One Atmosphere Uniform Glow Discharge Plasma Research Articles

Atmospheric Plasma Inactivation of Foodborne Pathogens on Fresh Produce Surfaces

A study was conducted to determine the effect of one atmosphere uniform glow discharge plasma (OAUGDP) on inactivation of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes on apples, cantaloupe, and lettuce, respectively. A five-strain mixture of cultured test organisms was washed, suspended in phosphate buffer, and spot inoculated onto produce (7 log CFU per sample). Samples were exposed inside a chamber affixed to the OAUGDP blower unit operated at a power of 9 kV and frequency of 6 kHz. This configuration allows the sample to be placed outside of the plasma generation unit while allowing airflow to carry the antimicrobial active species, including ozone and nitric oxide, onto the food sample. Cantaloupe and lettuce samples were exposed for 1, 3, and 5 min, while apple samples were exposed for 30 s, 1 min, and 2 min. After exposure, samples were pummeled in 0.1% peptone water–2% Tween 80, diluted, and plated in duplicate onto selective media and tryptic soy agar and incubated as follows: E. coli O157:H7 (modified eosin methylene blue) and Salmonella (xylose lysine tergitol-4) for 48 h at 37°C, and L. monocytogenes (modified Oxford medium) at 48 h for 32°C. E. coli O157: H7 populations were reduced by >1 log after 30-s and 1-min exposures and >2 log after a 2-min exposure. Salmonella populations were reduced by >2 log after 1 min. Three- and 5-min exposure times resulted in >3-log reduction. L. monocytogenes populations were reduced by 1 log after 1 min of exposure. Three- and 5-min exposure times resulted in >3- and >5-log reductions, respectively. This process has the capability of serving as a novel, nonthermal processing technology to be used for reducing microbial populations on produce surfaces.

The One Atmosphere Uniform Glow Discharge Plasma (OAUGDP)—A Platform Technology for the 21st Century

Representatives from many industrial sectors are searching for more economic and ecologically sound technologies to meet regulatory and competitive pressures. Currently, the majority of industrial plasma processing is done with glow discharges at pressures below 10 torr. This tends to limit such applications to high-value items, as a result of the high capital cost of vacuum systems and the production constraints of batch processing. It has long been recognized that glow discharges would play a much larger industrial role if they could be generated at one atmosphere and in ambient air. A promising platform technology for plasma processing across many industrial sectors is the one atmosphere uniform glow discharge plasma (OAUGDP), a nonthermal normal glow discharge that operates in air (and other gases) at room temperature and atmospheric pressure. It generates active species useful for the sterilization, decontamination, and surface energy enhancement of films, fabrics, air filters, metals, and 3-D workpieces. This paper will survey exploratory research and development at the University of Tennessee's Plasma Sciences Laboratory on eight potential industrial applications of the OAUGDP that can be conducted at one atmosphere and at room temperature with air as the working gas

Inactivation of Foodborne Pathogens Using A One Atmosphere Uniform Glow Discharge Plasma

This study was conducted to determine the efficacy of a one atmosphere uniform glow discharge plasma (OAUGDP) for inactivation of foodborne pathogens and to evaluate the influence of growth temperature, pH, and culture age on their inactivation. Escherichia coli O157:H7, Listeria monocytogenes, Staphylococcus aureus, Bacillus cereus, Salmonella Enteritidis, Vibrio parahaemolyticus, Yersinia enterocolitica, and Shigella flexneri were evaluated. Three-strain mixtures of each bacterium were inoculated (6-7 log CFU/cm(2)) onto microscope slides containing nonselective agar media adjusted to pH 5 or 7. Samples were exposed to plasma for 0-240 sec immediately, or after incubation for 24 h at 10 degrees C or 35 degrees C. After exposure, the agar was removed from the slides and pummeled in 0.1% peptone water with a stomacher, serially diluted, surface plated onto nonselective media, and incubated at 35 degrees C. Exposure time, pH, incubation temperature, and culture age affected survival of all pathogens exposed to plasma (P < 0.05). The greatest reduction of pathogens generally occurred during the initial exposure time of 30 or 90 sec. Pathogens incubated for 24 h before exposure were more resistant than those exposed immediately after inoculation. Incubation at 35 degrees C before exposure resulted in greater resistance to plasma inactivation than incubation at 10 degrees C. No appreciable differences between gram-positive and gram-negative pathogens were observed, although the spore-forming B. cereus was more resistant to plasma than non-spore-formers. These findings support the potential for plasma treatment of foods or surfaces for pathogen reduction. Increased sensitivity of pathogens to plasma at reduced pH and temperature is encouraging, since these conditions are applicable to many foods during processing, handling, and storage.

PSpice simulation of one atmosphere uniform glow discharge plasma (OAUGDP) reactor systems

The PSpice software has been used to simulate the electrical characteristics of a one atmosphere uniform glow discharge plasma (OAUGDP) reactor system. An OAUGDP reactor system normally includes a power supply, a transformer, an impedance matching network, and the plasma reactor. The principal task in simulation is to develop a comprehensive PSpice model for the plasma discharge in an OAUGDP reactor, which may consist either of two parallel electrode plates with a small gap between them, or a planar plasma layer generated by coplanar parallel electrode strips. In an OAUGDP, at least one electrode is covered with a dielectric, which can be modeled as a capacitor, as can the gap containing the plasma. The plasma discharge itself is modeled as a voltage-controlled current source that is switched on when the voltage across the gap exceeds the plasma initiation voltage. The current source and its output current follow a power law of the applied voltage, an observed phenomenological characteristic of the voltage-current behavior of normal glow discharges. Simulation results agree well with experimental data from actual reactors. It has been found that in different operating regimes, the discharge current of the OAUGDP is described by voltage power laws with different exponents, and that the capacitance of the impedance matching network affects the shape of the modeled discharge current waveform in a manner consistent with experiment.

Impedance matching for one atmosphere uniform glow discharge plasma (OAUGDP) reactors

A characteristic one atmosphere uniform glow discharge plasma (OAUGDP) reactor requires a power supply capable of delivering a few kilowatts at a frequency of 1-10 kHz, and an rms voltage up to 20 kV. The OAUGDP reactor with the plasma energized can be modeled as a capacitor in parallel with a resistor. In addition, the nonideality of the transformer between the radio frequency (RF) power supply and the plasma reactor introduces an imaginary component in its impedance. Thus, the load of the RF power supply, as seen by its output terminals, is highly reactive. An impedance mismatch resulting from the absence of a matching network will cause a large reflected power from the plasma reactor back to the power supply that does not contribute to plasma formation, but requires an expensive overrated power supply. All the impedance matching networks in the existing literature are for the RF or microwave plasma applications under low pressures, and they cannot be applied to the applications of the OAUGDP, which is operated at much lower frequencies and much higher voltages. In this paper, the design theory and experimental results of two types of impedance matching circuits that match OAUGDP reactors to their power supplies will be presented.

Increasing the Surface Energy and Sterilization of Nonwoven Fabrics by Exposure to a One Atmosphere Uniform Glow Discharge Plasma (OAUGDP)*

A technique for generating active species with the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP) has been developed and used to sterilize and increase the surface energy, wettability and wickability of nonwoven fabrics. The OAUGDP is a non-thermal, fourth-state-of-matter plasma with the classical characteristics of a low pressure DC normal glow discharge that operates in air (and other gases) at atmospheric pressure. No vacuum system or batch processing is necessary, and a wide range of applications to fabrics and polymeric webs can be accommodated in a parallel plate plasma reactor. In addition to directly exposing webs and workpieces to active species for surface energy increase in a parallel-plate reactor, we have shown that active species capable of sterilization can be convected at near room temperature to a remote exposure chamber. This technology is simple, produces many effects that can be obtained in no other way, generates minimal pollutants or unwanted byproducts, and is suitable for online treatment of webs, films, and fabrics. Early exposures of nonwoven fabrics to the OAUGDP required minutes to produce relatively small increases of surface energy. These durations appeared too long for commercial application to fast-moving webs. Recent improvements in OAUGDP power density, plasma quality and impedance matching of the power supply to the parallel plate plasma reactor have made it possible to raise the surface energy of a variety of polymeric webs (PP, PET, PE, etc.) to levels in the range of 60 to 70 dynes/cm with one second of exposure. In most cases these high surface energies were not durable, and fell off to 50 dynes/cm after periods of weeks to months. Here, we report the exposure of nonwoven fabrics made of PP and PET at the UTK Textiles and Nonwovens Development Center (TANDEC) to an impedance matched parallel plate OAUGDP for durations ranging from one second to several tens of seconds. Data will be reported on the surface energy, wettability and wickability as functions of time of exposure, and of the aging effect after exposure. We will report the use of a OAUGDP with air as the working gas to sterilize a broad range of microorganisms on a variety of surfaces, and in several distinct applications. These include a Remote Exposure Reactor to sterilize large workpieces 20 centimeters or more from the plasma-generating region, and a sterilizable air filter.

Sterilization and plasma processing of room temperature surfaces with a one atmosphere uniform glow discharge plasma (OAUGDP)

A technique for generating active species with the one atmosphere uniform glow discharge plasma (OAUGDP) has been developed and tested in a wide range of potential plasma processing applications, including the sterilization and decontamination of surfaces. The OAUGDP is a non-thermal plasma with the classical characteristics of a low pressure DC normal glow discharge that operates in air (and other gases) at atmospheric pressure. In addition to directly exposing webs and workpieces to active species by immersion or at the plasma boundary of a parallel-plate reactor, we have shown that active species capable of sterilization can be convected at near room temperature to a remote exposure chamber. No vacuum system or batch processing is necessary, and a wide range of applications can be accommodated. This technology is simple, cost-effective and suitable for online treatment of webs and such three-dimensional workpieces as medical instruments. We will report the use of an air OAUGDP to sterilize a broad range of microorganisms on a variety of surfaces, and in several distinct applications. These include a remote exposure reactor to sterilize large workpieces 20 cm or more from the plasma-generating region, and a sterilizable air filter.

Air filter sterilization using a one atmosphere uniform glow discharge plasma (the volfilter)

Two characteristics of microorganisms-extremely small size (0.01 to a few micrometers) and the ability to reproduce-hinder the effective filtration of bacteria and viruses from indoor air. The microorganisms captured by a filter in spite of their small size can reproduce in situ and be released into the airstream, giving rise to the sick building syndrome. The application of the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP) to a filter can address both these issues. At University of Tennessee at Knoxville, we have recently developed the Volfilter, a planar version of the OAUGDP produced by attaching strip electrodes to both sides of a sheet of dielectric filter material and energizing the electrodes with a high-voltage, low-frequency RF source. After the filter material removes microorganisms from the airstream, the OAUGD plasma kills the captured microorganisms. The combination of an appropriate filter material and periodic application of the OAUGDP results in an effective capture and sterilization device even for the smallest microorganisms and requires minimum maintenance. This paper will describe results obtained during the operation of a laboratory-scale Volfilter challenged by two kinds of microorganisms, S. aureus and the bacterial virus Phi X 174. An objective of this work is to demonstrate that a Volfilter exposed to a OAUGDP will have the number of captured microorganisms on its surface reduced by a factor of one million.

An overview of research using the one atmosphere uniform glow discharge plasma (OAUGDP) for sterilization of surfaces and materials

The medical, food processing, and heating, ventilating, and air conditioning industries are searching for improved pasteurization, disinfection, and sterilization technologies. Candidate techniques must deal with and overcome such problems as thermal sensitivity and destruction by heat, formation of toxic by-products, costs, and inefficiency in performance. We report the results of a plasma source, the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP), which operates at atmospheric pressure in air and produces antimicrobial active species at room temperature, OAUGDP exposures have reduced log numbers of Gram negative and Gram positive bacteria, bacterial endospores, yeast, and bacterial viruses on a variety of surfaces. The nature of the surface influenced the degree of lethality, with microorganisms on polypropylene being most sensitive, followed by glass, and cells embedded in agar. Experimental results showed at least a 5 log/sub 10/ CFU reduction in bacteria within a range of 50-90 s of exposure. After 10-25 s of exposure, macromolecular leakage and bacterial fragmentation were observed. Vulnerability of cell membranes to reactive oxygen species (ROC) is hypothesized. Results from several novel OAUGDP configurations are presented, including a remote exposure reactor (RER) which uses transported active species to sterilize material located more than 20 cm from the plasma generation site, and a second planar electrode configuration developed for air filter sterilization. Applications of these technologies to the healthcare industry, the food industry, and decontaminating surfaces compromised by biological warfare agents are discussed.

A remote exposure reactor (RER) for plasma processing and sterilization by plasma active species at one atmosphere

We have developed a remote exposure reactor (RER) in which the active species of air and other gases responsible for sterilization and processing effects are generated on flat panels in a surface layer of one atmosphere uniform glow discharge plasma (OAUGDP). These active species are convected by forced airflow at one atmosphere and near room temperature to a remote exposure chamber in which the workpiece is located. This allows workpieces of any size or shape to be sterilized or processed without direct contact with the plasma. Here, we report operation of the RER as a sterilizer with both single-pass and recirculating active species flow through the remote exposure chamber. We used the RER to reduce the numbers of two genera of microorganisms (Esherichia coli and Staphylococcus aureus) on test samples of polypropylene fabric. When the recirculating airflow configuration was employed, the population both of E. coli and S. aureas cells was reduced by at least five decades after only 25 s of exposure. Tests in the single pass airflow configuration produced similar results, with the E. coli and S. aureas populations decreased by at least four decades after 25 s of exposure.

Use of a one atmosphere uniform glow discharge plasma to kill a broad spectrum of microorganisms

The medical, industrial, and food processing industries are constantly in search of new technologies to provide improved methods of sterilization and pasteurization. Proposed techniques must deal with such problems as thermal sensitivity and destruction by heat, formation of toxic by-products, cost, and inefficiency in performance. We report results from a newly invented plasma source, a one atmosphere uniform glow discharge plasma (OAUGDP), which is capable of operating at atmospheric pressure in air and providing antimicrobial active species at room temperature. OAUGDP exposures have reduced log numbers of bacteria (Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa), bacterial endospores (Bacillus subtilis and Bacillus pumilus), and various yeast and bacterial viruses on a variety of surfaces. These surfaces included polypropylene, filter paper, paper strips, solid culture media, and glass. Experimental results showed at least a ⩾5 log10 colony forming units (CFU) reduction in bacteria within a range of 15–90 s of exposure, whether the samples were exposed in conventional sterilization bags or exposed directly to the plasma. An exception to these very short exposure times were experiments with solid culture media in which 5 min of plasma exposure was necessary to produce ⩾5 log10 CFU reduction in bacterial counts. The effects of plasma treatment on bacterial cell structures were investigated by exposing cells to plasma for various durations and examining them by transmission electron microscopy. The results showed that cell breakage (lysis) occurred with the release of cellular contents. These data were consistent with spectrophotometric results in which the release of cellular constituents was measured as a change in ultraviolet absorption at 260 nm. With all microorganisms tested, a biphasic survival curve (logarithmic number of survivors versus time) was observed in plots of dose-response data. Differences in susceptibilities of microorganisms observed on various surfaces suggested that the degree of lethality was dependent upon the time of diffusion of active species through the medium to the organism and the makeup of the microbial cellular surface.

Room temperature sterilization of surfaces and fabrics with a one atmosphere uniform glow discharge plasma.

We report the results of an interdisciplinary collaboration formed to assess the sterilizing capabilities of the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP). This newly-invented source of glow discharge plasma (the fourth state of matter) is capable of operating at atmospheric pressure in air and other gases, and of providing antimicrobial active species to surfaces and workpieces at room temperature as judged by viable plate counts. OAUGDP exposures have reduced log numbers of bacteria, Staphylococcus aureus and Escherichia coli, and endospores from Bacillus stearothermophilus and Bacillus subtilis on seeded solid surfaces, fabrics, filter paper, and powdered culture media at room temperature. Initial experimental data showed a two-log10 CFU reduction of bacteria when 2 x 10(2) cells were seeded on filter paper. Results showed > or = 3 log10 CFU reduction when polypropylene samples seeded with E. coli (5 x 10(4)) were exposed, while a 30 s exposure time was required for similar killing with S. aureus-seeded polypropylene samples. The exposure times required to effect > or = 6 log10 CFU reduction of E. coli and S. aureus on polypropylene samples were no longer than 30 s. Experiments with seeded samples in sealed commercial sterilization bags showed little or no differences in exposure times compared to unwrapped samples. Plasma exposure times of less than 5 min generated > or = 5 log10 CFU reduction of commercially prepared Bacillus subtilis spores (1 x 10(5)); 7 min OAUGDP exposures were required to generate a > or = 3 log10 CFU reduction for Bacillus stearothermophilus spores. For all microorganisms tested, a biphasic curve was generated when the number of survivors vs time was plotted in dose-response cures. Several proposed mechanisms of killing at room temperature by the OAUGDP are discussed.

1166. To the problem of dielectric relaxation in two-layer dielectric SiO 2TiO 2: S A Akulinin et al,coll of papers on semicond materials, dev and their applic, Voronezh 1973, 8–11 ( in Russian)

A technique for generating active species with the one atmosphere uniform glow discharge plasma (OAUGDP) has been developed and tested in a wide range of potential plasma processing applications, including the sterilization and decontamination of surfaces. The OAUGDP is a non-thermal plasma with the classical characteristics of a low pressure DC normal glow discharge that operates in air (and other gases) at atmospheric pressure. In addition to directly exposing webs and workpieces to active species by immersion or at the plasma boundary of a parallel-plate reactor, we have shown that active species capable of sterilization can be convected at near room temperature to a remote exposure chamber. No vacuum system or batch processing is necessary, and a wide range of applications can be accommodated. This technology is simple, cost-effective and suitable for online treatment of webs and such three-dimensional workpieces as medical instruments. We will report the use of an air OAUGDP to sterilize a broad range of microorganisms on a variety of surfaces, and in several distinct applications. These include a remote exposure reactor to sterilize large workpieces 20 cm or more from the plasma-generating region, and a sterilizable air filter.