Direct and Indirect Bactericidal Effects of Cold Atmospheric-Pressure Microplasma and Plasma Jet

The direct and indirect bactericidal effects of dielectric barrier discharge (DBD) cold atmospheric-pressure microplasma in an air and plasma jet generated in an argon-oxygen gas mixture was investigated on Staphylococcus aureus and Cutibacterium acnes. An AC power supply was used to generate plasma at relatively low discharge voltages (0.9–2.4 kV) and frequency (27–30 kHz). Cultured bacteria were cultivated at a serial dilution of 10⁻⁵, then exposed to direct microplasma treatment and indirect treatment through plasma-activated water (PAW). The obtained results revealed that these methods of bacterial inactivation showed a 2 and 1 log reduction in the number of survived CFU/mL with direct treatment being the most effective means of treatment at just 3 min using air. UV–Vis spectroscopy confirmed that an increase in treatment time at 1.2% O₂, 98.8% Ar caused a decrease in O₂ concentration in the water as well as a decrease in absorbance of the peaks at 210 nm, which are attributed NO₂⁻ and NO₃⁻ concentration in the water, termed denitratification and denitritification in the treated water, respectively.     

Potential of Carvacrol and Thymol in Reducing Biofilm Formation on Technical Surfaces

Polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE), and stainless steel (SS) are commonly used in medicine and food production technologies. During contact with microorganisms on the surface of these materials, a microbial biofilm is formed. The biofilm structure is difficult to remove and promotes the development of pathogenic bacteria. For this reason, the inhibition of biofilm formation in medical and food production environments is very important. For this purpose, five naturally occurring compounds were used for antimicrobial screening tests. The two with the best antimicrobial properties were chosen to inhibit the biofilm formation of Staphylococcus aureus and Pseudomonas aeruginosa. After 3 days of exposure, thymol reduced the amount of biofilm of Pseudomonas aeruginosa within the range of 70–77% and 52–75% for Staphylococcus aureus. Carvacrol inhibited the formation of biofilms by up to 74–88% for Pseudomonas aeruginosa and up to 86–100% for Staphylococcus aureus. Those phenols decreased the enzyme activity of the biofilm by up to 40–100%. After 10 days of exposure to thymol, biofilm formation was reduced by 80–100% for Pseudomonas aeruginosa and by about 79–100% for Staphylococcus aureus. Carvacrol reduced the amount of biofilm by up to 91–100% for Pseudomonas aeruginosa and up to 95–100% for Staphylococcus aureus.     

Langmuir probe measurements during plasma-activated chemical vapor deposition in the system argon/oxygen/Aluminum isopropoxide

A Langmuir probe investigation of Ar/O₂/Al(OPr¹)₃ plasmas is described. The probe contamination depends on the probe position and the flow of tine carrier gases. Whereus far from the working gas inlet characteristics without any hysteresis were obtained, near to the inlet undisturbed characteristics were recorded only for small gas flows or a low vapor pressure of the precursor. Condensation of the precursor ai the probe surface prior to the plasma excitation was the main source of probe contamination. A decrease ire the plasma potential with respect to the ground observed during experiments was attributed to the formation of a dielectric film on the rf electrode. This resulted in a self-bias responsible for the decrease in plasma potential.     

Control of the Sorption Properties and Wettability of a Nonwoven Polypropylene Material by Direct Gas Fluorination

The effect of direct gas fluorination on the surface properties of a nonwoven polypropylene material was studied. Direct gas fluorination with mixtures of different compositions allows directional variation of the surface properties of the nonwoven polypropylene material. The surface becomes more hydrophobic when using a mixture of fluorine and nitrogen but less hydrophobic when using a mixture of fluorine, oxygen, and nitrogen. The modification leads to changes in the chemical composition of the surface and in the roughness of the material. The nonwoven polypropylene materials thus obtained exhibit increased sorption capacity for spent oil or water, respectively. Variation of the properties of the nonwoven polypropylene material allows expansion of its applications.

     

Deposition of Gold Nanoparticles on Polypropylene Nonwoven Pretreated by Dielectric Barrier Discharge and Diffuse Coplanar Surface Barrier Discharge

The aim of this study was to examine and compare the potentials of two different ambient air plasma treatments: volume dielectric barrier discharge and diffuse coplanar surface barrier discharge, for the activation of polypropylene (PP) nonwovens surface. This was done in order to enhance the deposition of gold nanoparticles (AuNPs) onto PP surface. AuNPs were attached onto PP surface from colloidal solution prepared without stabilizers. Scanning electron microscopy, atomic force microscopy, attenuated total reflection-Fourier transform infrared spectroscopy, water absorption, and AuNPs uptake were used to assess the surface changes due to the plasma treatment, and to evaluate the durability of the achieved treatment effects. Finally, as a very important aspiration of the research, antibacterial activity of AuNPs loaded PP nonwovens against pathogens Staphylococcus aureus and Escherichia coli was evaluated in vitro. The plasma modified PP nonwovens have highly improved wetting and sorption properties. The PP nonwovens loaded with 17–62 mg/kg AuNPs exhibit antibacterial activity against tested pathogens. Surprisingly, this activity was enhanced by the first sample rinsing.     

Water barrier characteristics of plasma polymers of perfluorocarbons

Perfluorocarbon monomers such as C₂F₄, C₂F₆, C₄F₁₀, and mixtures thereof with H₂, were subjected to plasma polymerization and deposited onto low-density polyethylene (LDPE) substrates. The effect of plasma conditions, surface characteristics, and surface dynamics of plasma polymers on their ability to improve the resistance to water vapor permeation was investigated. An optimum discharge energy density was found for a monomer which provided the greatest reduction water vapor permeability. Although all of the plasma polymers show higher hydrophobicity than polyethylene, the reduction in water vapor permeability is not uniquely related to water contact angle. The surface-dynamic stability of a plasma polymer surface was found to be the key factor in determining the barrier performance of the plasma polymer. The extent of change of surface-configuration after water immersion strongly correlated with the improvement in the water vapor permeation resistance. Plasma polymers with the higher surface-dynamic stability provided the better water barrier coating applied on LDPE films. © 1996 John Wiley & Sons, Inc.     

Characterization of a distributed plasma ionization source (DPIS) for ion mobility spectrometry and mass spectrometry

A recently developed atmospheric pressure ionization source, a distributed plasma ionization source (DPIS), was characterized and compared to commonly used atmospheric pressure ionization sources with both mass spectrometry (MS) and ion mobility spectrometry (IMS). The source consisted of two electrodes of different sizes separated by a thin dielectric. Application of a high RF voltage across the electrodes generated plasma in air yielding both positive and negative ions. These reactant ions subsequently ionized the analyte vapors. The reactant ions generated were similar to those created in a conventional point-to-plane corona discharge ion source. The positive reactant ions generated by the source were mass identified as being solvated protons of general formula (H₂O)_nH⁺ with (H₂O)₂H⁺ as the most abundant reactant ion. The negative reactant ions produced were mass identified primarily as CO₃⁻, NO₃⁻, NO₂⁻, O₃⁻ and O₂⁻ of various relative intensities. The predominant ion and relative ion ratios varied depending upon source construction and supporting gas flow rates. A few compounds including drugs, explosives and amines were selected to evaluate the new ionization source. The source was operated continuously for 3 months and although surface deterioration was observed visually, the source continued to produce ions at a rate similar that of the initial conditions.     

Decontamination-Induced Modification of Bioactivity in Essential Oil-Based Plasma Polymer Coatings

Plasma polymer coatings fabricated from Melaleuca alternifolia essential oil and its derivatives have been previously shown to reduce the extent of microbial adhesion on titanium, polymers, and other implantable materials used in dentistry. Previous studies have shown these coatings to maintain their performance under standard operating conditions; however, when used in e.g., a dental implant, these coatings may inadvertently become subject to in situ cleaning treatments, such as those using an atmospheric pressure plasma jet, a promising tool for the effective in situ removal of biofilms from tissues and implant surfaces. Here, we investigated the effect of such an exposure on the antimicrobial performance of the Melaleuca alternifolia polymer coating. It was found that direct exposure of the polymer coating surface to the jet for periods less than 60 s was sufficient to induce changes in its surface chemistry and topography, affecting its ability to retard subsequent microbial attachment. The exact effect of the jet exposure depended on the chemistry of the polymer coating, the length of plasma treatment, cell type, and incubation conditions. The change in the antimicrobial activity for polymer coatings fabricated at powers of 20–30 W was not statistically significant due to their limited baseline bioactivity. Interestingly, the bioactivity of polymer coatings fabricated at 10 and 15 W against Staphylococcus aureus cells was temporarily improved after the treatment, which could be attributed to the generation of loosely attached bioactive fragments on the treated surface, resulting in an increase in the dose of the bioactive agents being eluted by the surface. Attachment and proliferation of Pseudomonas aeruginosa cells and mixed cultures were less affected by changes in the bioactivity profile of the surface. The sensitivity of the cells to the change imparted by the jet treatment was also found to be dependent on their origin culture, with mature biofilm-derived P. aeruginosa bacterial cells showing a greater ability to colonize the surface when compared to its planktonic broth-grown counterpart. The presence of plasma-generated reactive oxygen and nitrogen species in the culture media was also found to enhance the bioactivity of polymer coatings fabricated at power levels of 10 and 15 W, due to a synergistic effect arising from simultaneous exposure of cells to reactive oxygen and nitrogen species (RONS) and eluted bioactive fragments. These results suggest that it is important to consider the possible implications of inadvertent changes in the properties and performance of plasma polymer coatings as a result of exposure to in situ decontamination, to both prevent suboptimal performance and to exploit possible synergies that may arise for some polymer coating-surface treatment combinations.     

Optical emission from tetrafluoromethane plasma and its relationship to surface modification of hexatriacontane

The optical emission from tetrafluoromethane plasma (2% argon included) has been studied by emission spectroscopy. The evolution ofCF ^*,CF ₂ ^* , andF emissions has been followed during the treatment of an organic surface. An-alkane, hexatriacontane, has been used as a model for high density polyethylene surface and treated in different plasma conditions. We found that the evolution of fluorinated species emissions in the plasma gas phase is not only a measurement of the reactive species concentrations, but also an indication of the surface modifications. The surface properties, such as surface energy and surface roughness are correlated to the emission intensity of reactives species in the plasma gas phase. A mild exposure to the plasma can result in a great decrease of surface energy corresponding to the fluorination. The surface roughness only changes under drastic plasma conditions.     

Influence of Atmospheric Pressure Non-thermal Plasma on Inactivation of Biofilm Cells

The objective of this study is to investigate the bactericidal efficiency of atmospheric pressure non-thermal (cold) dielectric barrier discharge plasma on biofilms of Staphylococcus aureus and Escherichia coli. In general, cold plasma is a mixture of electrons, ions, neutral atoms and molecules. The different particles in cold plasmas exhibit different energies, i.e. electrons are much more energetic than other particles. This feature of cold plasmas allows to produce chemically reactive species at near room temperature that can be used in biological applications. Bacteria inactivation was performed using the air direct plasma (with reactive species, UV light, excited species and electric fields). Discharge power density during the experiment was equal to 70 mW/cm² and plasma dose was regulated by the treatment time. Bacterial biofilms were treated with the non-thermal plasma for 10–300 s. The most effective reduction in the number of S. aureus cells was found after 300 s of treatment and was 2.77 log₁₀ that is 99.83%. When the biofilm of E. coli was used in the experiment, killing of bacteria was independent of the exposure time and the mortality of cells did not exceed 0.48 that is 66.7% kill. The lethal effect on E. coli and S. aureus cells were observed after 300 and 120 s of plasma treatment, respectively but it was necessary to remove the layers of dead cells. The proposed process of removing dead cell layers was carried out due to the probable shielding effect, i.e. dead cells prevent further penetration of active plasma species into the deeper layers of the biofilm. It was shown that the effectiveness of cell destruction by the non-thermal plasma depends on the thickness of biofilm.     

Investigation of Cold Atmospheric Plasma-Activated Water for the Dental Unit Waterline System Contamination and Safety Evaluation in Vitro

The disinfection of the inner surface of a medical device has long been a challenge for the central sterile supply departments. Dental unit waterline system (DUWLs) foster the attachment of microorganisms and development of biofilm, which lead to continuous contamination of the outlet water from dental units; this contamination may be responsible for a potential risk of infection due to the exposure of patients and medical staff. The present study investigated the disinfection effects of cold atmospheric plasma-activated water (CAPAW) on DUWLs using a model of 5-day-old Enterococcus faecalis biofilm. The results showed that the colony-forming unit was reduced from 10⁷ to 0 after 5 min of treatment. The physicochemical properties of CAPAW were evaluated, including the pH value, oxidation reduction potential, and NO radical. The results showed that the inactivation mechanisms were mainly triggered by the reactive oxygen/nitrogen species. Additionally, CAPAW had a metal corrosion rate same as that of deionized water. We conclude that CAPAW can be applied as an appropriate alternative disinfectant against biofilm contamination of DUWLs.     

Oxidative Conversion of PFC via Plasma Processing with Dielectric Barrier Discharges

Perfluorocompounds (PFCs) have been extensively used as plasma etching andchemical vapor deposition (CVD) gases for semiconductor manufacturingprocesses. PFCs have significant effects on the global warming and havevery long atmospheric lifetimes. Laboratory-scale experiments were performedto evaluate the effectiveness of CF4 conversion by using dielectric barrierdischarges (DBD). The results of this study revealed that the removalefficiency of CF₄ increased with application of higher voltage, gas residence time, oxygen content, and frequency. Combined plasma catalysis(CPC) is an innovative way for abatement of PFC and experimental results indicated that combining plasma with catalysts could effectively remove CF4. Products were analyzed by Fourier transform–infrared spectroscopy (FT–IR) and the major products of the CF4 processing with DBD were CO2, COF2, and CO, when O was included in the discharge process. Preliminary results indicated that as high as 65.9% of CF4 was decomposed with CPC operated at 15 kV, 240 Hz for the gas stream containing 300 ppmv CF₄,20% by volume O₂, and 40% by volume Ar, with N₂ as thecarrier gas.     

Surface hydrophilization for polypropylene microporous membranes: A facile interfacial crosslinking approach

A hydrophilic surface is very important for hydrophobic separation membranes such as polypropylene microporous membranes (PPMMs). In this work a facile and effective method, interfacial crosslinking combined with pretreatment by dielectric barrier discharge plasma at atmospheric pressure, was developed for endowing PPMMs with a hydrophilic and charged surface. Poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) and p-xylylene dichloride were selected for quaternization crosslinking to form a positively charged coating layer, which was characterized with FT-IR/ATR, XPS, and FESEM. Water contact angle and pure water flux measurements were conducted to evaluate the surface hydrophilicity. The influence of surface charges on protein filtration was also investigated. It is found that the mass gain of interfacial crosslinking increases almost linearly with increasing the PDMAEMA concentration from 0.5 to 10 g/L. The crosslinking degree is larger than 80% according to the XPS results, ensuring the stability of the crosslinking layer. The surface hydrophilicity is demonstrated by the sharp decrease of water contact angle from 145° to 20°. The pure water flux also increases 3 times under the optimized conditions. Furthermore, the results of protein filtration suggest that these highly hydrophilic and charged surfaces can effectively resist the fouling of proteins.     

Creatinine sorbents based on nonwoven polymeric materials modified with tetra(4-tert-butyl)phthalocyanine and zinc complex

The experimental results, which show the possibility of immobilization of tetra(4-tert-butyl)phthalocyanine complex and its zinc complex on the surface of nonwoven polypropylene and lavsan materials. The alkali etching method was used for activation of the polypropylene surface. It was shown that the modified polymeric materials possess sorption activity relative to creatinine.     

Cold Atmospheric Plasma Jet as a Possible Adjuvant Therapy for Periodontal Disease

Due to the limitations of traditional periodontal therapies, and reported cold atmospheric plasma anti-inflammatory/antimicrobial activities, plasma could be an adjuvant therapy to periodontitis. Porphyromonas gingivalis was grown in blood agar. Standardized suspensions were plated on blood agar and plasma-treated for planktonic growth. For biofilm, dual-species Streptococcus gordonii + P. gingivalis biofilm grew for 48 h and then was plasma-treated. XTT assay and CFU counting were performed. Cytotoxicity was accessed immediately or after 24 h. Plasma was applied for 1, 3, 5 or 7 min. In vivo: Thirty C57BI/6 mice were subject to experimental periodontitis for 11 days. Immediately after ligature removal, animals were plasma-treated for 5 min once—Group P1 (n = 10); twice (Day 11 and 13)—Group P2 (n = 10); or not treated—Group S (n = 10). Mice were euthanized on day 15. Histological and microtomography analyses were performed. Significance level was 5%. Halo diameter increased proportionally to time of exposure contrary to CFU/mL counting. Mean/SD of fibroblasts viability did not vary among the groups. Plasma was able to inhibit P. gingivalis in planktonic culture and biofilm in a cell-safe manner. Moreover, plasma treatment in vivo, for 5 min, tends to improve periodontal tissue recovery, proportionally to the number of plasma applications.     

Compact plasma source for removal of hydrocarbons for surface analysis

A low–energy, constricted‐anode Anders‐type plasma source was built and tested for the chemical removal of adventitious carbon on surfaces. Oxygen plasma, generated in the source, extends to the sample surface through an aperture in the anode. This plasma reacts with surface hydrocarbons and removes them in less than a minute without influencing the intrinsic surface stoichiometry of nonoxidizing samples such as minerals, glasses, and metal oxides. Adventitious carbon removal is critical for accurate binding energy determination and quantitative measurements in XPS and AES, particularly in multicomponent materials. We measure the plasma to be composed primarily of O⁺ and O₂⁺, with minor H⁺, H₂⁺, and O⁺⁺ components. Ion energy distributions were measured for O⁺ and O⁺⁺ and show all emitted ions have energies less than 50 eV, confirming chemical desorption as the primary removal mechanism. The plasma source, easily built ‘in house’, is compact and can be mounted on a 2.75‐in flange for in situ specimen cleaning prior to surface analysis. Copyright © 2009 John Wiley & Sons, Ltd.     

Cleaning of Silicon and Steel Surfaces Using Dielectric Barrier Discharges

The plasma-activated removal of oil from contaminated silicon substrates and galvanized steel sheets has been performed using dielectric barrier discharges (DBD) at atmospheric pressure. Removal rates were determined by ellipsometric measurement of the oil film thickness, using polished silicon as substrates. With galvanized steel sheets, qualitative and quantitative investigations were done using fluorescence microscopic characterization of theplasma-treated surfaces. Both the ellipsometric and the fluorescence microscopic measurements yield the dependence of the removal rate on treatment parameterssuch as plasma–gas composition and gas flow. The film thickness measurements were calibrated using quantitative IR spectroscopic measurements. It could be shown that the removal rate increases with increasing oxygen content in the process gas, static removal rates of 0.6 nm/s and 7 nm/s being obtainedin pure nitrogen and in pure oxygen, respectively. Fluorescence microscopic investigations showed that oil can be removed even from grooves in the galvanized steel sheets.     

Effect of different types of substrate surface treatments on the graphene device performance

Graphene–substrate interface is very crucial for analyzing graphene device performance. In this article, we have shown how the graphene device performance got affected because of different types of substrate surface treatment techniques used before graphene transfer. For fabrication of graphene devices, monolayer chemical vapor deposition (CVD) graphene was transferred onto SiO₂ grown thermally on Si substrate. Forming gas annealed SiO₂/Si shows better device performance as compared with as-grown SiO₂ on Si substrate. A further effect of oxygen plasma and argon plasma cleaning of SiO₂ surface before graphene transfer was investigated. Forming gas annealing improves the performance and plasma treatment degrade the graphene devices' performance.     

The Role of Dielectric Barrier Discharge Atmosphere and Physics on Polypropylene Surface Treatment

Dielectric barrier discharge (DBD) is the discharge involved in corona treatment, widely used in industry to increase the wettability or the adhesion of polymer films or fibers. Usually DBD's are filamentary discharges but recently a homogeneous glow DBD has been obtained. The aim of this paper is to compare polypropylene surface transformations realized with filamentary and glow DBD in different atmospheres (He, N₂, N₂ + O₂ mixtures) and to determine the relative influence of both the discharge regime and the gas nature, on the polypropylene surface transformations. From wettability and XPS results it is shown that the discharge regime can have a significant effect on the surface transformations, because it changes both the ratio of electrons to gas metastables, and the space distribution of the plasma active species. This last parameter is important at atmospheric pressure because the mean free paths are short (m). These two points explain why in He, polypropylene wettability increase is greater by a glow DBD than by a filamentary DBD. In N₂, no significant effect of the discharge regime is observed because electrons and metastables lead to the same active species throughout the gas bulk. The specificity of a DBD in N₂ atmosphere compared to an atmosphere containing oxygen is that it allows very extensive surface transformations and a greater increase of the polypropylene surface wettability. Indeed, even in low concentration and independently of the discharge regime, when O₂ is present in the plasma gas, it controls the surface chemistry and degradation occurs.     

Design and Operating Characteristics of a Simple and Reliable DBD Reactor for Use with Atmospheric Air

The paper reports on the construction and operating characteristics of a planar dielectric barrier discharge (DBD) plasma generator. The generator was powered from a commercial frequency inverter at 400 Hz through a high voltage transformer. It could be operated up to a specific energy density (power per gas flow) of 20 Wh/m³. The corresponding power density was about 0.5 W per cubic centimeter of discharge volume. Special emphasis was given to a simple and reliable construction, which was easy to assemble and is based on a new, nonexpensive barrier material with excellent electrical, mechanical, and thermal properties. The modular reactor design allows simple plasma power scale-up. The reactor works with undried ambient air without additional cooling. In the range up to 10 Wh/m³ the ozone generation from ambient air was directly proportional to the energy density at a rate of 60 g O₃ per kWh or 30 ppm/Wh/m³. Thus the generator can serve as an effective source for chemically active radicals in plasma gas cleaning applications.