Radio-frequency oxygen plasma as a sterilization source (original) (raw)
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Low temperature atmospheric plasma for microbial decontamination
2013
Low temperature Plasma (LTP) is a high-energy gas that is created when an electrical current is passed through a gas. Until recently, plasmas could only be created at relatively high temperatures in a vacuum and the use of plasma on sensitive materials such as human tissue, food products, medical devices and the packaging industry, was therefore impractical. However, over the last few years technological breakthroughs have made it possible to produce low temperature plasmas under atmospheric conditions providing many advantages. Plasma discharges with a higher oxygen concentration have been associated with increased levels of microbial survival inhibition due to oxygen based active species, atomic oxygen and ozone. Low temperature plasmas have shown success in decontamination of a wide range of microorganisms including bacteria, fungi and algae and has even shown success in damaging bacterial spores. These factors have brought this exciting new, emerging technology to the forefront ...
Impact of low-temperature plasmas on Deinococcus radiodurans and biomolecules
The effects of cold plasma on Deinococcus radiodurans, plasmid DNA, and model proteins were assessed using microbiological, spectrometric, and biochemical techniques. In low power O2 plasma (25 W, ~45 mTorr, 90 min), D. radiodurans, a radiation-resistant bacterium, showed a 99.999% reduction in bioburden. In higher power O2 plasma (100 W and 500 mTorr), the reduction rate increased about 10-fold and observation by atomic force microscopy showed significant damage to the cell. Damage to cellular lipids, proteins, and chromosome was indicated by losses of infrared spectroscopic peaks at 2930, 1651, 1538, and 1245 cm-1, respectively. In vitro experiments show that O2 plasmas induce DNA strand scissions and cross-linking as well as reduction of enzyme activity. The observed degradation and removal of biomolecules was power-dependent. Exposures to 200 W at 500 mTorr removed biomolecules to below detection limits in 60 s. Emission spectroscopy indicated that D. radiodurans cells were volatilized into CO2, CO, N2, and H2O, confirming that these plasmas were removing complex biological matter from surfaces. A CO2 plasma was not as effective as the O2 plasma, indicating the importance of plasma composition and the dominant role of chemical degradation. Together, these findings have implications for NASA planetary protection schemes and for the contamination of Mars.
Analysis of emission data from O2 plasmas used for microbe sterilization
In order to study the sterilization capabilities of radio frequency driven low pressure oxygen plasmas, the radiative emission was recorded at various pressures and input powers. A distinct transition from the bright mode (primarily inductively coupled) to a dim mode (primarily capacitively coupled) was observed as the pressure was increased and/or the power decreased. The data was further analyzed to estimate the electron temperature, rotational and vibrational temperatures, and various species concentrations. Based on the diffusion and rovibrational relaxation times, it is concluded that the rotational temperatures can be assumed to be in equilibrium with the translational temperature. The ions are produced “hot” and have little time to get equilibrated with the translational temperature. It is further determined that in the bright mode, which is more effective in microbe sterilization, the translational/rotational temperatures are in the 650–850 K range, the electron temperatures are low (3.5–4.5 eV), and the concentrations of atomic O and atomic metastables are at 1 order of magnitude higher than in the dim mode.
Low temperature atmospheric pressure plasma sources for microbial decontamination
Journal of Physics D: Applied Physics, 2011
The aim of this article is to provide a survey of plasma sources at atmospheric pressure used for microbicidal treatment. In order to consider the interdisciplinary character of this topic an introduction and definition of basic terms and procedures is given for plasma as well as for microbicidal issues. The list of plasma sources makes no claim to be complete, but to represent the main principles of plasma generation at atmospheric pressure and to give an example of their microbicidal efficiency. The interpretation of the microbicidal results remain difficult due to the non standardized methods uses by different authors and due to the fact that small variations in the set up can change the results dramatically.
Inactivation of Bacteria and Biomolecules by Low-Pressure Plasma Discharges
Plasma Processes and Polymers, 2010
The inactivation of bacteria and biomolecules using plasma discharges were investigated within the European project BIODECON. The goal of the project was to identify and isolate inactivation mechanisms by combining dedicated beam experiments with especially designed plasma reactors. The plasma reactors are based on a fully computer-controlled, low-pressure inductively-coupled plasma (ICP). Four of these reactors were built and distributed among the consortium, thereby ensuring comparability of the results between the teams. Based on this combined effort, the role of UV light, of chemical sputtering (i.e. the combined impact of neutrals and ions), and of thermal effects on bacteria such as Bacillus atrophaeus, Aspergillus niger, as well as on biomolecules such as LPS, Lipid A, BSA and prions have been evaluated. The particle fluxes emerging from the plasmas are quantified by using mass spectrometry, Langmuir probe measurements, retarding field measurements and optical emission spectroscopy. The effects of the plasma on the biological systems are evaluated using atomic force microscopy, ellipsometry, electrophoresis, specially-designed western blot tests, and animal models. A quantitative analysis of the plasma discharges and the thorough study of their effect on biological systems led to the identification of the different mechanisms operating during the decontamination process. Our results confirm the role of UV in the 200-250 nm range for the inactivation of microorganisms and a large variability of results observed between different strains of the same species. Moreover, we also demonstrate the role of chemical sputtering corresponding to the synergism between ion bombardment of a surface with the simultaneous reaction of active species such as O, O 2 or H. Finally, we show that plasma processes can be efficient against different micro-organisms, bacteria and fungi, pyrogens, model proteins and prions. The effect of matrices is described, and consequences for any future industrial implementation are discussed.
Study of Oxygen Plasma for Application in Sterilization Processes
International Joint Conference on Biomedical Engineering Systems and Technologies, 2008
The main objective of this work was to propose a technique of sterilization for medical devices with less exposition time than current plasma techniques, and also determine if this technique can be applied to temperature sensitive materials. Therefore, it was used as biological sensor Bacillus subtilis spores var. niger ATCC 9372 and Bacillus stearothermophilus. For Bacillus subtilis indicators were used two substrates: glass with 2,0 x 107 CFU/substrate of microbial load initial, and paper strips with 3,8 x 10 6 CFU/ substrate of microbial load initial. The efficacy of process was evaluated with the count of survivors and it respective value of decimal reduction (D value). In this work it was used RIE (Reactive Ion Etching). For all processes were used Petri dishes with the sample in triplicates for both microorganisms types. The process parameters was varied as follow: gas flow -100, 200 and 500 sccm, pressure -100 and 330 mTorr, RF power -50, 100 and 150 Watts and the time were of 2 minutes up to 60 minutes. After these processes, we made the count of survivors, in order to evaluate the plasma efficiency as sterilizer agent. Espectrophotometric analysis was made to evaluate the oxygen consumption during all process, and was used a scanning electronic microscope to visualize the plasma effect over microorganisms. With these results it was possible to adapt the process parameters for each type of substrate.
International Journal of Design & Nature and Ecodynamics, 2021
Plasma process is a promising physical method for sterilization. Due to the lack of suitable plasma diagnostics, installed in the reactors, a general lack of knowledge happens about the gas-phase chemical composition and the influence of operating parameters. The same lack of knowledge happens in case of gas plasma generated from different gases, candidates for sterilization purposes. The aim of this work is to understand the role of different agents acting in the sterilization process, evaluate the effectiveness of different precursor gases and validate the plasma reactor dedicated. A plasma reactor, equipped with an extended set of plasma diagnostics is dedicated to the understanding the role of different agents of gas plasma sterilization process. A microbiological investigation is carried out to evaluate the efficiency of the steps of the process on cultures of Escherichia coli, using both hydrogen peroxide and argon. The effects on the colonies of Escherichia Coli are assessed ...
Low pressure plasma discharges for the sterilization and decontamination of surfaces
New Journal of Physics, 2009
The mechanisms of sterilization and decontamination of surfaces are compared in direct and post discharge plasma treatments in two low-pressure reactors, microwave and inductively coupled plasma. It is shown that the removal of various biomolecules, such as proteins, pyrogens or peptides, can be obtained at high rates and low temperatures in the inductively coupled plasma (ICP) by using Ar/O 2 mixtures. Similar efficiency is obtained for bacterial spores. Analysis of the discharge conditions illustrates the role of ion bombardment associated with O radicals, leading to a fast etching of organic matter. By contrast, the conditions obtained in the post discharge lead to much lower etching rates but also to a chemical modification of pyrogens, leading to their deactivation. The advantages of the two processes are discussed for the application to the practical case of decontamination of medical devices and reduction of hospital infections, illustrating the advantages and drawbacks of the two approaches.
The second half of the 20th century can be characterized and named as the 'plasma era', as the plasma gathered scientific interest because of its special physical behaviour. Thus, it was considered as the fourth material state and the plasma physics began to form consequently. In addition to this, many important applications of plasma were discovered and put to use. Especially, in last few decades, there has been an increased interest in the use of cold atmospheric plasma in biochemical applications. Until now, thermal plasma has been commonly used in many bio-medical and other applications; however, more recent efforts have shown that plasma can also be produced at lower temperature (close to the environment temperature) by using ambient air in an open space (in atmospheric pressure). However, two aspects remain neglected: firstly, low-temperature plasma production with a large area, and secondly, acquiring the necessary knowledge and understanding the relevant interaction mechanisms of plasma species with microorganisms. These aspects are currently being investigated at the 'Demokritos' Plasma Laboratory in Athens, Greece with radio frequency (27.12 MHz and it integer harmonics)-driven sub-atmospheric pressure plasma (100 Pa). The first aspect was achieved with atmospheric plasma being produced at a low temperature (close to the environment temperature) and in a large closed space systems. Regarding the plasma effect on living microorganisms, preliminary experiments and findings have already been carried out and many more have been planned for the near future.
Dielectric barrier discharge (DBD) devices are known ozone generators. Authors have previously demonstrated a DBD surface plasma source, operating in air at atmospheric pressure, to achieve killing of vegetative cells in 2-3 min and sterilization in 20 min (bacterial spores). The aim of this paper is to examine the role of the ozone in surface DBD plasma sterilization. The role of ozone in plasma killing is examined by a) characterizing the rate of production/decay of ozone during DBD plasma generation, b) studying the effect of exposing bacteria (Escherichia coli) solely to the ozone thus produced. Our results indicate that while ozone plays a major role, the energy flux delivered to the electrodes is also crucial in the process of plasma sterilization.