Plasma-induced Reactive Species Research Articles

D-Glucose Oxidation by Cold Atmospheric Plasma-Induced Reactive Species.

The glucose oxidation cascade is fascinating; although oxidation products have high economic value, they can manipulate the biological activity through posttranslational modification such as glycosylation of proteins, lipids, and nucleic acids. The concept of this work is based on the ability of reactive species induced by cold atmospheric plasma (CAP) in aqueous liquids and the corresponding gas–liquid interface to oxidize biomolecules under ambient conditions. Here, we report the oxidation of glucose by an argon-based dielectric barrier discharge plasma jet (kINPen) with a special emphasis on examining the reaction pathway to pinpoint the most prominent reactive species engaged in the observed oxidative transformation. Employing d-glucose and d-glucose-13C6 solutions and high-resolution mass spectrometry and ESI-tandem MS/MS spectrometry techniques, the occurrence of glucose oxidation products, for example, aldonic acids and aldaric acids, glucono- and glucaro-lactones, as well as less abundant sugar acids including ribonic acid, arabinuronic acid, oxoadipic acid, 3-deoxy-ribose, glutaconic acid, and glucic acid were surveyed. The findings provide deep insights into CAP chemistry, reflecting a switch of reactive species generation with the feed gas modulation (Ar or Ar/O2 with N2 curtain gas). Depending on the gas phase composition, a combination of oxygen-derived short-lived hydroxyl (•OH)/atomic oxygen [O(3P)] radicals was found responsible for the glucose oxidation cascade. The results further illustrate that the presence of carbohydrates in cell culture media, gel formulations (agar), or other liquid targets (juices) modulate the availability of CAP-generated species in vitro. In addition, a glycocalyx is attached to many mammalian proteins, which is essential for the respective physiologic role. It might be questioned if its oxidation plays a role in CAP activity.

Influence of plasma oxidation on proteins: modeling at the molecular level

Recently, the use of cold atmospheric plasmas for cancer therapy has become one of the most exciting topics of plasma application. Despite promising results from a large number of studies, the underlying mechanisms by which plasma acts on cancer cells are still elusive and require more thorough fundamental investigations. In this account, an overview is provided on our latest computational studies performed to investigate the interaction mechanisms of reactive oxygen and nitrogen species generated by cold atmospheric plasma with specific proteins relevant for cancer (treatment). In particular, the main attention is paid on the effect of these plasma species on the permeability of aquaporin and cystine/glutamate transporter xCT, used as model systems for integral membrane proteins. The simulation results help to gain insight in the underlying mechanisms of the noticeable rise of plasma-induced reactive species observed in cancer cells compared to normal cells, thereby improving overall understanding on the role of integral membrane proteins in the selective anticancer capacity of cold atmospheric plasma.

Modeling of an atmospheric pressure plasma-liquid anodic interface: Solvated electrons and silver reduction

Solvated electrons (eaq−) generated by atmospheric pressure plasmas in contact with liquids are a key source of plasma-induced liquid chemistry that enable applications in biotechnology and nanoparticle synthesis. In this paper, we report liquid phase reactive species concentrations near an anodic plasma-liquid interface as described by a fluid model. In particular, the interfacial structures and plasma-induced reactive species in NaCl and AgNO3 solutions as generated by a pulsed plasma are highlighted. The results show that the magnitude and the penetration depth of the eaq− concentration in AgNO3 solution are smaller than that in the NaCl solution due to the scavenger reactions of eaq− by Ag+ and NO3−. The early products of the plasma-induced Ag+ reduction are also presented, and the impact of the current density, the pulse width, and the AgNO3 concentration on the silver reduction is analyzed. It is further shown that a typical OH radical flux present in such plasmas can highly impact the eaq− concentration and the Ag+ reduction while the impact of vacuum ultraviolet radiation, H, and H2O2 is less pronounced.

Reactive oxygen and nitrogen species in Ar + N2 + O2 atmospheric-pressure nanosecond pulsed plasmas in contact with liquid

In this paper, a nanosecond pulse gas-liquid discharge is generated in Ar and Ar with admixtures of N2 or O2. The discharge images and waveforms of pulse voltage and discharge current are used to characterize gas-liquid discharge characteristics; optical emission spectroscopy and Fourier-transform infrared spectroscopy are employed to diagnose the reactive species in the gas phase, and chemical probe methods are employed to investigate plasma-induced reactive species (H2O2, NO2−, and NO3−) in the liquid phase. The effects of added contents of N2 or O2 in Ar discharge on the formation of reactive species are investigated. It is found that the productions of gaseous O and O3 increase obviously with the increasing O2 ratio and the productions of gaseous N2 (C-B), NO, NO2, and N2O increase with the increasing N2 ratio. Additionally, for the reactive species measured in the liquid phase, the increase in the N2 ratio in Ar discharge is beneficial for increasing the concentrations of NO3− and NO2− and decreasing the concentrations of H2O2, while the increase in the O2 ratio in Ar discharge decreases the concentrations of H2O2 and inhibits the production of NO2−.

Degradation and mineralization of ciprofloxacin by gas–liquid discharge non-thermal plasma

A typical quinolones antibiotic ciprofloxacin (CIP) in aqueous solution was degraded by a gas–liquid discharge non-thermal plasma system. The discharge plasma power and the emission intensity of the excited reactive species (RS) generated in the gas phase were detected by the oscilloscope and the optical emission spectroscopy. The effects of various parameters on CIP degradation, i.e. input powers, initial concentrations addition of radical scavengers and pH values were investigated. With the increase of discharge power, the degradation efficiency increased but the energy efficiency significantly reduced. The degradation efficiency also reduced under high concentration of initial CIP conditions due to the competitive reactions between the plasma-induced RS with the degradation intermediates of CIP. Different radical scavengers (isopropanol and CCl4) on ·OH and H· were added into the reaction system and the oxidation effects of ·OH radicals have been proved with high degradation capacity on CIP. Moreover, the long-term degradation effect on CIP in the plasma-treated aqueous solution proved that the long-lived RS (H2O2 and O3, etc) might play key roles on the stay effect through multiple aqueous reactions leading to production of ·OH. The degradation intermediates were determined by the method of electrospray ionization (+)-mass spectroscopy, and the possible degradation mechanism were presented.

Total yield of reactive species originating from an atmospheric pressure plasma jet in real time.

It is now well established that plasma-induced reactive species are key agents involved in many biochemical reactions. This work reports on the formation of plasma reactive species in an acidified ferrous sulfate (Fricke) solution interacting with an atmospheric pressure plasma jet (APPJ). A yield of ferric (Fe3+) ions measured using in situ absorption spectroscopy was attributed to the formation of plasma reactive species provided and/or originated in the solution. The results indicated that the number of reactive species formed was proportional to plasma frequency and voltage. However, the Fe3+ yield per pulse decreased with increased frequency. To obtain a better understanding of the processes and species involved in the chemical reactions due to plasma exposure, Fe3+ yields were calculated and compared to the experimental data. At higher frequencies, there was insufficient time to complete all the reactions before the next pulse reached the solution; at lower frequencies, the Fe3+ yield was higher because of the relatively longer time available for reactions to occur. In addition, the comparison between DNA damage levels and Fe3+ yields was investigated under different experimental conditions in order to verify the usefulness of both the Fricke solution and the DNA molecule as a probe to characterize APPJs.

Immunogenic Cell Death In Murine Colon-Carcinoma Cells Following Exposure To Cold Physical Plasma-Treated Saline Solution

Diffuse peritoneal metastasis of gastrointestinal tumors is a life-threatening complication in end-stage tumor patients. Standard of care is hyperthermic intraperitoneal chemotherapy (HIPEC) and/or radiation therapy, both associated with significant side effects [1]. Previous studies have suggested that cold physical plasma may present a new anti-tumor tool with few to none side effects [2]. Moreover, plasma-induced reactive species can be transferred to cell culture medium where they react to more stable entities. We were able to demonstrate that phosphate-buffered saline (PBS) treated with cold physical plasma has toxic effects on mouse carcinoma cells cultured in 2D. We observed a reduced metabolic activities and apoptotic cell death. Morphological alterations, such as spiking of nuclei and changes in the shape of cytofilaments were also visible. Accordingly, treatment increased cell stiffness and reduced cell motility. Cancer cells are able to develop several mechanisms to subvert and avoid immune response. Danger associated molecular patterns (DAMPs) are linked to an immunogenic cell death (ICD) [3]. We observed an upregulation of DAMPs on the cell surface as well as increased concentrations in the cell’s liquid surroundings following incubation with plasma-treated saline. The activation of the immune system for cancer therapy is a promising approach. Animal experiments will show whether plasma-treated saline solution is effective in vivo and could be in principle considered for medical application.

Decomposition of Aqueous Anatoxin-a Using Underwater Dielectric Barrier Discharge Plasma Created in a Porous Ceramic Tube

This work investigated the decomposition of aqueous anatoxin-a originated from cyanobacteria using an underwater dielectric barrier discharge plasma system based on a porous ceramic tube and an alternating current (AC) high voltage. Plasmatic gas generated inside the porous ceramic tube was uniformly dispersed in the form of numerous bubbles into the aqueous solution through the micro-pores of the ceramic tube, which allowed an effective contact between the plasmatic gas and the aqueous anatoxin-a solution. Effect of applied voltage, treatment time and the coexistence of nutrients such as , and glucose on the decomposition of anatoxin-a was examined. Chemical analyses of the plasma-treated anatoxin-a solution using liquid chromatography-mass spectrometry (LC-MS) and ion chromatography (IC) were performed to elucidate the mineralization mechanisms. Increasing the voltage improved the anatoxin-a decomposition efficiency due to the increased discharge power, but the energy required to remove a given amount of anatoxin-a was similar, regardless of the voltage. At an applied voltage of 17.2 kV (oxygen flow rate: ), anatoxin-a at an initial concentration of (volume: 0.5 L) was successfully treated within 3 min. The chemical analyses using LC-MS and IC suggested that the intermediates with molecular weights of 123~161 produced by the attack of plasma-induced reactive species on anatoxin-a molecule were further oxidized to stable compounds such as acetic acid, formic acid and oxalic acid.

Cytotoxic macrophage-released tumour necrosis factor-alpha (TNF-α) as a killing mechanism for cancer cell death after cold plasma activation

The present study aims at studying the anticancer role of cold plasma-activated immune cells. The direct anti-cancer activity of plasma-activated immune cells against human solid cancers has not been described so far. Hence, we assessed the effect of plasma-treated RAW264.7 macrophages on cancer cell growth after co-culture. In particular, flow cytometer analysis revealed that plasma did not induce any cell death in RAW264.7 macrophages. Interestingly, immunofluorescence and western blot analysis confirmed that TNF-α released from plasma-activated macrophages acts as a tumour cell death inducer. In support of these findings, activated macrophages down-regulated the cell growth in solid cancer cell lines and induced cell death in vitro. Together our findings suggest plasma-induced reactive species recruit cytotoxic macrophages to release TNF-α, which blocks cancer cell growth and can have the potential to contribute to reducing tumour growth in vivo in the near future.

Dielectric barrier discharge plasma used as a means for the remediation of soils contaminated by non-aqueous phase liquids

A plane-to-grid dielectric barrier discharge (DBD) reactor operating with air at atmospheric pressure was used to investigate the removal of non-aqueous phase liquids (NAPLs) from soil layers. A mixture of n-C10, n-C12 and n-C16 was used as a model NAPL that polluted the soil at a very high initial concentration (100,000mg/kg-soil). The effect of treatment time, energy consumption, and soil thickness on the NAPL removal efficiency was investigated, the plasma active species were identified, and the macroscopic gas temperature was determined. The NAPL remediation efficiency found to be as high as 99.9% after 60–120s of plasma treatment, depending on soil thickness. The energy density required to remediate completely the NAPL was about 600J/g-soil and was practically independent of the soil thickness, indicating that the DBD-based plasma has the potential to become a highly cost-effective technology for the remediation of NAPL-contaminated soils. N2+, N2∗, NOx and O3 were identified as plasma-induced reactive species, a maximum gas temperature close to 300°C was recorded, and the total carbon detected in exhaust gases, in the form of CO and CO2, was ca 40% of that contained in the NAPL removed from the soil. The main mechanisms of NAPL removal by plasma found to be the evaporation of organic compounds coupled with their oxidation in liquid and gas phase. Using ATR-FTIR in combination with high-throughput organic profiling analysis by GC–MS, ketones and alcohols were identified as the main intermediate products of alkanes oxidation in soil matrix.