Abstract: Atomic Spectroscopy Optical (atomic absorption spectroscopy, AAS; atomic emission spectroscopy, AES; atomic fluorescence spectroscopy, AFS; and optogalvanic spectroscopy) and mass spectrometric (magnetic sector, quadrupole mass analyzer, QMA; quadrupole ion trap, QIT; Fourier transform ion cyclotron resonance, FTICR; and time-of-flight, TOF) instrumentation are well suited for coupling to the glow discharge (GD). The GD is a relatively simple device. A potential gradient (500–1500 V) is applied between an anode and a cathode. In most cases, the sample is also the cathode. A noble gas (mostly Ar) is introduced into the discharge region before power initiation. When a potential is applied, electrons are accelerated toward the anode. As these electrons accelerate, they collide with gas atoms. A fraction of these collisions are of sufficient energy to remove an electron from a support gas atom, forming an ion. These ions are, in turn, accelerated toward the cathode. These ions impinge on the surface of the cathode, sputtering sample atoms from the surface. Sputtered atoms that do not redeposit on the surface diffuse into the excitation/ionization regions of the plasma where they can undergo excitation and/or ionization via a number of collisional processes, and the photons or ions created in this way can be detected with optical emission spectroscopy or mass spectrometry. GD sources offer a number of distinct advantages that make them well suited for specific types of analyses. These sources afford direct analysis of solid samples, thus minimizing the sample preparation required for analysis. The nature of the plasma also provides mutually exclusive atomization and excitation processes that help to minimize the matrix effects that plague so many other elemental techniques. In recent years, there is also increasing interest for using GD sources for liquid and gas analyses. In this article, first, the principles of operation of the GD plasma are reviewed, with an emphasis on how those principles relate to optical spectroscopy and mass spectrometry. Basic applications of the GD techniques are considered next. These include bulk analysis, surface analysis, and the analysis of solution and gaseous samples. The requirements necessary to obtain optical information are addressed following the analytical applications. This article focuses on the instrumentation needed to make optical measurements using the GD as an atomization/excitation source. Finally, mass spectrometric instrumentation and interfaces are addressed as they pertain to the use of a GD plasma as an ion source. GD sources provide analytically useful gas-phase species from solid samples. These sources can be interfaced with a variety of spectroscopic and spectrometric instruments for both quantitative and qualitative analyses.

Abstract: Purified water supply for human use, agriculture and industry is the major global priority nowadays. The advanced oxidation process based on atmospheric pressure non-thermal plasma (NTP) has been used for purification of wastewater, although the underlying mechanisms of degradation of organic pollutants are still unknown. In this study we employ two needle-type atmospheric pressure non-thermal plasma jets, i.e., indirect (ID-APPJ) and direct (D-APPJ) jets operating at Ar feed gas, for the treatment of methylene blue, methyl orange and congo red dyes, for two different times (i.e., 20 min and 30 min). Specifically, we study the decolorization/degradation of all three dyes using the above mentioned plasma sources, by means of UV-Vis spectroscopy, HPLC and a density meter. We also employ mass spectroscopy to verify whether only decolorization or also degradation takes place after treatment of the dyes by the NTP jets. Additionally, we analyze the interaction of OH radicals with all three dyes using reactive molecular dynamics simulations, based on the density functional-tight binding method. This investigation represents the first report on the degradation of these three different dyes by two types of NTP setups, analyzed by various methods, and based on both experimental and computational studies.

Abstract: We have computationally investigated the introduction of copper elemental particles in an inductively coupled plasma torch connected to a sampling cone, including for the first time the ionization of the sample. The sample is inserted as liquid particles, which are followed inside the entire torch, i.e., from the injector inlet up to the ionization and reaching the sampler. The spatial position of the ion clouds inside the torch as well as detailed information on the copper species fluxes at the position of the sampler orifice and the exhausts of the torch are provided. The effect of on- and off-axis injection is studied. We clearly show that the ion clouds of on-axis injected material are located closer to the sampler with less radial diffusion. This guarantees a higher transport efficiency through the sampler cone. Moreover, our model reveals the optimum ranges of applied power and flow rates, which ensure the proper position of ion clouds inside the torch, i.e., close enough to the sampler to increase the fraction that can enter the mass spectrometer and with minimum loss of material toward the exhausts as well as a sufficiently high plasma temperature for efficient ionization.

Abstract: Plasma catalysis is gaining increasing interest for various environmental applications, but the crucial question is whether plasma can be created inside catalyst pores and under which conditions. In practice, various catalytic support materials are used, with various dielectric constants. We investigate here the influence of the dielectric constant on the plasma properties inside catalyst pores and in the sheath in front of the pores, for various pore sizes. The calculations are performed by a two-dimensional fluid model for an atmospheric pressure dielectric barrier discharge in helium. The electron impact ionization rate, electron temperature, electron and ion density, as well as the potential distribution and surface charge density, are analyzed for a better understanding of the discharge behavior inside catalyst pores. The results indicate that, in a 100 μm pore, the electron impact ionization in the pore, which is characteristic for the plasma generation inside the pore, is greatly enhanced for dielectric constants below 300. Smaller pore sizes only yield enhanced ionization for smaller dielectric constants, i.e., up to εr = 200, 150, and 50 for pore sizes of 50, 30, and 10 μm. Thus, the most common catalyst supports, i.e., Al2O3 and SiO2, which have dielectric constants around εr = 8−11 and 4.2, respectively, should allow more easily that microdischarges can be formed inside catalyst pores, even for smaller pore sizes. On the other hand, ferroelectric materials with dielectric constants above 300 never seem to yield plasma enhancement inside catalyst pores, not even for 100 μm pore sizes. Furthermore, it is clear that the dielectric constant of the material has a large effect on the extent of plasma enhancement inside the catalyst pores, especially in the range between εr = 4 and εr = 200. The obtained results are explained in detail based on the surface charge density at the pore walls,
and the potential distribution and electron temperature inside and above the pores. The results obtained with this model are
important for plasma catalysis, as the production plasma species in catalyst pores might affect the catalyst properties, and thus
improve the applications of plasma catalysis.

Abstract: The hydrogenation of carbon dioxide in a dielectric barrier discharge plasma is studied with a one-dimensional fluid model. The spatially averaged densities of the most important end products formed in the CO2/H2 mixture are determined as a function of the initial gas mixing ratio. CO and H2O are found to be present at the highest densities and to a lower content also CH4, C2H6, CH2O, CH3OH, O2, and some other higher hydrocarbons and oxygenates. The main underlying reaction
pathways for the conversion of the inlet gases and the formation of CO, CH4, CH2O, and CH3OH are pointed out for various gas mixing ratios. The CO2 conversion and the production of value added products is found to be quite low, also in comparison to a CO2/CH4 mixture, and this can be explained by the model.

Abstract: In recent years there is increased interest in plasma-based CO2 conversion. Several plasma setups are being investigated for this purpose, but the most commonly used ones are a dielectric barrier discharge (DBD), a microwave (MW) plasma and a gliding arc (GA) reactor. In this proceedings paper, we will show results from our experiments in a (packed bed) DBD reactor and in a vortex-flow GA reactor, as well as from our model calculations for the detailed plasma chemistry in a DBD, MW and GA, for pure CO2 as well as mixtures of CO2 with N-2, CH4 and H2O.

Abstract: Pesticides are emerging contaminants frequently detected in the aquatic environment. In this work, a novel approach combining activated carbon adsorption, oxygen plasma treatment and ozonation was studied for the removal of the persistent chlorinated pesticide alachlor. A comparison was made between the removal efficiency and energy consumption for two different reactor operation modes: batchrecirculation and single-pass mode. The kinetics study revealed that the insufficient removal of alachlor by adsorption was significantly improved in terms of degradation efficiency and energy consumption when combined with the plasma treatment. The best efficiency (ca. 80% removal with an energy cost of 19.4 kWh mÀ3) was found for the single-pass operational mode of the reactor. In the batch-recirculating process, a complete elimination of alachlor by plasma treatment was observed after 30 min of treatment. Analysis of the reactive species induced by plasma in aqueous solutions showed that the decomposition of alachlor mainly occurred through a radical oxidation mechanism, with a minor contribution of long-living oxidants (O3, H2O2). Investigation of the alachlor oxidation pathways revealed six different oxidation mechanisms, including the loss of aromaticity which was never before reported for plasma-assisted degradation of aromatic pesticides. It was revealed that the removal rate and energy cost could be further improved with more than 50% by additional O3 gas bubbling in the solution reservoir.

Abstract: Cold physical plasma has limited tumor growth in many preclinical models and is, therefore, suggested as a putative therapeutic option against cancer. Yet, studies investigating the cells’ metastatic behavior following plasma treatment are scarce, although being of prime importance to evaluate the safety of this technology. Therefore, we investigated four human pancreatic cancer cell lines for their metastatic behavior in vitro and in chicken embryos (in ovo). Pancreatic cancer was chosen as it is particularly metastatic to the peritoneum and systemically, which is most predictive for outcome. In vitro, treatment with the kINPen plasma jet reduced pancreatic cancer cell activity and viability, along with unchanged or decreased motility. Additionally, the expression of adhesion markers relevant for metastasis was down-regulated, except for increased CD49d. Analysis of 3D tumor spheroid outgrowth showed a lack of plasma-spurred metastatic behavior. Finally, analysis of tumor tissue grown on chicken embryos validated the absence of an increase of metabolically active cells physically or chemically detached with plasma treatment. We conclude that plasma treatment is a safe and promising therapeutic option and that it does not promote metastatic behavior in pancreatic cancer cells in vitro and in ovo.

Abstract: Plasma catalysis is promising for various environmental, energy and chemical synthesis applications, but the underlying mechanisms are far from understood. Modeling can help to obtain a better insight in these mechanisms. Some burning questions relate to the plasma behavior inside packed bed reactors and whether plasma can penetrate into catalyst pores. In this paper, we try to provide answers to these questions, by means of both fluid modeling and particle-in-cell/Monte Carlo collision simulations. We present a short overview of recent findings obtained in our group by means of modeling, i.e., the enhanced electric field near the contact points and the streamer propagation through the packing in packed bed reactors, as well as the plasma behavior in catalyst pores, to determine the minimum pore size in which plasma streamers can penetrate.

Abstract: Physical plasmas generate unique mixes of reactive oxygen and nitrogen species (RONS or ROS). Only a bit more than a decade ago, these plasmas, operating at body temperature, started to be considered for medical therapy with considerably little mechanistic redox chemistry or biomedical research existing on that topic at that time. Today, a vast body of evidence is available on physical plasma-derived ROS, from their spatiotemporal resolution in the plasma gas phase to sophisticated chemical and biochemical analysis of these species once dissolved in liquids. Data from<italic>in silico</italic>analysis dissected potential reaction pathways of plasma-derived reactive species with biological membranes, and<italic>in vitro</italic>and<italic>in vivo</italic>experiments in cell and animal disease models identified molecular mechanisms and potential therapeutic benefits of physical plasmas. In 2013, the first medical plasma systems entered the European market as class IIa devices and have proven to be a valuable resource in dermatology, especially for supporting the healing of chronic wounds. The first results in cancer patients treated with plasma are promising, too. Due to the many potentials of this blooming new field ahead, there is a need to highlight the main concepts distilled from plasma research in chemistry and biology that serve as a mechanistic link between plasma physics (how and which plasma-derived ROS are produced) and therapy (what is the medical benefit). This inevitably puts cellular membranes in focus, as these are the natural interphase between ROS produced by plasmas and translation of their chemical reactivity into distinct biological responses.

Abstract: Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive cancers with a low response to treatment and a five-year survival rate below 5%. The ineffectiveness of treatment is partly because of an immunosuppressive tumor microenvironment, which comprises tumor-supportive pancreatic stellate cells (PSCs). Therefore, new therapeutic strategies are needed to tackle both the immunosuppressive PSC and pancreatic cancer cells (PCCs). Recently, physical cold atmospheric plasma consisting of reactive oxygen and nitrogen species has emerged as a novel treatment option for cancer. In this study, we investigated the cytotoxicity of plasma-treated phosphate-buffered saline (pPBS) using three PSC lines and four PCC lines and examined the immunogenicity of the induced cell death. We observed a decrease in the viability of PSC and PCC after pPBS treatment, with a higher efficacy in the latter. Two PCC lines expressed and released damage-associated molecular patterns characteristic of the induction of immunogenic cell death (ICD). In addition, pPBS-treated PCC were highly phagocytosed by dendritic cells (DCs), resulting in the maturation of DC. This indicates the high potential of pPBS to trigger ICD. In contrast, pPBS induced no ICD in PSC. In general, pPBS treatment of PCCs and PSCs created a more immunostimulatory secretion profile (higher TNF-α and IFN-γ, lower TGF-β) in coculture with DC. Altogether, these data show that plasma treatment via pPBS has the potential to induce ICD in PCCs and to reduce the immunosuppressive tumor microenvironment created by PSCs. Therefore, these data provide a strong experimental basis for further in vivo validation, which might potentially open the way for more successful combination strategies with immunotherapy for PDAC.

Abstract: We present an approach to incorporate the effect of vibrational nonequilibrium in molecular dynamics (MD) simulations. A perturbed canonical ensemble, in which selected modes are excited to higher temperature while all others remain equilibrated at low temperature, is simulated by applying a specifically tailored bias potential. Our method can be readily applied to any (classical or quantum mechanical) MD setup at virtually no additional computational cost and allows the study of reactions of vibrationally excited molecules in nonequilibrium environments such as plasmas. In combination with enhanced sampling methods, the vibrational efficacy and mode selectivity of vibrationally stimulated reactions can then be quantified in terms of chemically relevant observables, such as reaction rates and apparent free energy barriers. We first validate our method for the prototypical hydrogen exchange reaction and then show how it can capture the effect of vibrational excitation on a symmetric SN2 reaction and radical addition on CO2.

Abstract: Understanding the folding and stability of membrane proteins is of great importance in protein science. Recently, osmolytes and ionic liquids (ILs) are increasingly being used as drug delivery systems in the biopharmaceutical industry. However, the stability of membrane proteins in the presence of osmolytes and ILs is not yet fully understood. Besides, the effect of oxidative stress on membrane proteins with osmolytes or ILs has not been investigated. Therefore, we studied the influence of osmolytes and ILs as co-solvents on the stability of a model membrane protein (i.e., Bacteriorhodopsin in purple membrane of Halobacterium salinarum), using UV–Vis spectroscopy and molecular dynamics (MD) simulations. The MD simulations allowed us to determine the flexibility and solvent accessible surface area (SASA) of Bacteriorhodopsin protein in the presence and/or absence of cosolvents, as well as to carry out principal component analysis (PCA) to identify the most important movements in this protein. In addition, by means of UV–Vis spectroscopy we studied the effect of oxidative stress generated by cold atmospheric plasma on the stability of Bacteriorhodopsin in the presence and/or absence of co-solvents. This study is important for a better understanding of the stability of proteins in the presence of oxidative stress.

Abstract: Nitrogen oxyanions and oxyacids are important agents in atmospheric chemistry and medical biology. Although their chemical behavior in solution is relatively well understood, they may behave very differently at the water/air interface of atmospheric aerosols or at the membrane/water interface of cells. Here, we developed a fully classical model for molecular dynamics simulations of NO3−, NO2−, HNO3, and HNO2 in the framework of the GROMOS 53A6 and 54A7 force field versions. The model successfully accounted for the poorly structured solvation shell and ion pairing tendency of NO3−. Accurate pure-liquid properties and hydration free energies were obtained for the oxyacids. Simulations at the water/air interface showed a local enrichment of HNO3 and depletion of NO3−. The effect was discussed in light of earlier spectroscopic data and ab initio calculations, suggesting that HNO3 behaves as a weaker acid at the surface of water. Our model will hopefully allow for efficient and accurate simulations of nitrogen oxyanions and oxyacids in solution and at microheterogeneous interface environments.