Low-temperature Atmospheric Pressure Plasmas Research Articles

Plasma-surface-modified SnO2–CuCl nanocomposite for highly selective electrocatalytic CO2 conversion

Conversion of CO2 into useful chemicals via electrochemical methods is a promising approach for mitigating global CO2 emissions and transiting towards green chemical production. In this work, a tin oxide-copper chloride (SnO2–CuCl) nanocomposite catalyst for efficient CO2 conversion is developed using low-temperature atmospheric-pressure plasmas. The SnO2–CuCl catalyst which acquired a unique structure subjected to the dielectric barrier discharge (DBD) plasma (SnO2–CuCl-DBD), effectively inhibits the hydrogen evolution reaction (HER) in the electrocatalytic process. Compared with the untreated SnO2–CuCl sample, the H2 generation efficiency of the SnO2–CuCl-DBD electrocatalyst decreased from 9.79 to 3.41 %. The demonstrated efficiency of SnO2–CuCl-DBD catalyst for conversion of CO2 to C1 products (formate and CO) is 94.37 % at 1.8 V (vs Ag/AgCl), which is very competitive to the reported state-of-the-art catalyst. The outcomes of this research provide a new practical surface science approach for engineering advanced electrocatalysts for effective conversion of CO2 into value-added chemical products.

Potential formation on floating metal plate treated by low-temperature atmospheric pressure plasma jet

In the biomedical applications using low-temperature atmospheric pressure plasmas, charging on surface of the targets could play an important role. In this study, we have investigated potential formed on an electrically floating copper plate treated by a low-temperature atmospheric pressure helium plasma jet. The potential of the copper plate was measured by an electrostatic sensor in a non-contact manner. It was found that the potential on the copper plate could be controlled from 200 to −600 V by changing the distance between the nozzle of plasma device and the surface of copper plate. We discussed the charging mechanism such as collection of charged particles and several processes of electron emission including thermionic, field emission, secondary electron emission, and photoelectric processes.

Detecting Trace Gases at PPM Levels with Low Temperature Plasma Optical Emission Spectroscopy

Detecting Trace Gases at PPM Levels with Low Temperature Plasma Optical Emission Spectroscopy

Detecting Trace Gases at Ppm Levels with Low Temperature Plasma Optical Emission Spectroscopy

The detection of trace levels of molecular gases has gained increasing attention in many fields from atmospheric pollution and climate change monitoring to industrial safety and breath analysis for clinical diagnosis. Established techniques e.g. mass spectrometry, gas chromatography, electrochemical offer accuracy but are bulky and expensive. Apart from improving limits of detection (LOD) and increasing the number of target species, there is a major drive towards system miniaturisation and cost reduction in order to enhance field deployment e.g. for rapid continuous environmental monitoring via autonomous distributed networks or point of care clinical breath screening. Tuneable diode laser IR absorption spectroscopy (TLDAS) and atomic emission spectroscopy ICP-AES are routine laboratory spectroscopic techniques where future miniaturisation research includes, for example, microwave, photoacoustic-MEMS, broadband tuneable quantum cascade lasers or supercontinuum IR lasers, high sensitivity nanomaterials, among others. The advent of non-equilibrium low-temperature (NELT) atmospheric pressure plasmas opens up the possibility of using plasma optical emission spectroscopy (OES) for portable and/or low-cost detection in a diverse range of applications. However the poor quality of the spectra from these plasmas requires additional machine learning techniques to develop accurate models based on optical emission training samples. Our original work involving unsupervised principal component analysis indicated significant cluster separation even at sub-ppm levels of e.g. NO impurity gases. Recently we have investigated supervised learning using Partial Least Squares Discriminant Analysis (PLS-DA) using a dataset of He-CH4 spectra where the CH4 concentration varies from 0 – 100 ppm. Methane is a important hydrocarbon gas found in a number of fields from breath analysis to natural gas production and research is ongoing into accurate environmental CH4 detectors in the ppm range.The spectra were obtained from a small RF capillary plasma, 0.7mm in diameter and 5mm long. Spectra were obtained using a Ocean Optics HR4000CG-UV-NIR spectrometer in the wavelength range 194 – 1122 nm (interval 0.25 nm) Data is collected across 3648 variables (wavelengths) with up to 720 samples per dataset, and up to 9 CH4 concentration categories (0 to 100 ppm). Spectral features corresponding to He, hydrogen, carbon-related and impurities (N2, O2, OH/H2O) were observed. No peak can be assigned unambiguously to any particular species. The dominant peaks for 100% He (587.95nm, 707.08nm) varied by ~26% (std. dev). On introduction of CH4, their intensity remained constant (within 1 std. dev) up to ~23 ppm, falling thereafter. In these small atmospheric plasmas, the gas temperature remains cold and hydrocarbon fragmentation is thought to be minimal. Minor peaks indicative of possible CH and C2 fragments were observed but mainly at the higher concentrations. Atomic hydrogen is a possible CH4 fragment, although a contribution from H2O impurity fragmentation is also likely. The other impurity peaks, although of low intensity, have been found to play an important role in algorithm recognition.Predictive models were generated using PLS-DA with two general approaches explored, namely (i) 2-class and (ii) 8-class. In the former, for a threshold of 2 ppm CH4, the model accuracy was > 95% with < 10 latent variables (LV). In the 8-class model, the initial accuracy struggled to reach 60%, despite a range of standard pre-processing approaches employed. Our OES spectra represent high dimensionality collinear data with inherent pattern variability, temporal drift and low resolution as a penalty for the simple low-cost construction. This presents a serious challenge to developing robust machine learning algorithms. Variable Importance in Projection (VIP) outputs the relative significance of each wavelength variable to model’s predictive accuracy and provides insight into how algorithms function and their sensitivity to OES features and plasma chemistry. Using VIP-informed wavelength feature selection and peak modification we obtain high predictive accuracy (>90%) for separate training and test session data with a LOD of 1 ppm. Analysis shows that of the 12 most significant peaks, 6 are due to impurity transitions while the three possible CH4 fragment related transitions are noticeable only at high CH4 concentration. While high temperature plasma techniques (e.g. ICP) rely on molecular fragmentation, this is unlikely to occur in NELT plasmas due to the low energy density. We believe instead, the introduction of the target molecule into the plasma impacts on the low energy side of the electron energy distribution function, affecting electron density and temperature, which in turn is visible in the excitation and vibrational/rotational transitions of carrier and impurity gases. The development of more sophisticated machine learning algorithms capable of handling spectral data from greater complexity target mixtures will provide both an insight into and progress in tandem with improved understanding of NELT plasma physics and chemistry parameters. Figure 1

Effects of Low Temperature Plasmas on Proteins

When operated in an environment containing oxygen and nitrogen low temperature atmospheric pressure plasmas generate copious amounts of reactive oxygen species and reactive nitrogen species. These species can be transported to react with biological matter and induce cellular effects ranging from inactivation to proliferation, depending on the operating conditions. Although much work has been done on the cellular level (prokaryotes and eukaryotes), very little and mostly preliminary experiments were carried out on biomolecules, such as proteins. Proteins, which are chains of amino acids, are involved in almost all cellular functions. Therefore it is crucial to elucidate the effect of plasma on proteins and their structures. Here, some of the few investigations done on this subject are briefly reviewed. Only few select proteins have been investigated so far and the understanding of the biochemistry induced by plasma on the molecular level remains quite limited.

A numerical simulation study on active species production in dense methane-air plasma discharge

Recently, low-temperature atmospheric pressure plasmas have been proposed as a potential type of ‘reaction carrier’ for the conversion of methane into value-added chemicals. In this paper, the multi-physics field coupling software of COMSOL is used to simulate the detailed discharge characteristics of atmospheric pressure methane-air plasma. A two-dimensional axisymmetric fluid model is constructed, in which 77 plasma chemical reactions and 32 different species are taken into account. The spatial density distributions of dominant charged ions and reactive radical species, such as H, O, CH3, and CH2, are presented, which is due to plasma chemical reactions of methane/air dissociation (or ionization) and reforming of small fragment radical species. The physicochemical mechanisms of methane dissociation and radical species recombination are also discussed and analyzed.

Measurements of Plasma-Generated Hydroxyl and Hydrogen Peroxide Concentrations for Plasma Medicine Applications

Low-temperature, atmospheric pressure plasmas (LTPs) produce reactive oxygen and nitrogen species [O, O2−, O2 ( $^{1}\Delta $ ), hydroxyl (OH), H2O2, NO, NO2 $\ldots $ ]. In biological and medical applications, the concentrations and fluxes of these species play a crucial role in the biological outcomes. Many of these species are produced in the gaseous phase and at the gas-liquid interface when LTP is applied to biological media. In the medium, the plasma-produced oxygen reactive species and nitrogen reactive species generate long-lived species, such as hydrogen peroxide (H2O2), nitrites (NO2−), nitrates (NO3−), and organic peroxides (RO2). In particular, hydrogen peroxide is known to cause various oxidizing reactions in biological cells. One of the pathways to the creation of hydrogen peroxide is the reaction between OH radicals. Therefore, the measurement of OH concentration is of great importance. In this paper, we report on the measurements of OH in the gas-liquid interface using laser-induced fluorescence and measurements of H2O2 concentration in biological media. In addition, the effects of plasma activated media on cancer cells are briefly discussed.

Reactions of nitroxide radicals in aqueous solutions exposed to non-thermal plasma: limitations of spin trapping of the plasma induced species

Low temperature (‘cold’) atmospheric pressure plasmas have gained much attention in recent years due to their biomedical effects achieved through the interactions of plasma-induced species with the biological substrate. Monitoring of the radical species in an aqueous biological milieu is usually performed via electron paramagnetic resonance (EPR) spectroscopy using various nitrone spin traps, which form persistent radical adducts with the short-lived radicals. However, the stability of these nitroxide radical adducts in the plasma-specific environment is not well known. In this work, chemical transformations of nitroxide radicals in aqueous solutions using a model nitroxide 4-oxo-TEMPO were studied using EPR and LC-MS. The kinetics of the nitroxide decay when the solution was exposed to plasma were assessed, and the reactive pathways proposed. The use of different scavengers enabled identification of the types of reactive species which cause the decay, indicating the predominant nitroxide group reduction in oxygen-free plasmas. The 2H adduct of the PBN spin trap (PBN-D) was shown to decay similarly to the model molecule 4-oxo-TEMPO. The decay of the spin adducts in plasma-treated solutions must be considered to avoid rendering the spin trapping results unreliable. In particular, the selectivity of the decay indicated the limitations of the PTIO/PTI nitroxide system in the detection of nitric oxide.

Low-temperature plasma treatment induces DNA damage leading to necrotic cell death in primary prostate epithelial cells

Background:In recent years, the rapidly advancing field of low-temperature atmospheric pressure plasmas has shown considerable promise for future translational biomedical applications, including cancer therapy, through the generation of reactive oxygen and nitrogen species.Method:The cytopathic effect of low-temperature plasma was first verified in two commonly used prostate cell lines: BPH-1 and PC-3 cells. The study was then extended to analyse the effects in paired normal and tumour (Gleason grade 7) prostate epithelial cells cultured directly from patient tissue. Hydrogen peroxide (H2O2) and staurosporine were used as controls throughout.Results:Low-temperature plasma (LTP) exposure resulted in high levels of DNA damage, a reduction in cell viability, and colony-forming ability. H2O2 formed in the culture medium was a likely facilitator of these effects. Necrosis and autophagy were recorded in primary cells, whereas cell lines exhibited apoptosis and necrosis.Conclusions:This study demonstrates that LTP treatment causes cytotoxic insult in primary prostate cells, leading to rapid necrotic cell death. It also highlights the need to study primary cultures in order to gain more realistic insight into patient response.

Fibroblast Cell Morphology Altered by Low-Temperature Atmospheric Pressure Plasma

Low-temperature atmospheric pressure plasmas (LTAPPs) have garnered great scientific interest in recent years because of their chemically reactive properties. The LTAPP is currently being studied for potential applications in the field of plasma medicine including, but not limited to, wound healing and cancer therapy. In this paper, images of fibroblast cells exposed to different treatment times of LTAPP are presented. The results reveal the morphological cell changes associated with LTAPP treatment and indicate the potential use of LTAPP to alter physical attributes of mammalian cells.

Special Issue on Nonthermal Medical/Biological Applications Using Ionized Gases and Electromagnetic Fields

This is the seventh Special Issue of IEEE Transactions on Plasma Science on the biomedical applications of ionized gases and electromagnetic fields. A total of seven excellent and exciting papers covers the intersection between biomedicine and plasmas/electromagnetic fields. The special issue papers encompass a wide range of research that include work on the decontamination of human extremities, inactivation of different microbial organisms, and the interaction of cells to plasma-modified surfaces. Furthermore, the manuscripts include work on the plasma-generated active chemical species and their effects on mammalian cells, and a study on the effect of atmospheric-pressure plasma on the structure and the function of a digestive enzyme, i.e., pepsin. It is hoped that the state-of-the-art studies in this Special Issue further advance the technology and attract more and more researchers outside our traditional plasma science community. The first Special Issue on Nonthermal Medical/Biological Applications Using Ionized Gases and Electromagnetic Fields was published 12 years ago, following ElectroMed99, one of the first international symposiums on the research field. Since then, the special issues have attracted an enormous number of readers in a variety of fields every two years. In the early 2000s, most of the papers published in the special issues had been written primarily by plasma scientists. Over the past decade, we have observed a dramatic increase in the number of collaborative papers written in conjunction with biologists, biochemists, and medical/dental doctors. The multidisciplinary teams are particularly important and essential to understanding of the fundamental mechanisms and realizing the practical applications of low-temperature atmospheric-pressure plasmas and high-power ultrashort electrical pulses in biology and medicine.

Atomic-scale simulations of reactive oxygen plasma species interacting with bacterial cell walls

In recent years there has been growing interest in the use of low-temperature atmospheric pressure plasmas for biomedical applications. Currently, however, there is very little fundamental knowledge regarding the relevant interaction mechanisms of plasma species with living cells. In this paper, we investigate the interaction of important plasma species, such as O3, O2 and O atoms, with bacterial peptidoglycan (or murein) by means of reactive molecular dynamics simulations. Specifically, we use the peptidoglycan structure to model the gram-positive bacterium Staphylococcus aureus murein. Peptidoglycan is the outer protective barrier in bacteria and can therefore interact directly with plasma species. Our results demonstrate that among the species mentioned above, O3 molecules and especially O atoms can break important bonds of the peptidoglycan structure (i.e. C–O, C–N and C–C bonds), which subsequently leads to the destruction of the bacterial cell wall. This study is important for gaining a fundamental insight into the chemical damaging mechanisms of the bacterial peptidoglycan structure on the atomic scale.

Modeling the chemical kinetics of atmospheric plasma for cell treatment in a liquid solution

Low temperature atmospheric pressure plasmas have been known to be effective for living cell inactivation in a liquid solution but it is not clear yet which species are key factors for the cell treatment. Using a global model, we elucidate the processes through which pH level in the solution is changed from neutral to acidic after plasma exposure and key components with pH and air variation. First, pH level in a liquid solution is changed by He+ and He(21S) radicals. Second, O3 density decreases as pH level in the solution decreases and air concentration decreases. It can be a method of removing O3 that causes chest pain and damages lung tissue when the density is very high. H2O2, HO2, and NO radicals are found to be key factors for cell inactivation in the solution with pH and air variation.

Portable nanosecond pulsed air plasma jet

Low-temperature atmospheric pressure plasmas are of great importance in many emerging biomedical and materials processing applications. The redundancy of a vacuum system opens the gateway for highly portable plasma systems, for which air ideally becomes the plasma-forming gas and remote plasma processing is preferred to ensure electrical safety. Typically, the gas temperature observed in air plasma greatly exceeds that suitable for the processing of thermally liable materials; a large plasma-sample distance offers a potential solution but suffers from a diluted downstream plasma chemistry. This Letter reports a highly portable air plasma jet system which delivers enhanced downstream chemistry without compromising the low temperature nature of the discharge, thus forming the basis of a powerful tool for emerging mobile plasma applications.

Biomedical Applications of Low Temperature Atmospheric Pressure Plasmas to Cancerous Cell Treatment and Tooth Bleaching

Low temperature atmospheric pressure plasmas have attracted great interests and they have been widely applied to biomedical applications to interact with living tissues, cells, and bacteria due to their non-thermal property. This paper reviews the biomedical applications of low temperature atmospheric pressure plasmas to cancerous cell treatment and tooth bleaching. Gold nanoparticles conjugated with cancer-specific antibodies have been introduced to cancerous cells to enhance selective killing of cells, and the mechanism of cell apoptosis induced by plasma has been investigated. Tooth exposed to helium plasma jet with hydrogen peroxide has become brighter and the productions of hydroxyl radicals from hydrogen peroxide have been enhanced by plasma exposure.

Biomedical Applications of Low Temperature Atmospheric Pressure Plasmas to Cancerous Cell Treatment and Tooth Bleaching

Biomedical Applications of Low Temperature Atmospheric Pressure Plasmas to Cancerous Cell Treatment and Tooth Bleaching

A plasma needle for generating homogeneous discharge in atmospheric pressure air

Homogeneous discharge in air is often considered to be the ultimate low-temperature atmospheric pressure plasmas for industrial applications. In this paper, we present a method whereby stable homogeneous discharge in open air can be generated by a simple plasma needle. The discharge mechanism is discussed based on the spatially resolved light emission waveforms from the plasma. Optical emission spectroscopy is used to determine electron energy and rotational temperature, and results indicate that both electron energy and rotational temperature increase with increasing the applied voltage. The results are analyzed qualitatively based on the discharge mechanism.

Sterilization Techniques for Soil Remediation and Agriculture Based on Ozone and AOP

AbstractThe sterilizing and remediation effects of the non-equilibrium atmospheric pressure plasmas are known for decades. Low temperature atmospheric pressure plasmas are considered as a promising alternative to conventional sterilizing methods, which have numerous drawbacks. Influence of various parameters such as discharge regimes, reactor geometries, gases, etc., on formation and effectiveness of plasma were investigated by many research groups. This paper presents the review of recently developed, environmentally safe technologies applied for the agriculture and soil remediation. The results of ozone soil sterilization and ozone influence on the DNA structure of Escherichia coli are described. The results of oxidants’ influence on humic acid are presented.