Low-temperature Atmospheric Plasma Research Articles

In-situ monitoring of etching of bovine serum albumin using low-temperature atmospheric plasma jet

Bio-decontamination of surfaces by means of atmospheric pressure plasma is nowadays extensively studied as it represents promising alternative to commonly used sterilization/decontamination techniques. The non-equilibrium atmospheric pressure plasmas were already reported to be highly effective in removal of a wide range of biological residual from surfaces. Nevertheless the kinetics of removal of biological contamination from surfaces is still not well understood as the majority of performed studies were based on ex-situ evaluation of etching rates, which did not allow investigating details of plasma action on biomolecules. This study therefore presents a real-time, in-situ ellipsometric characterization of removal of bovine serum albumin (BSA) from surfaces by low-temperature atmospheric plasma jet operated in argon. Non-linear and at shorter distances between treated samples and nozzle of the plasma jet also non-monotonic dependence of the removal rate on the treatment duration was observed. According to additional measurements focused on the determination of chemical changes of treated BSA as well as temperature measurements, the observed behavior is most likely connected with two opposing effects: the formation of a thin layer on the top of BSA deposit enriched in inorganic compounds, whose presence causes a gradual decrease of removal efficiency, and slight heating of BSA that facilitates its degradation and volatilization induced by chemically active radicals produced by the plasma.

Physicochemical properties of bactericidal plasma-treated water

Plasma-treated water (PTW), i.e. distilled water (DW) exposed to low-temperature atmospheric pressure helium plasma, exhibited strong bactericidal activity against Escherichia coli in suspension even within a few minutes of preparation. This effect was enhanced under acidic conditions. The bactericidal activity of PTW was attenuated according to first-order kinetics and the half-life was highly temperature dependent. The electron spin resonance (ESR) signal of an adduct of the superoxide anion radical () was detected in an aqueous solution using a spin-trapping reagent mixed with PTW, and adding superoxide dismutase to the PTW resulted in a loss of the bactericidal activity and weakening of the ESR adduct signal of in the spin-trapping. These results suggest that plays an important role in imparting bactericidal activity to PTW. Moreover, molecular nitrogen was required both in the ambient gas and in the DW used to prepare the PTW. We, therefore, suggest that the reactive molecule in PTW with bactericidal effects is not a free reactive oxygen species but nitrogen atom(s)-containing molecules that release , such as peroxynitrous acid (ONOOH) or peroxynitric acid (O2NOOH). Considering the activation energy for degradation of these species, we conclude that peroxynitric acid stored in PTW induces the bactericidal effect.

Influence of low-temperature plasma and γ radiation on the surface properties of PET track membranes

Physical and chemical properties of the surfaces of polyethylene-terephthalate (PET) track membranes (TMs) exposed to low-temperature atmospheric plasma and to γ radiation produced by 60Co isotopes are studied. It is established that the exposure to plasma leads to changes in the chemical composition of the surface and increases the number of polar (carbonyl and carboxyl) functional groups in a thin near-surface layer of a TM. The surface energy is also shown to grow owing to its polar component and surface reconstruction. The reconstruction consists in the growth of surface roughness owing to oxidation-reduction reactions, followed by the appearance of destructive areas. These changes promote a lyophilic behavior of the track-membrane surface. Subsequent γ irradiation of the surface is shown to reduce the plasma-modified TM undulation, while decreasing the number of destructive areas and bringing the material into a more equilibrium state.

Antimicrobial Effect of Low Temperature Atmospheric Plasma against Oral Pathogens

Antimicrobial Effect of Low Temperature Atmospheric Plasma against Oral Pathogens

Preface to Special Topic: Plasmas for Medical Applications

Intense research effort over last few decades in low-temperature (or cold) atmospheric plasma application in bioengineering led to the foundation of a new scientific field, plasma medicine. Cold atmospheric plasmas (CAP) produce various chemically reactive species including reactive oxygen species (ROS) and reactive nitrogen species (RNS). It has been found that these reactive species play an important role in the interaction of CAP with prokaryotic and eukaryotic cells triggering various signaling pathways in cells.

A handheld low temperature atmospheric pressure air plasma gun for nanomaterial synthesis in liquid phase

A handheld low temperature atmospheric pressure air plasma gun based on a dielectric barrier structure with hollow electrodes was proposed. The portable plasma gun with an embedded mini air pump was driven by a 12 V direct voltage battery. The air plasma jet generated from the gun could be touched without a common shock hazard. Besides working in air, the plasma gun can also work in water. The diagnostic result of optical emission spectroscopy showed the difference in reactive species of air plasma jet between in air and in water. The plasma gun was excited in 20 ml chloroauric acid aqueous solution with a concentration of 1.214 mM. A significant amount of gold nanoparticles were synthesized after 2 min continuous discharge. The plasma gun with these unique features is applicable in plasma medicine, etching, and s-nthesis of nanomaterials.

Characteristics in the jet region of helium radio-frequency atmospheric-pressure glow discharge with array generators

The two-dimensional spatially extended atmospheric plasma arrays by many parallel radio-frequency glow discharge plasma jets packed densely, represent a feature option of large-scale low-temperature atmospheric plasma technologies with distinct capability of directed delivery of reactive species and good insusceptibility to sample variations. However, it is still a challenge to form plasma jet with large area of uniform active species on a downstream substrate due to the complex interactions between individual jets. This paper proposes to numerically study the strategy and mechanism of control/modulation for the array discharge to produce two-dimensional plasma uniformity in the downstream working area. In this work, a two dimensional fluid model is employed to investigate the characteristics in the jet region of helium radio-frequency atmospheric-pressure glow discharge (RF APGD) with array generators. The influences of upstream discharge characteristics, gas flow and their cooperative effects on the distribution of species densities, gas temperatures and the uniformity of active species in the material treating area is studied, and the essential strategy for the modulation method is acquired. The results will be significant for deep understanding of coupling behaviors of multiple plasma plumes in the RF APGD array and applications of the technology.

Dielectric barrier structure with hollow electrodes and its recoil effect

A dielectric barrier structure with hollow electrodes (HEDBS), in which gas flow oriented parallel to the electric field, was proposed. Results showed that with this structure, air can be effectively ignited, forming atmospheric low temperature plasma, and the proposed HEDBS could achieve much higher electron density (5 × 1015/cm3). It was also found that the flow condition, including outlet diameter and flow rate, played a key role in the evolution of electron density. Optical emission spectroscopy diagnostic results showed that the concentration of reactive species had the same variation trend as the electron density. The simulated distribution of discharge gas flow indicated that the HEDBS had a strong recoil effect on discharge gas, and could efficiently promote generating electron density as well as reactive species.

Acoustic Measurements in a Hexamethyldisiloxane-Loaded Low-Temperature Direct Barrier Discharge (DBD) Plasma Effluent: Nozzle Cleaning

Acoustic emission (AE) measurements as well as laser light scattering experiments were performed during SiO2 layer deposition. SiO2 was generated in low-temperature atmospheric plasma torches (≤500 W), which were seeded with hexamethyldisiloxane. These AE measurements can be used to detect the necessity for nozzle cleaning online. The plasma torches were used to obtain high-quality SiO2 coatings. For electrical power of less than 350 W, we observed parasitic SiO2 deposition in the burner nozzle, which decreases the nozzle aperture within several hours of operation time. No parasitic SiO2 deposition inside the burner nozzle was observed when the plasma source was operated at more than 350 W. The reduced nozzle aperture causes increased plasma velocities and acoustic noise. Especially burst-like increases of this acoustic emission were assumed to be correlated to the ejection of particles. This hypothesis could be confirmed by measurements of scattered light from a sheet of laser light at 248 nm. The obtained correlations suggest using a microphone as a low-cost monitor for the degree of parasitic deposition inside the plasma burner nozzle. The threshold for acoustic noise detection has to be chosen low enough to avoid burst-like emission of particles.

Non-thermal plasma mills bacteria: Scanning electron microscopy observations

Non-thermal plasmas hold great promise for a variety of biomedical applications. To ensure safe clinical application of plasma, a rigorous analysis of plasma-induced effects on cell functions is required. Yet mechanisms of bacteria deactivation by non-thermal plasma remain largely unknown. We therefore analyzed the influence of low-temperature atmospheric plasma on Gram-positive and Gram-negative bacteria. Using scanning electron microscopy, we demonstrate that both Gram-positive and Gram-negative bacteria strains in a minute were completely destroyed by helium plasma. In contrast, mesenchymal stem cells (MSCs) were not affected by the same treatment. Furthermore, histopathological analysis of hematoxylin and eosin–stained rat skin sections from plasma–treated animals did not reveal any abnormalities in comparison to control ones. We discuss possible physical mechanisms leading to the shred of bacteria under non-thermal plasma irradiation. Our findings disclose how helium plasma destroys bacteria and demonstrates the safe use of plasma treatment for MSCs and skin cells, highlighting the favorability of plasma applications for chronic wound therapy.

Inactivation of Biofilms Using a Low Power Atmospheric Pressure Argon Plasma Jet; the Role of Entrained Nitrogen

The inactivation of microbial biofilms using a low temperature atmospheric pressure argon plasma jet is investigated. The treatment of Staphylococcus aureus biofilms was the most effective; 78% population reduction was reached within 3 min. Higher reduction rates were found for smaller plasma‐sample distances and for longer exposure time. Employing a pretreatment of the samples with ascorbic acid suggests that oxygen radicals might play a role in the inactivation process. A novel method for the quantitative analysis of spectra is introduced. It points towards an important role of entrained nitrogen and shows that excited nitrogen species are created in large abundances. These species can be important carriers of excitation energy to the biofilms or may function as important intermediate reactive species.

Retardation of C2C12 myoblast cell proliferation by exposure to low-temperature atmospheric plasma.

As the first step in evaluating the possibility of low-temperature atmospheric plasma for clinical applications in the treatment of rhabdomyosarcoma (RMS), we determined the effects of plasma exposure on C2C12 myoblasts. The low-temperature atmospheric plasma was generated through an electrical discharge in argon gas. One minute of plasma exposure every 24h inhibited the cell proliferation, whereas myoblast differentiation was not affected. Plasma exposure increased the phosphorylation of ERK and JNK at 30min after the exposure, but the phosphorylation of both was decreased to less than control levels at 1 and 4h after the exposure. Plasma exposure increased the percentage of cells in the G2/M phase at 8h after the exposure. In conclusion, plasma exposure retarded the proliferation of C2C12 myoblasts by G2/M arrest. Therefore, plasma exposure can be a possible treatment for the anti-proliferative effects of malignant tumors, such as RMS, without affecting differentiated skeletal muscle cells.

The synergistic effect of advanced oxidation processes to eliminate resistant chemical compounds

The aim of this work is the study of application of the synergistic effects of various advanced oxidation processes (AOPs) in waste water treatment. Attention is paid to decomposition of chemical compounds resistant to biodegradation. These chemical compounds are commonly based on pharmaceutical products, pesticides, surfactants and dyes.In our contribution, the synergistic effect of simultaneously applied photocatalyst and low temperature atmospheric plasma or UV light on decomposition of model chemicals (Acid Orange 7, Hydrocortisone, Verapamil hydrochloride) was studied. TiO2 was used as the photocatalyst. Model chemicals with photocatalytic active TiO2 were exposed to atmospheric plasma discharge (Gliding Arc) or UV source in order to improve generation of active hydroxyl groups and oxidation processes. The relations between different effects of AOPs during chemicals decomposition process were analyzed.It was observed that decomposition of model chemicals is strongly improved by synergistic effect of: (i) photocatalytic reaction occurring on photocatalyst TiO2, (ii) presence of oxidative radicals, (iii) presence of wide-range UV.

Dose-dependent enhancement of bone marrow stromal cells adhesion, spreading and osteogenic differentiation on atmospheric plasma-treated poly(l-lactic acid) nanofibers

Although poly(l-lactic acid) nanofibers are known to promote osteogenic differentiation of bone marrow stromal cells, their relative hydrophobicity and surface inertia tend to hinder their biomedical application. We explored a feasible and effective technique to improve the bioactivity and biocompatibility of poly(l-lactic acid) fibers for further application in regenerative medicine. A low-temperature atmospheric plasma was used to treat poly(l-lactic acid) nanofibers for 1, 5, and 10 min, and the surface properties and dose-dependent effects on the behavior of bone marrow stromal cells were studied. Both the amino group content and surface hydrophilicity of the nanofibers increased with treatment time, whereas the spreading and proliferation of bone marrow stromal cells were greatest on nanofibers which had been treated for 5 min, followed by samples treated for 1 and 10 min. The quantitative reverse transcription–polymerase chain reaction analysis of the bone marrow stromal cells on the 5-min-treated nanofibers had the highest expression level of osteogenic marker genes including RUNX2, BMP2, ALP, COL1A1, OPN, and OCN. The nanofibers treated for 5 min also promoted the high levels of alkaline phosphatase activity. These results suggest the exertion of dose-dependent effects by atmospheric plasma treatment on the surface of poly(l-lactic acid) nanofibers, and that this treatment is a feasible and effective technique to improve biomaterial biocompatibility and promotion of osteogenic differentiation of bone marrow stromal cells.

Optical emission spectroscopy study in the VUV–VIS regimes of a developing low-temperature plasma in nitrogen gas

The mechanisms leading to the development of an atmospheric low temperature plasma along a surface under pulsed conditions is of current interest. In the early plasma phase, high energy photons are a contributing factor to the process of generating electron avalanches resulting in surface flashover. Since only photons in the vacuum ultraviolet (VUV) regime are energetic enough to cause step-ionization or direct ionization of atmospheric gases, an experiment has been set up to enable observations of photons with wavelengths shorter than 200 nm while still allowing observation up to 800 nm. A spectrum simulation software package has been developed to allow for temperature analysis on the developing plasma in the VUV region. Observations below 200 nm revealed a Boltzmann distributed excited state population corresponding to a temperature of 3.1 eV. Time-resolved emission spectroscopy measurements of the entire electrode region during the streamer phase of breakdown demonstrate the presence of molecular nitrogen emission lines from the second positive system. Further photomultiplier tube measurements of the spark phase showed a rapid decrease in intensity of the second positive system compared to that of a representative atomic emission line in the VUV regime. This emission dominates the ultraviolet–visible (UV–VIS) spectrum during the initial phases of breakdown with little detection of other sources of emission during this phase.

Low-temperature atmospheric plasma increases the expression of anti-aging genes of skin cells without causing cellular damages

Efforts to employ various types of plasma in the field of skin care have increased consistently because it can regulate many biochemical reactions that are normally unaffected by light-based therapy. One method for skin rejuvenation adopted a high-temperature plasma generator to remove skin epithelial cells. In this case, the catalyzing effects of the plasma were rarely used due to the high temperature. Hence, the benefits of the plasma were not magnified. Recently, many types of low-temperature plasma devices have been developed for medical applications but their detailed functions and working mechanisms are unclear. The present study examined the effect of low-temperature microwave plasma on skin cells. Treatment with low-temperature plasma increased the expression of anti-aging genes in skin cells, including collagen, fibronectin and vascular endothelial growth factor. Furthermore, the plasma treatment did not cause cell death, but only induced slight cell growth arrest at the G2 phase. Although the cells treated with low-temperature plasma showed moderate growth arrest, there were no signs of thermal or genetic damage of skin cells. Overall, this low-temperature microwave plasma device induces the expressions of some anti-aging-related genes in skin cells without causing damage.

Low-temperature atmospheric pressure argon plasma treatment and hybrid laser-plasma ablation of barite crown and heavy flint glass

We report on atmospheric pressure argon plasma-based surface treatment and hybrid laser-plasma ablation of barite crown glass N-BaK4 and heavy flint glass SF5. By pure plasma treatment, a significant surface smoothing, as well as an increase in both the surface energy and the strength of the investigated glass surfaces, was achieved. It was shown that for both glasses, hybrid laser plasma ablation allows an increase in the ablation depth by a factor of 2.1 with respect to pure laser ablation. The ablated volume was increased by an averaged factor of 1.5 for N-BaK4 and 3.7 for SF5.

Chaos in atmospheric-pressure plasma jets

We report detailed characterization of a low-temperature atmospheric-pressure plasma jet that exhibits regimes of periodic, quasi-periodic and chaotic behaviors. Power spectra, phase portraits, stroboscopic section and bifurcation diagram of the discharge current combine to comprehensively demonstrate the existence of chaos, and this evidence is strengthened with a nonlinear dynamics analysis using two control parameters that maps out periodic, period-multiplication, and chaotic regimes over a wide range of the input voltage and gas flow rate. In addition, optical emission signatures of excited plasma species are used as the second and independent observable to demonstrate the presence of chaos and period-doubling in both the concentrations and composition of plasma species, suggesting a similar array of periodic, quasi-periodic and chaotic regimes in plasma chemistry. The presence of quasi-periodic and chaotic regimes in structurally unbounded low-temperature atmospheric plasmas not only is important as a fundamental scientific topic but also has interesting implications for their numerous applications. Chaos may be undesirable for industrial applications where cycle-to-cycle reproducibility is important, yet for treatment of cell-containing materials including living tissues it may offer a novel route to combat some of the major challenges in medicine such as drug resistance. Chaos in low-temperature atmospheric plasmas and its effective control are likely to open up new vistas for medical technologies.

Atmospheric pressure argon plasma-assisted enhancement of laser ablation of aluminum

In this paper, we present a hybrid laser-plasma ablation method for material processing applications. For this purpose, a coaxial configuration consisting of a low-temperature atmospheric pressure argon plasma beam and a Nd:YAG-laser at a wavelength of 355 nm was used. Both pure laser ablation and hybrid laser-plasma ablation experiments were performed on aluminum at different laser energies and numbers of laser pulses. In the case of hybrid ablation, both the depth and volume ablation rates were increased significantly in comparison to pure laser ablation. This effect is described by a linear interrelationship of both the ablation rate and the particularly applied laser energy and is thus due to energetic synergies. Such behavior can be explained by the de-excitation of argon plasma species and an accompanying energy deposition at the generated debris and the sample surface. The energetic effect was found to abate with increasing ablation depth. However, considerable improvements in terms of ablation rate are achieved in the near-surface depth range of approx. 500 microns.

Study on an oxygen plasma treatment of a basalt fiber and its effect on the interlaminar fracture property of basalt/epoxy woven composites

In this study, the effects of surface treatment of a basalt fiber by low-temperature atmospheric oxygen plasma on the interlaminar fracture behavior of basalt/epoxy woven composites were investigated. A commercial basalt fiber and its woven fabric were treated by low-temperature atmospheric oxygen plasma. Contact angle was measured to examine the changes in wettability of the basalt fiber. The chemical and morphological changes were characterized by using XPS and FE-SEM. Basalt/epoxy woven composites were fabricated with and without oxygen plasma treatment, and their interlaminar fracture toughnesses were compared. The results showed that the wettability of the basalt fiber was remarkably increased, accompanied by physical etching and by the formation of chemical functional groups containing oxygen and nitrogen on the fiber surface. The interlaminar fracture toughness of basalt/epoxy woven composites was improved by 16% by oxygen plasma treatment. SEM results on the fractured surface exhibited epoxy resin adhered well around the basalt fibers of the oxygen plasma-treated specimen compared to that of the untreated specimen. An adhesive force between fiber/resin interfaces was improved by oxygen plasma treatment, and this increased the interlaminar fracture toughness of basalt/epoxy woven composites.