Plasma technical and microbiological characterization of newly developed VHF plasmas

Zur Sterilisation medizinischer Instrumente wird ein kapazitiv gekoppeltes Niederdruckplasma (VHF-CCP) entwickelt und mit optischer Emissionsspektroskopie, Multipolresonanzsonde und Langmuir Sonde charakterisiert. Mittels CCD-Kamera und ortsaufgelösten Sondenmessungen wird die Homogenität der Entladung untersucht und ein homogener Bereich für die Sterilisation definiert. Sterilisationsversuche mit Testkeimen bestätigen die Sterilisationsleistung des VHF-CCP. Zur Untersuchung der Sterilisationsmechanismen werden sowohl Plasma als auch Bakterien in Einzelbestandteilen untersucht. Hierfür wird ein alternativer UV+Hitze-Aufbau verwendet, der es ermöglicht UV-Strahlung und Hitze des Plasmas nachzubilden. Bio-Makromoleküle werden ausgewählt, um den Einfluss von Plasma auf einzelne Zellbestandteile zu untersuchen. Hierbei liegt der Fokus auf Proteinen und DNA. Aus den gewonnenen Erkenntnissen wird ein Desktopsterilisator zur Sterilisation medizinischer Instrumente entwickelt.A capacitively coupled low-pressure plasma (VHF-CCP) is developed for the sterilization of medical instruments and characterized by means of optical emission spectroscopy, multipole resonance probe and Langmuir probe diagnostics. Homogeneity of the discharge is investigated with a CCD camera and space-resolved probe measurements. A homogeneous area for sterilization is defined. Sterilization tests confirm sterilization efficacy of the VHF-CCP. In order to unravel sterilization mechanisms, single components of plasma as well as of bacteria are investigated. Therefore, an alternative UV+heat-setup is employed, enabling to re-enact UV radiation and heat of the plasma. Bio-macromolecules are selected to investigate the impact of plasma on single cell components. Here, the focus is on proteins and DNA. From the results obtained, a desktop sterilizer for the sterilization of medical instruments is developed

Characterisation of volume and surface dielectric barrier discharges in N2_2–O2_2 mixtures using optical emission spectroscopy

A volume and a twin surface dielectric barrier discharge (VDBD and SDBD) are generated in different nitrogen–oxygen mixtures at atmospheric pressure by applying damped sinusoidal voltage waveforms with oscillation periods in the microsecond time scale. Both electrode configurations are located inside vacuum vessels and operated in a controlled atmosphere to exclude the influence of surrounding air. The discharges are characterised with different spatial and temporal resolution by applying absolutely calibrated optical emission spectroscopy in conjunction with numerical simulations and current–voltage measurements. Plasma parameters, namely the electron density and the reduced electric field, and the dissipated power are found to depend strongly on the oxygen content in the working gas mixture. Different spatial and temporal distributions of plasma parameters and dissipated power are explained by surface and residual volume charges for different O$_2$ admixtures due to their effects on the electron recombination rate. Thus, the oxygen admixture is found to strongly influence the breakdown process and plasma conditions of a VDBD and a SDBD

Study on chemical modifications of glutathione by cold atmospheric pressure plasma (Cap) operated in air in the presence of Fe(II) and Fe(III) complexes

Cold atmospheric pressure plasma is an attractive new research area in clinical trials to treat skin diseases. However, the principles of plasma modification of biomolecules in aqueous solutions remain elusive. It is intriguing how reactive oxygen and nitrogen species (RONS) produced by plasma interact on a molecular level in a biological environment. Previously, we identified the chemical effects of dielectric barrier discharges (DBD) on the glutathione (GSH) and glutathione disulphide (GSSG) molecules as the most important redox pair in organisms responsible for detoxification of intracellular reactive species. However, in the human body there are also present redox-active metals such as iron, which is the most abundant transition metal in healthy humans. In the present study, the time-dependent chemical modifications on GSH and GSSG in the presence of iron(II) and iron(III) complexes caused by a dielectric barrier discharge (DBD) under ambient conditions were investigated by IR spectroscopy, mass spectrometry and High Performance Liquid Chromatography (HPLC). HPLC chromatograms revealed one clean peak after treatment of both GSH and GSSH with the dielectric barrier discharge (DBD) plasma, which corresponded to glutathione sulfonic acid GSO$_3$H. The ESI-MS measurements confirmed the presence of glutathione sulfonic acid. In our experiments, involving either iron(II) or iron(III) complexes, glutathione sulfonic acid GSO$_3$H appeared as the main oxidation product. This is in sharp contrast to GSH/GSSG treatment with DBD plasma in the absence of metal ions, which gave a wild mixture of products. Also interesting, no nitrosylation of GSH/GSSG was oberved in the presence of iron complexes, which seems to indicate a preferential oxygen activation chemistry by this transition metal ion

The role of humidity and UV-C emission in the inactivation of B. subtilis\textit {B. subtilis} spores during atmospheric-pressure dielectric barrier discharge treatment

Experiments are performed to assess the inactivation of $\textit {Bacillus subtilis}$ spores using a non-thermal atmospheric-pressure dielectric barrier discharge. The plasma source used in this study is mounted inside a vacuum vessel and operated in controlled gas mixtures. In this context, spore inactivation is measured under varying nitrogen/oxygen and humidity content and compared to spore inactivation using ambient air. Operating the dielectric barrier discharge in a sealed vessel offers the ability to distinguish between possible spore inactivation mechanisms since different process gas mixtures lead to the formation of distinct reactive species. The UV irradiance and the ozone density within the plasma volume are determined applying spectroscopic diagnostics with neither found to fully correlate with spore inactivation. It is found that spore inactivation is most strongly correlated with the humidity content in the feed gas, implying that reactive species formed, either directly or indirectly, from water molecules are strong mediators of spore inactivation