O ₂ plasma, followed by He/H ₂ O, He/O ₂ /H ₂ O, and He plasmas. The modeled quantitative flux of O atoms into the liquid in the He/O ₂ plasma case was highly comparable with the phenol degradation rate and showed a very high transfer efficiency of reactive species from the plasma into the liquid, where more than half of the O atoms leaving the jet nozzle entered the liquid. The results indicate that the high oxidative effect of He/O ₂ plasma was primarily due to solvated O atoms, whereas OH radicals dominated the oxidative effects induced in water by plasmas with other gas mixtures. These findings help to understand, in a quantitative way, the complex interaction of cold atmospheric plasmas with aqueous solutions and will allow a better understanding of the interaction of these plasmas with water or buffered solutions containing biological macromolecules, microorganisms, or even eukaryotic cells. Additionally, the µ APPJ He/O ₂ plasma source seems to be an ideal tool for the generation of O atoms in aqueous solutions for any future studies of their reactivity.

An atmospheric pressure microplasma jet is developed for depositing homogeneous thin films from ${\mathrm{C}}_2{\mathrm{H}}_2$ . The adjustment of the gas flow through the microplasma jet assures optimal flow conditions as well as minimizes deposition inside the jet. In addition, the formation of an argon boundary layer surrounding the emerging plasma beam separates the ambient atmosphere from the flow of growth precursor. Thereby the incorporation of nitrogen and oxygen from the ambient atmosphere into the deposited film is suppressed. Soft polymerlike hydrogenated amorphous carbon $(a\text{-}\mathrm{C}:\mathrm{H})$ films are deposited at the rate of a few nm/s on the area of a few square millimeters.