Valentin Pohoata

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.

Application of Emissive Probes for Plasma Potential Measurements in Fusion Devices

In experimental fusion devices, up to now, only cold probes were used to determine the plasma potential in the scrape-off layer (SOL), and their floating potential was assumed to be proportional to the plasma potential. However, drifting electrons or beams shift the current-voltage characteristic of a cold probe by a voltage, which corresponds to the mean kinetic energy of the drifting electrons. This problem can be avoided by the use of electron emissive probes, since an electron emission current is independent of electron drifts in the surrounding plasma. In addition emissive probes are insensitive to electron temperature fluctuations in the plasma. We have used an arrangement of three emissive probes in the edge plasma region of ISTTOK (Instituto Superior Tecnico tokamak) at Lisbon. The probes have been mounted in such a way that the tips are positioned on the same poloidal meridian but on different minor radii in the SOL. With this arrangement, the plasma potential has been measured in the edge region of the ISTTOK, and first results are presented in this contribution.

Influence of operational parameters on plasma polymerization process at atmospheric pressure

In this paper, a dielectric barrier discharge working at atmospheric pressure has been used in order to investigate the plasma polymerization reactions using styrene vapors. The macroscopic parameters were carefully chosen in order to obtain polymer thin films with high deposition rate and high concentration of activated species consequently. Thus, the plasma polymerization processes can be described considering the dependence of polymer deposition rate by monomer flow rate and discharge power. The domains of plasma polymerization reactions were identified and the optimum operating conditions were obtained at a maximum deposition rate of 3.8 nm/s (discharge power: 7.5 W). Different techniques of analysis were used to identify the chemical composition of plasma polystyrene films and the domains of polymerization reaction. The film thickness was measured by optical interferometry and the chemical composition was analyzed by Fourier-transform infrared spectroscopy, UV spectroscopy, and x-ray photoelectron sp...

Atmospheric pressure plasma jet—Living tissue interface: Electrical, optical, and spectral characterization

The atmospheric pressure plasma jet is studied as potential plasma source for medical applications in direct contact with living tissues. Plasma bullets are generated in the region of the high voltage electrode and propagate towards the tissue surface. The presence of a localized plasma structure on tissues, played here by a human fingertip, is experimentally revealed. It was found that this plasma structure is sustained by a current flowing through the tissue, with the magnitude dependent on the distance from the discharge tube. The characteristic time span of the plasma at the interface is up to 20 μs and the diameter up to 5 mm. These parameters were studied using the two independent techniques: ultra-fast imaging and photomultiplier measurements. Generation of supplementary reactive species at the interface, the NO molecules, was proved by optical emission spectroscopy.The atmospheric pressure plasma jet is studied as potential plasma source for medical applications in direct contact with living tissues. Plasma bullets are generated in the region of the high voltage electrode and propagate towards the tissue surface. The presence of a localized plasma structure on tissues, played here by a human fingertip, is experimentally revealed. It was found that this plasma structure is sustained by a current flowing through the tissue, with the magnitude dependent on the distance from the discharge tube. The characteristic time span of the plasma at the interface is up to 20 μs and the diameter up to 5 mm. These parameters were studied using the two independent techniques: ultra-fast imaging and photomultiplier measurements. Generation of supplementary reactive species at the interface, the NO molecules, was proved by optical emission spectroscopy.

Properties of some azo-copolyimide thin films used in the formation of photoinduced surface relief gratings

Thin free standing films have been obtained by casting from dimethylacetamide solutions of some azo-copolyimides. The dynamo-mechanical and dielectric properties, and the effect of the chemical structure of polymers on the physical properties are investigated. The incorporation of substituted azobenzene groups and hexafluoroisopropylidene units in the macromolecular chain allowed the patterning of the materials under different irradiation conditions. The azo-copolyimide thin films showed high thermal stability, low dielectric constant, good dynamo-mechanical characteristics and uniform surface relief gratings.

Atmospheric pressure plasma polymers for tuned QCM detection of protein adhesion.

Our efforts have been concentrated in preparing plasma polymeric thin layers at atmospheric pressure grown on Quartz Crystal Microbalance-QCM electrodes for which the non-specific absorption of proteins can be efficiently modulated, tuned and used for QCM biosensing and quantification. Plasma polymerization reaction at atmospheric pressure has been used as a simple and viable method for the preparation of QCM bioactive surfaces, featuring variable protein binding properties. Polyethyleneglycol (ppEG), polystyrene (ppST) and poly(ethyleneglycol-styrene) (ppST-EG) thin-layers have been grown on QCM electrodes. These layers were characterized by Atomic Force Microscopy (AFM), Contact angle measurements, Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The plasma ppST QCM electrodes present a higher adsorption of Concanavalin A (ConA) and Bovine Serum Albumin (BSA) proteins when compared with the commercial coated polystyrene (ppST) ones. The minimum adsorption was found for ppEG, surface, known by their protein anti-fouling properties. The amount of adsorbed proteins can be tuned by the introduction of PEG precursors in the plasma discharge during the preparation of ppST polymers.

Thermal behavior of bovine serum albumin after exposure to barrier discharge helium plasma jet

Non-thermal plasma jets at atmospheric pressure are useful tools nowadays in plasma medicine. Various applications are tested such as cauterization, coagulation, wound healing, natural and artificial surfaces decontamination, and sterilization. In order to know more about the effects of gas plasma on biological supramolecules, we exposed protein powders to a barrier discharge helium plasma jet. Then, spectroscopic investigations were carried out in order to obtain information on protein secondary, tertiary, and quaternary structures. We obtained a reduction of the protein alpha-helix content after the plasma exposure and a different behavior, for both thermal denaturation/renaturation kinetics and thermal aggregation process.

Elastomeric azo-polyurethanes containing fluorescent pyrene and their photo activity

Two bichromophoric polyetherurethanes with a small number of pyrene rings on the quaternary ammonium groups and photoisomerizable azobenzene chromophore attached to the soft (AzPUC-Py1) or hard segment (AzPUC-Py2) of the polymeric backbone were synthesized and characterized. The effect of polymer structure on the trans–cis and cis–trans photo(thermo)isomerization of azobenzene in thin films induced by UV light (λ = 365 nm) was investigated using UV spectroscopy, and in every case the quality of sensitizer of the pyrene was not evidenced. Moreover, a better photochromic response in the film containing azobenzene in the polyether component compared to that induced of the same chromophore in the hard segment was registered. Properties in the solution and thin films were then examined in relation with the fluorescence of pyrene molecule excited at λ exc = 335 nm. Results of the fluorescence study accompanied of a fluorescence quenching through N,N-diethylaniline (DEA) sustain that these polymers could be used for the detection of amines up to a concentration of 1.57 × 10−3 mol/l (AzPUC-Py1) and 3.14 × 10−3 mol/l (AzPUC-Py2), respectively, in DMF solution. Compared to the polymer solution, in the polymer film exposed to DEA-saturated vapors about 30% monomer fluorescence quenching was found after 90 min.

Modification of Polymer Blends Properties by Plasma/Electron Beam Treatment. I. Plasma Diagnosis and Bulk Properties of Plasma Treated Blends

Films of isotactic polypropylene/epoxy modified lignin have been plasma and electron beam treated, in order to improve the surface properties and their response to environmental factors. The optimal conditions for the treatment have been established by a detailed plasma diagnosis. The effect of the treatment on the films has been followed by: IR-spectroscopy, X-ray diffraction and differential scanning calorimetry. All results have been comparatively discussed with those corresponding to the untreated samples. It has been established that plasma and electron beam treatments are very efficient in imparting a high polarity and an increased hydrophylicity to the polyolefin-based blends.

Poly (Ethylene Glycol-Co-Styrene) Films Deposited by Plasma Polymerization Reactions at Atmospheric Pressure

Atmospheric pressure plasma co-polymerization of ethylene glycol and styrene was applied to produce poly (ethylene glycol-co-styrene) using a dielectric barrier discharge. The chemical structure of polymerized films was studied by Fourier-transform infrared spectroscopy which confirms that we obtained copolymerized films with hydroxyl groups incorporated. Chemical composition of films was studied by X-ray Photoelectron Spectroscopy and oxygen containing groups (C-O and C=O) were identified. Topography of polymer films was revealed using Atomic Force Microscopy technique and the film root mean square roughness (Rrms) was found to be 1.6 nm. Surface wettability was analyzed using water contact angle technique.