Abdel-Aleam H. Mohamed

Cold atmospheric pressure air plasma jet for medical applications

By flowing atmospheric pressure air through a direct current powered microhollow cathode discharge, we were able to generate a 2cm long plasma jet. With increasing flow rate, the flow becomes turbulent and temperatures of the jet are reduced to values close to room temperature. Utilizing the jet, yeast grown on agar can be eradicated with a treatment of only a few seconds. Conversely, animal studies show no skin damage even with exposures ten times longer than needed for pathogen extermination. This cold plasma jet provides an effective mode of treatment for yeast infections of the skin.

Direct current glow discharges in atmospheric air

A microhollow cathode discharge was used as plasma cathode to sustain a stable direct current glow discharge in atmospheric pressure air. The length of the glow discharge column was varied from 1 mm to 2 cm, with the sustaining voltage increasing linearly with length. For glow discharges with currents on the order of 10 mA, the electron density in the air plasmas exceeded 10/sup 11/ cm/sup -3/, with highest values of almost 10/sup 13/ cm/sup -3/ close to the plasma cathode. When two 8.5-mA discharges were operated in parallel, at a distance of 0.4 cm, the discharge plasmas were found to merge for electrode gaps exceeding 0.5 cm, an effect that can be used to generate large volume, homogenous air plasmas.

Removal of volatile organic compounds in atmospheric pressure air by means of direct current glow discharges

A nonthermal plasma with an electron density on the order of 10/sup 12/ cm/sup -3/ and a gas temperature of 2000 K was generated in atmospheric pressure air, using a microhollow cathode discharge as plasma cathode. The plasma was sustained in a /spl sim/1 mm/sup 3/ micro reactor, by a voltage of 470 V between the plasma cathode and a planar anode, and at currents ranging from 12 to 22 mA. This direct current glow discharge has been used to study the remediation of methane and benzene, two of the most stable volatile organic compounds (VOCs). The removal fraction for 300-ppm methane in atmospheric pressure air, flowing through the 0.5-mm thick plasma layer, with a residence time of the gas in the plasma of less than 0.5 ms, was measured at 80% with an energy density of 4 kJ/L. For benzene, the remediation rate is as high as 90%, comparable to results obtained with low pressure glow discharges. The energy efficiency for benzene remediation is 0.9 g/kWh, higher than that obtained for benzene remediation in low pressure glow discharges in noble gases. However, the VOC fraction remaining was found to be limited to values of approximately 0.1 and 0.05 for methane and benzene, respectively. In addition to experimental studies, the VOC dissociation mechanism in a VOC/dry air mixture plasma was modeled using a zero-dimensional plasma chemistry code. The modeling results have shown that atomic oxygen impact reactions are the dominant dissociation reactions for VOC destruction in this kind of glow discharge. Diffusion of atomic oxygen to the dielectric walls of the reactor is assumed to cause the observed limitation in the VOC destruction rate and efficiency.

Comparative Studies of Atmospheric Pressure Plasma Characteristics Between He and Ar Working Gases for Sterilization

Helium (He) and Argon (Ar) atmospheric pressure plasma jets operated with low-frequency power source are designed and studied. The current and voltage waveforms, formation of plasma jets, estimated rotational and vibrational temperatures, optical emission spectra, and numerical simulations for He and Ar gases are investigated to analyze the plasma characteristics. Ar plasma shows higher discharge current and many instantaneous current peaks compared with He plasma. For gas flow between 1 and 7 L/min and applied voltage between 3 and 10 kV, no significant changes in Ar plasma are observed. He plasma is found to be sensitive as far as gas flow rate and applied voltage are concerned. This sensitivity is associated with a transition from laminar to turbulent mode of gas flow. The estimated gas temperatures show higher values for Ar plasma than those of He plasma. Ar plasma jet emits extremely high intensity of OH (305 nm ~312 nm) and O (777 nm) compared with that emitted from He plasma jet. High concentration of OH and O in Ar plasma is related with high density of electrons with 4-5 eV, which is in the range of the dissociation energy of H-H, O-H, and O=O bonds. As a result, wider sterilization area and higher sterilization efficacy in indirect treatment are observed for Ar plasma than He plasma.

Inhibitory effect of double atmospheric pressure argon cold plasma on spores and mycotoxin production of Aspergillus niger contaminating date palm fruits

BACKGROUND Aspergillus niger has been reported as a potentially dangerous pathogen of date-palm fruits in Saudi Arabia due to the production of fumonisin B2 (FB2 ) and ochratoxin A (OTA). In a trial to disinfect this product, a double atmospheric pressure argon cold plasma (DAPACP) jet system was set up and evaluated against spore germination and mycotoxin production of the pathogen. RESULTS The plasma jets were characterised photographically, electrically and spectroscopically. DAPACP jet length increases with the increase of argon flow rate, with optimum rate at 3.5 L min(-1) . The viability of A. niger spores, inoculated onto sterilised date palm fruit discs, progressively decreases with extension of the exposure time of DAPACP due to the more quantitative amount of OH and O radicals interacting with the examined samples. There was a progressive reduction of the amount of FB2 and OTA detected in date palm discs on extension of the exposure time of the plasma-treated inoculums at flow rate of 3.5 L min(-1) . FB2 was not detected in the discs inoculated with 6-min plasma-treated A. niger, while OTA was completely absent when the fungus was treated for 7.5 min. CONCLUSION DAPACP showed promising results in dry fruit decontamination and in inhibition of mycotoxin release by A. niger contaminating the fruits. The progress in the commercial application of cold plasma needs further investigation concerning the ideal width of the plasma output to enable it to cover wider surfaces of the sample and consequently inducing greater plasma performance.

Inhibitory effect of silver nanoparticles mediated by atmospheric pressure air cold plasma jet against dermatophyte fungi.

In an in vitro study with five clinical isolates of dermatophytes, the MIC(50) and MIC(100) values of silver nanoparticles (AgNPs) ranged from 5 to 16 and from 15 to 32 μg ml(- 1), respectively. The combined treatment of AgNPs with atmospheric pressure-air cold plasma (APACP) induced a drop in the MIC(50) and MIC100 values of AgNPs reaching 3-11 and 12-23 μg ml(- 1), respectively, according to the examined species. Epidermophyton floccosum was the most sensitive fungus to AgNPs, while Trichophyton rubrum was the most tolerant. AgNPs induced significant reduction in keratinase activity and an increase in the mycelium permeability that was greater when applied combined with plasma treatment. Scanning electron microscopy showed electroporation of the cell walls and the accumulation of AgNPs on the cell wall and inside the cells, particularly when AgNPs were combined with APACP treatment. An in vivo experiment with dermatophyte-inoculated guinea pigs indicated that the application of AgNPs combined with APACP was more efficacious in healing and suppressing disease symptoms of skin as compared with the application of AgNPs alone. The recovery from the infection reached 91.7 % in the case of Microsporum canis-inoculated guinea pigs treated with 13 μg ml(- 1) AgNPs combined with APACP treatment delivered for 2  min. The emission spectra indicated that the efficacy of APACP was mainly due to generation of NO radicals and excited nitrogen molecules. These reactive species interact and block the activity of the fungal spores in vitro and in the skin lesions of the guinea pigs. The results achieved are promising compared with fluconazole as reference antifungal drug.

Modeling of Nanoparticle-Mediated Electric Field Enhancement Inside Biological Cells Exposed to AC Electric Fields

We present in this article the effect of alternating electric field at kilohertz (kHz) and megahertz (MHz) frequencies on the biological cells in presence and absence of nanoparticles. The induced electric field strength distribution in the region around cell membrane and nucleus envelope display different behavior at kHz and MHz frequencies. The attachment of gold nanoparticles (GNPs), especially gold nanowires around the surface of nucleus induce enhanced electric field strengths. The induced field strengths are dependent on the length of nanowire and create varying field regions when the length of nanowire is increased from 2 to 4 µm. The varying nanowire length increased the induced field strengths inside nucleoplasm and region adjacent to the nucleus in the cytoplasm. We investigated a process of electrostatic disruption of nucleus membrane when the induced electric field strength across the nucleus exceeds its tensile strength.

Deterioration to extinction of wastewater bacteria by non-thermal atmospheric pressure air plasma as assessed by 16S rDNA-DGGE fingerprinting

The use of cold plasma jets for inactivation of a variety of microorganisms has recently been evaluated via culture-based methods. Accordingly, elucidation of the role of cold plasma in decontamination would be inaccurate because most microbial populations within a system remain unexplored owing to the high amount of yet uncultured bacteria. The impact of cold atmospheric plasma on the bacterial community structure of wastewater from two different industries was investigated by metagenomic-based polymerase chain reaction-denaturing gradient gel electrophoresis (DGGE) utilizing 16S rRNA genes. Three doses of atmospheric pressure dielectric barrier discharge plasma were applied to wastewater samples on different time scales. DGGE revealed that the bacterial community gradually changed and overall abundance decreased to extinction upon plasma treatment. The bacterial community in food processing wastewater contained 11 key operational taxonomic units that remained almost completely unchanged when exposed to plasma irradiation at 75.5 mA for 30 or 60 s. However, when exposure time was extended to 90 s, only Escherichia coli, Coliforms, Aeromonas sp., Vibrio sp., and Pseudomonas putida survived. Only E. coli, Aeromonas sp., Vibrio sp., and P. putida survived treatment at 81.94 mA for 90 s. Conversely, all bacterial groups were completely eliminated by treatment at 85.34 mA for either 60 or 90 s. Dominant bacterial groups in leather processing wastewater also changed greatly upon exposure to plasma at 75.5 mA for 30 or 60 s, with Enterobacter aerogenes, Klebsiella sp., Pseudomonas stutzeri, and Acidithiobacillus ferrooxidans being sensitive to and eliminated from the community. At 90 s of exposure, all groups were affected except for Pseudomonas sp. and Citrobacter freundii. The same trend was observed for treatment at 81.94 mA. The variability in bacterial community response to different plasma treatment protocols revealed that plasma had a selective impact on bacterial community structure at lower doses and potential bactericidal effects at higher doses.

Correlation of Striated Discharge Patterns With Operating Conditions in Helium and Argon Atmospheric-Pressure Plasma Jets

This paper presents the evolution of striated discharge patterns in helium and argon atmospheric-pressure plasma jets as a function of gas flow rate and driving voltage. The striated patterns have been observed in helium and argon plasma jets at gas flow rates above 5 and 3 L/min, respectively. The striation patterns appear over the entire voltage range used for investigation (from 4 to 8 kV) in the helium plasma jet, whereas in the argon plasma jet, striation patterns appear over a limited voltage range (from 5.5 to 6.5 kV).

Generation of Large Volume Atmospheric Pressure Air Plasma

Atmospheric pressure large volume air plasma was generated by applying 100 ns, 1-kHz high voltage pulse between two parallel electrodes separated by 48-mm gap. The high voltage power electrode has uniformly distributed pens and ground electrode shaped as a flat disc. Glow discharge ignition is initialized at the outer pens to form luminousness circle. By applying higher voltage, the glow expands to ignite the internal pens and to fill the gap between the two electrodes. Each pen forms glow discharge plasma with the ground electrode. The increase in voltage or frequency enhances the plasma intensity and homogeneity. The generated plasma showed efficiency against the fruit borne fungi of grapes.