Dielectric Barrier Discharge Plasma Jet Research Articles

Dielectric barrier discharge and jet type plasma surface modifications of hybrid polymeric poly (ε-caprolactone)/chitosan scaffolds.

In this study, dry air plasma jet and dielectric barrier discharge Ar + O2 or Ar + N2 plasma modifications and their effects on wettability, topography, functionality and biological efficiency of the hybrid polymeric poly (ε-caprolactone)/chitosan scaffolds were reported. The samples treated with Ar + O2 dielectric barrier discharge plasma (80 sccm O2 flow rate, 3-min treatment) or with dry air plasma jet (15-cm nozzle-sample distance, 13-min treatment) had the closest wettability (49.11 ± 1.83 and 53.60 ± 0.95, respectively) to the commercial tissue culture polystyrene used for cell cultivation. Scanning electron microscopy images and X-ray photoelectron spectrometry analysis showed increase in topographical roughness and OH/NH2 functionality, respectively. Increased fluid uptake capacity for the scaffolds treated with Ar + O2 dielectric barrier discharge plasma (73.60% ± 1.78) and dry air plasma jet (72.48% ± 0.75) were also noted. Finally, initial cell attachment as well as seven-day cell viability, growth and proliferation performances were found to be significantly better for both plasma treated scaffolds than for untreated scaffolds.

Research progress of metal catalysts enhanced synthesized by cold plasma

Cold plasma is a kind of non-thermal plasma, and characterized by high electron temperature (1-10 eV) and low gas temperature, which can be close to room temperature. It has been proved to be a fast, facile and environmentally friendly new method for synthesizing supported metal catalysts. Enhanced synthesis of metal catalysts by cold plasma consists of complex physical and chemical reactions. On the one hand, the active environment provided by cold plasma, can not only speed up the chemical reactions, shorten the reaction time from a few hours to several minutes, but also realize the kinetically or thermodynamically infeasible chemical reactions to achieve unconventional preparation. On the other hand, the phase contact behavior on a mesoscopic scale is influenced during cold plasma enhanced preparation, thereby the metal catalysts with structure different from that synthesized by traditional method. This review summarizes the reactor structure, physical and chemical mechanism for synthesizing metal catalysts by cold plasma, as well as the structure characteristics of the obtained metal catalysts. According to the working pressure, cold plasma can be categorized into low-pressure (LP) cold plasma and atmospheric-pressure (AP) cold plasma. The LP cold plasma is often generated by radio frequency glow discharge or direct current glow discharge, while the AP cold plasma is generally generated by dielectric barrier discharge and AP cold plasma jet. Energetic electrons are deemed to be the reducing agents for LP cold plasma. However, due to the frequent collisions among the electrons and gas molecules at atmospheric pressure, the electron energy in AP cold plasma is not high enough to reduce the metal ions directly. Therefore, hydrogen-containing gases are often adopted to generate active hydrogen species to reduce the metal ions. The process of synthesizing the metal catalysts by using the cold plasma is a fast, low-temperature process, and in the preparation process there exists a strong Coulomb repulsion. Therefore, metal catalysts with small size and high dispersion of metal nanoparticles, strong metal-support interaction, as well as specific metal structures (alloying degree and crystallinity) and modified supports can be obtained. Correspondingly, metal catalysts with high catalytic activity and stability can be synthesized. In addition, the challenges of preparing the cold plasma are discussed, and the future development is also prospected.

Long‐lasting oil wettability patterns fabrication on superoleophobic surfaces by atmospheric pressure DBD plasma jet

Water wettability patterns on superhydrophobic surfaces have been widely designed to meet requirements of many fields, such as lab-on-a-chip devices and bioengineering. However, these systems are easily invalidated by oily liquids. Therefore, oil wettability patterns, which have rarely been focused on, are urgently needed. In this work, the authors successfully control oil wettability of superoleophobic surface by an atmospheric pressure dielectric barrier discharge (DBD) plasma jet. The results indicate that oil wettability is strongly influenced by treatment time, applied voltage and distance between plasma jet outlet and samples. They find that superoleophobic surfaces can be modified to be superoleophilic within 15 s, and that small holes can be etched on the surfaces under high applied voltages. Then, superoleophobic-superoleophilic patterns are prepared via selective plasma jet irradiation on superoleophobic surfaces, and both directional and antigravity transport of water and oily liquids are thus realised without external electrical or magnetic field. Additionally, ageing experiments show that the plasma-treated areas can maintain the induced wettability for >30 days storing under normal ambients, demonstrating superior time stability. The results presented here show the potential of atmospheric pressure DBD plasma jet for rapid oil wettability control and fabrication of long-time-effective oil wettability patterns.

Enhanced energy transfer efficiency in a four-electrodes configuration DBD plasma jet

In this work a dielectric barrier discharge (DBD) plasma jet that uses a multiple electrodes configuration is investigated. The results show that both plasma power and its rotational and vibrational temperatures tend to increase with the number of powered electrodes in the DBD device. The emission intensities of the excited species in the plasma, and consequently their number density, also grow as a function of the number of powered electrodes. Based on these facts and since the electric power provided by the power supply was kept constant, there is an indication that the use of multiple electrodes improves the energy efficiency of the device.

Nontarget Biomolecules Alter Macromolecular Changes Induced by Bactericidal Low-Temperature Plasma.

Low-temperature plasmas (LTPs) have a proven bactericidal activity governed by the generated reactive oxygen and nitrogen species (RONS) that target microbial cell components. However, RONS also interact with biomolecules in the environment. Here we assess the impact of these interactions upon exposure of liquid suspensions with variable organic content to an atmospheric-pressure dielectric barrier discharge plasma jet. Salmonella enterica serovar Typhimurium viability in the suspension was reduced in the absence [e.g., phosphate buffered saline (PBS)], but not in the presence of (high) organic content [Dulbecco's Modified Eagle's Medium (DMEM), DMEM supplemented with foetal calf serum, and Lysogeny Broth]. The reduced viability of LTP-treated bacteria in PBS correlated to a loss of membrane integrity, whereas double-strand DNA breaks could not be detected in treated single cells. The lack of bactericidal activity in solutions with high organic content correlated with a relative decrease of •OH and O3/O2(a1n}{}{Delta }text{g}n)/O, and an increase of H2O2 and n}{}mathrm{NO}_{2}^{-}n in the plasma-treated solutions. These results indicate that the redox reactions of LTP-generated RONS with nontarget biomolecules resulted in a RONS composition with reduced bactericidal activity. Therefore, the chemical composition of the bacterial environment should be considered in the development of LTP for antimicrobial treatment, and may affect other biomedical applications as well.

Structural and functional analysis of lysozyme after treatment with dielectric barrier discharge plasma and atmospheric pressure plasma jet

The variation in the biological function of proteins plays an important role in plasma medicine and sterilization. Several non-thermal plasma sources with different feeding gases are used worldwide for plasma treatment, including dielectric barrier discharge (DBD) and atmospheric-pressure plasma jet (APPJ) as the most commonly used sources. Therefore, in the present work, we used both DBD and APPJ plasma sources with N2 and air as feeding gases to evaluate the effects on the structural, thermodynamic, and activity changes of enzymes. In the current work, we used lysozyme as a model enzyme and verified the structural changes using circular dichroism (CD), fluorescence, and X-ray crystallography. In addition, we investigated the lysozyme thermodynamics using CD thermal analysis and changes in the B-factor from X-ray crystallography. The results showed that lysozyme activity decreased after the plasma treatment. From these analyses, we concluded that N2-feeding gas plasma disturbs the structure and activity of lysozyme more than Air feeding gas plasma in our experimental studies. This study provides novel fundamental information on the changes to enzymes upon plasma treatment, which has been absent from the literature until now.

Changes in Properties of Dielectric Barrier Discharge Plasma Jets for Different Gases and for Insulating and Conducting Transfer Plates

Dielectric Barrier Discharge (DBD) plasma jets has been studied extensively in recent years because of its wide range of applications. DBD plasmas can be produced using many different gases and can be applied to a broad variety of surfaces and substrates. In this work, we provide a comparison of DBD plasmas generated using argon (Ar), helium (He) and nitrogen (N2), as well as their mixtures with water vapor in order to know how some plasma properties are affected by the use of different gases. All plasmas were studied in two different conditions, using a transfer plate made of a conductive material and using a transfer plate made of an insulating one. We observed that the processes of excitation and ionization of nitrogen molecules by direct collisions with Ar or He are more evident and significant in He plasmas, which means that He atoms in metastable states have greater ability to transfer energy to molecules of nitrogen in the plasma. The collisions of He atoms in metastable states with N2 molecules determine the vibrational temperature (Tvib) values in He plasmas, while in Ar and N2 plasmas the Tvib values are determined mainly by collisions of electrons with N2 molecules.

Comparison Between Conventional and Transferred DBD Plasma Jets for Processing of PDMS Surfaces

In this work we studied processing of poly(dimethylsiloxane) (PDMS) surfaces using dielectric barrier discharge (DBD) plasma in two different assemblies, one using the primary plasma jet obtained from a conventional DBD and the other using a DBD plasma jet transfer. The evolution of water contact angle (WCA) in function of plasma processing time and in function of aging time as well as the changes in the surface roughness of PDMS samples for both plasma treatments have been studied. We also compared vibrational and rotational temperatures for both plasmas and for the first time the vibrational temperature (T_vib) for the transferred plasma jet has been shown to be higher as compared with the primary jet. The increment in the T_vib value seems to be the main reason for the improvements in adhesion properties and surface wettability for the transferred plasma jet. Possible explanations for the increase in the vibrational temperature are presented.

Spatial Dependence of DNA Damage in Bacteria due to Low-Temperature Plasma Application as Assessed at the Single Cell Level

Low temperature plasmas (LTPs) generate a cocktail of reactive nitrogen and oxygen species (RNOS) with bactericidal activity. The RNOS however are spatially unevenly distributed in the plasma. Here we test the hypothesis that this distribution will affect the mechanisms underpinning plasma bactericidal activity focussing on the level of DNA damage in situ. For the first time, a quantitative, single cell approach was applied to assess the level of DNA damage in bacteria as a function of the radial distance from the centre of the plasma jet. Salmonella enterica on a solid, dry surface was treated with two types of LTP: an atmospheric-pressure dielectric barrier discharge plasma jet (charged and neutral species) and a radio-frequency atmospheric-pressure plasma jet (neutral species). In both cases, there was an inverse correlation between the degree of DNA damage and the radial distance from the centre of the plasma, with the highest DNA damage occurring directly under the plasma. This trend was also observed with Staphylococcus aureus. LTP-generated UV radiation was eliminated as a contributing factor. Thus valuable mechanistic information can be obtained from assays on biological material, which can inform the development of LTP as a complementary or alternative therapy for (topical) bacterial infections.

Analysis of Ar plasma jets induced by single and double dielectric barrier discharges at atmospheric pressure

The aim is the comparison of different plasma parameters of single and double dielectric barrier discharge plasma jet configurations (S-DBD and D-DBD) which are potentially usable in biomedical applications. Both configurations are studied in terms of electric field distribution, electrical discharge characteristics, plasma parameters (estimated by optical emission spectroscopy analysis), and hydrodynamics of the plasma jet for electrical parameters of power supplies corresponding to an applied voltage of 10 kV, pulse duration of 1 μs, frequency of 9.69 kHz, and Ar flow of 2 l/min. We observed that the D-DBD configuration requires half the electrical power one needs to provide in the S-DBD case to generate a plasma jet with similar characteristics: excitation temperature around 4700 K, electron density around 2.5 × 1014 cm−3, gas temperature of about 320 K, a relatively high atomic oxygen concentration reaching up to 1000 ppm, the presence of reactive oxygen and nitrogen species (nitric oxide, hydroxyl radical, and atomic oxygen), and an irradiance in the UV-C range of about 20 μW cm−2. Moreover, it has been observed that D-DBD plasma jet is more sensitive to short pulse durations, probably due to the charge accumulation over the dielectric barrier around the internal electrode. This results in a significantly longer plasma length in the D-DBD configuration than in the S-DBD one up to a critical flow rate (2.25 l/min) before the occurrence of turbulence in the D-DBD case. Conversely, ionization wave velocities are significantly higher in the S-DBD setup (3.35 × 105 m/s against 1.02 × 105 m/s for D-DBD), probably due to the higher electrostatic field close to the high voltage electrode in the S-DBD plasma jet.

Surface modification of aluminium alloys by atmospheric pressure plasma treatments for enhancement of their adhesion properties

This work deals with surface modification of aluminium alloy AA7075 by two types of atmospheric pressure plasma: dielectric barrier discharge (DBD) and atmospheric pressure plasma jet (APPJ) with the purpose to enhance the adhesion of polyurethane coating on the alloy. The surface characterization was performed by using water contact angle, roughness and surface free energy measurements. Quality of the coating was tested according to the adhesion tape test (ASTM D3359) and evaluated by electrochemical techniques. The aluminium alloy showed great improvement of the surface wettability after plasma treatments. While, the adhesion tape test presented excellent results with perfect adhesion, meaning that both plasma treatments were efficient in improving the adhesion of the polyurethane coating to the AA7075. The Fourier Transform Infrared Spectroscopy (FTIR) results demonstrated that the plasma treatment cleaned the Al alloy surface by removing hydrocarbon contaminations. Both polarization curves and Electrochemical Impedance Spectroscopy (EIS) results showed better characteristics of corrosion resistance for polyurethane-coated AA7075 than untreated coated samples.

An in situ and downstream study of non-thermal plasma chemistry in an air fed dielectric barrier discharge (DBD)

This paper reports a spectroscopic study of non-thermal plasma chemistry in an air-fed dielectric barrier discharge (DBD) plasma jet. In situ analysis (i.e. the analysis of the plasma glow) and downstream analysis were carried out to identify and monitor species produced in the plasma as they propagate from the plasma glow to downstream regions. The analyses were carried out using Fourier Transform InfraRed (FTIR) and UV–Vis spectroscopies. The species: O3, N2O5, N2O, HNO3, CO2, CO and, for the first time, a vibrationally excited form of CO2 (i.e. (v)) were identified in the plasma glow, while O3, N2O5, HNO3 and N2O were detected in the downstream exhaust. The behaviour of these species was monitored as a function of a range of experimental conditions including: input power, gas flow rate, relative humidity, gas temperature and feed gas composition. In addition, the uncertainty associated with UV–vis detection of ozone in the presence of N2O5 and/or HNO3 as interfering species was determined.

Comparative Studies of Double Dielectric Barrier Discharge and Microwave Argon Plasma Jets at Atmospheric Pressure for Biomedical Applications

Two low-temperature plasma jets using argon carrier gas at atmospheric pressure have been experimentally characterized using optical emission diagnostics. The first one is a double dielectric barrier discharge (DBD) plasma jet generated by a pulsed power supply (9 kV, 9.69 kHz, duty cycle: 1%) and the second one is a microwave (MW) induced plasma jet (2.45 GHz, 40 W ). The argon gas (4.5 purity) flowing through the quartz tube used to launch the plasma in open air is kept at 1 L/min for both plasma devices. Some thermodynamic parameters such as rotation ( $T_{\rm rot}$ ) and excitation ( $T_{\rm exc}$ ) temperatures have been determined as well as some plasma active species such as electron density, ultraviolet C (UVC) irradiance, and atomic oxygen concentrations. Most of these plasma parameters are spatially resolved along the plasma jet axis using the spectra of atomic lines (Ar and O) in the visible range and molecular bands (N2 and OH) in the UV range. At the tube outlet, the electron density and atomic oxygen concentration are one decade higher in the case of the dielectric barrier discharges (DBDs) plasma jet while $T_{\rm rot}$ is higher in the case of the MW plasma jet. These differences are mainly due to the way of plasma generation. Indeed, the guided-ionization waves generated by the DBD setup cause higher nonequilibrium phenomena since the difference between $T_{\rm rot}$ and $T_{\rm exc}$ is shown to be much larger in the DBD case. Furthermore, at the tube outlet, it is shown that UVC irradiance produced by the MW plasma jet is about twice as large as that of the DBD plasma jet. However, at 1.7 cm away from the tube outlet, the differences between the two plasma setups on temperatures and active species production become less significant. For instance, the plasma gas temperature measured with a thermocouple becomes the same (320 K) showing the ability of both plasma setups to be used in biomedical applications without inducing a significant thermal effect.

Effects of air transient spark discharge and helium plasma jet on water, bacteria, cells, and biomolecules.

Atmospheric pressure DC-driven self-pulsing transient spark (TS) discharge operated in air and pulse-driven dielectric barrier discharge plasma jet (PJ) operated in helium in contact with water solutions were used for inducing chemical effects in water solutions, and the treatment of bacteria (Escherichia coli), mammalian cells (Vero line normal cells, HeLa line cancerous cells), deoxyribonucleic acid (dsDNA), and protein (bovine serum albumin). Two different methods of water solution supply were used in the TS: water electrode system and water spray system. The effects of both TS systems and the PJ were compared, as well as a direct exposure of the solution to the discharge with an indirect exposure to the discharge activated gas flow. The chemical analysis of water solutions was performed by using colorimetric methods of UV-VIS absorption spectrophotometry. The bactericidal effects of the discharges on bacteria were evaluated by standard microbiological plate count method. Viability, apoptosis and cell cycle were assessed in normal and cancerous cells. Viability of cells was evaluated by trypan blue exclusion test, apoptosis by Annexin V-FITC/propidium iodide assay, and cell cycle progression by propidium iodide/RNase test. The effect of the discharges on deoxyribonucleic acid and protein were evaluated by fluorescence and UV absorption spectroscopy. The results of bacterial and mammalian cell viability, apoptosis, and cell cycle clearly show that cold plasma can inactivate bacteria and selectively target cancerous cells, which is very important for possible future development of new plasma therapeutic strategies in biomedicine. The authors found that all investigated bio-effects were stronger with the air TS discharge than with the He PJ, even in indirect exposure.

Low and atmospheric plasma polymerisation of nanocoatings for bio-applications

There exists an abundant literature on polymers used for biomedical applications. However, the research described in this article deals with the plasma (co)polymerisation of different organic precursors for surface modifications of a variety of substrates in order to tailor the physico-chemical properties of the substrates for tuneable biomolecule–surface interactions. The major part of the work presented focuses on the low-pressure inductively excited plasma-enhanced chemical vapour deposition of organic precursors for the functionalisations of material. In the second part of the article, an open-air custom-made atmospheric-pressure dielectric barrier discharge (DBD) plasma jet is discussed for the anti-fouling applications. This special focus aims to elaborate the state of the art of different low and atmospheric pressure plasma-deposited polymers for anti-fouling applications, cell–surface interactions and tissue engineering applications.

Hydrophobic–Hydrophilic Character of Hexamethyldisiloxane Films Polymerized by Atmospheric Pressure Plasma Jet

This paper reports on polymerization of hexamethyldisiloxane (HMDSO) using an atmospheric pressure dielectric barrier discharge plasma jet. The aim of the study is to contribute to the knowledge of thin film deposition using a low cost technique of atmospheric pressure plasma. The monomer HMDSO was used as a precursor for polymerization. The discharge was powered using a laboratory made resonant power supply working with sinusoidal voltage signal at a frequency of 8 kHz. The coatings were characterized using Fourier transform infrared spectroscopy, atomic force microscopy, growth rates and surface free energy measurements. The hydrophobic nature of the films was found to be decreased with increasing the plasma power. Fourier transform infrared spectroscopy gave an indication of the dominated inorganic content of the surface at higher discharge. An average growth rate of 220 nm min−1 was achieved at a monomer flow rate of 5 sccm and discharge power of 12.5 W. The films obtained using plasma jet were found to be stable in aqueous media and well adhered with substrate.

Influence of He Gas Flow Rate on Optical Emission Characteristics in Atmospheric Dielectric-Barrier-Discharge Plasma Jet

We present here the analysis of the characteristics of a dielectric-barrier-discharge (DBD) plasma jet in open air using the optical emission spectroscopy (OES). The OES on oxygen emission is useful to estimate the presence of reactive excited O atoms. The O emission intensity is much higher near the quartz-tube outlet and abruptly decreases with distance from the quartz tube. Our experiments also show that the DBD plasma jet is quite sensitive to He gas flow rate (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">He-gas flow</sub> ): increasing R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">He-gas flow</sub> induces weak pulse discharge, resulting in decreasing O emission intensity.

Characterization of an asymmetric DBD plasma jet source at atmospheric pressure

Non-thermal atmospheric pressure plasma jets or plasma plumes have recently been largely investigated in applications like materials processing, biomedical treatment and analytical chemistry. In this paper He-discharges in an asymmetrical Dielectric Barrier Discharge (DBD) have been experimentally studied with an Intensified Charge Coupled Device (ICCD) camera, Optical Emission Spectroscopy (OES) and Time-Of-Flight Mass Spectrometry (TOF-MS) measurements. The development of the plasma plume, its apparent length and the spatial distribution of the excited and ionized species along the plasma plume have been characterized as a function of the applied voltage and the gas flow rate. A TOF-MS spectrometer has been used to characterize ionized species (positive and negative ions) produced by the plasma alone and the plasma with addition of ethanol, both as a function of the distance between the plasma plume and the vacuum interface of the spectrometer.

An Atmospheric Cold Plasma Jet With a Good Uniformity, Robust Stability, and High Intensity Over a Large Area

To gain a cold atmospheric pressure helium plasma jet with good uniformity, robust stability, and high intensity over a larger area, a novel dielectric barrier discharge plasma jet generator with a honeycomb-like powered electrode and a gas shielding is proposed in this paper. The innovative design has been demonstrated to facilitate more homogeneous treatment and a higher degree of insusceptibility in plasma stability to variations of samples in their material properties, physical dimensions, and structures.

Atmospheric pressure plasma jet with high-voltage power supply based on piezoelectric transformer.

The dielectric barrier discharge plasma jet, an example of the nonthermal atmospheric pressure plasma jet (APPJ), generates low-temperature plasmas that are suitable for the atomization of volatile species and can also be served as an ionization source for ambient mass and ion mobility spectrometry. A new design of APPJ for mass spectrometry has been built in our group. In these plasma sources magnetic transformers (MTs) and inductors are typically used in power supplies but they present several drawbacks that are even more evident when dealing with high-voltage normally used in APPJs. To overcome these disadvantages, high frequency generators with the absence of MT are proposed in the literature. However, in the case of miniaturized APPJs these conventional power converters, built of ferromagnetic cores and inductors or by means of LC resonant tank circuits, are not so useful as piezoelectric transformer (PT) based power converters due to bulky components and small efficiency. We made and examined a novel atmospheric pressure plasma jet with PT supplier served as ionization source for ambient mass spectrometry, and especially mobile spectrometry where miniaturization, integration of components, and clean plasma are required. The objective of this paper is to describe the concept, design, and implementation of this miniaturized piezoelectric transformer-based atmospheric pressure plasma jet.