Analysis of sterilization effect by pulsed dielectric barrier discharge

Atmospheric pressure (AP) plasmas can sterilize against almost all kinds of bacteria because many ions and reactive species, such as oxygen atoms and ozone, etc., are generated during AP plasmas. So AP plasmas are proper processes for application to air cleaners and sterilizers. The aim of this paper is to evaluate a germicidal effect caused by pulsed plasma system in air utilizing a dielectric barrier discharge (DBD) type reactor incorporating alumina, glass, etc. Escherichia coli, Bacillus subtilis and Pseudomonas aeruginosa bacteria were used for this sterilization experiment. For analysis of the relationship between sterilization results and chemical species generated in the discharge, we used optical emission spectroscopy and we checked emission spectra by atomic oxygen (394.2 and 436.8 nm) and second positive system of nitrogen (337.1 nm). Experimental results showed that DBD treatment during 70 s sterilized E. coli with 99.99% effectively and ozone molecules were the dominant germicidal species. From these results we concluded that the pulsed DBD system is very effective for sterilization.     

Modeling the elimination of mature biofilms formed by Staphylococcus aureus and Salmonella spp. Using combined ultrasound and disinfectants

Biofilm formation by foodborne pathogens on food processing surfaces has contributed to numerous disease outbreaks and food recalls. We evaluated the following strategies for elimination of mature biofilm formed by Staphylococcus aureus and Salmonella spp. on stainless steel surfaces: acidic electrolyzed water (AEW), ozone water (OW), or ultrasound (40 kHz) alone, and combinations of ultrasound and disinfectants. The dynamics of elimination by combinations were determined using the Weibull and biphasic models. Treatment with AEW alone reduced the number of biofilm cells by approximately 3.0 log cfu/cm², whereas less than 0.8 log cfu/cm² of cells reduction was observed in biofilm exposed to OW or ultrasound alone, even with treatment for 20 min. The combination of AEW and ultrasound produced an obvious synergistic effect on biofilm reduction, achieving approximately 4.8 log cfu/cm² reduction in Salmonella spp. biofilm. Interestingly, the biphasic model was a better fit than the Weibull model for the elimination process of mature biofilm formed by both pathogens and subjected to a combination of ultrasound and AEW, as determined by smaller values of the statistical parameters RMSE and AIC, although both models could evaluate the dynamic processes. Our findings indicated that a combination of ultrasound and AEW could effectively reduce the biofilm formed by pathogens on food contact surfaces, and that the biphasic model could predict the number of residual cells after biofilm exposure to this intervention approach.     

Effect of dry-ozone exposure on different polymer surfaces and their resulting biocidal action on sporulated bacteria

The current work describes a novel technique by which certain types of polymers subjected to dry gaseous ozone acquire the ability to inactivate microorganisms, including those as resistant as bacterial spores. The originality and advantages of this ozone treatment of polymer surfaces rest on its simplicity (achieved at ambient temperature and pressure, a one step process …) and its efficacy. The inactivation efficiency is found to be specific to the nature of the treated polymer: 24 h after deposition of 10⁶ B. atrophaeus spores from a 100 µL suspension, high inactivation rates are observed with polymethyldisiloxane (99.997%, almost 5 log) and polystyrene (99.7%, more than 2 log), a lower rate with polyurethane (99.1%, 2 log) whereas polytetrafluoroethylene shows no detectable biocidal activity. Changes in hydrophilicity of these surfaces are monitored by means of contact-angle measurements while topographic modifications are characterized through atomic force microscopy. Ozone exposure brings about important topographic changes and chemical modifications on some polymers, which can be correlated with oxidation processes, increased wettability and surface energy. Variations of the dispersive and non-dispersive (polar) components of the surface energy are partially correlated with the polymer biocidal response. Furthermore, the basic component of the treated polymer (in contrast to its acidic component) seems to be correlated with the biocidal activity of the treated surfaces. Chemical species bearing ester groups, probably partially-oxidized styrene oligomers, as revealed by chemical analysis, could be involved in the biocidal activity. On practical grounds, since some of these treated polymers can strongly reduce microorganism loads on their surfaces, they could be particularly useful in hospital environment.     

Synergetic effects of ultrasound and slightly acidic electrolyzed water against Staphylococcus aureus evaluated by flow cytometry and electron microscopy

This study evaluated the synergetic effects of ultrasound and slightly acidic electrolyzed water (SAEW) on the inactivation of Staphylococcus aureus using flow cytometry and electron microscopy. The individual ultrasound treatment for 10 min only resulted in 0.36 log CFU/mL reductions of S. aureus, while the SAEW treatment alone for 10 min resulted in 3.06 log CFU/mL reductions. The log reductions caused by combined treatment were enhanced to 3.68 log CFU/mL, which were greater than the sum of individual treatments. This phenomenon was referred to as synergistic effects. FCM analysis distinguished live and dead cells as well as revealed dynamic changes in the physiological states of S. aureus after different treatments. The combined treatment greatly reduced the number of viable but nonculturable (VBNC) bacteria to 0.07%; in contrast, a single ultrasound treatment for 10 min induced the formation of VBNC cells to 45.75%. Scanning and transmission electron microscopy analysis revealed that greater damage to the appearance and ultrastructure of S. aureus were achieved after combined ultrasound-SAEW treatment compared to either treatment alone. These results indicated that combining ultrasound with SAEW is a promising sterilization technology with potential uses for environmental remediation and food preservation.     

等离子体放电活化生理盐水杀菌应用研究

等离子体中含有多种活性物种可实现高效安全杀菌,活性物种与生物体相互作用多在水环境下进行.因此等离子体与水的相互作用过程研究掀起了等离子体生物杀菌的新浪潮.本文采用水中阵列放电产生等离子体活化生理盐水,利用所产生的活化生理盐水对大肠杆菌开展了杀菌消毒研究,当等离子体放电时间达到120 s时产生的活化生理盐水与大肠杆菌混合后可使大肠杆菌的存活效率降至0.001%.通过紫外-可见吸收光谱测量及化学氧化还原沉降滴定表明放电电荷及激发态氧化性活性物种与水溶液相互作用,转化为活化生理盐水中长寿命相对稳定存在的H_2O_2和O_3等氧化性物种,与大肠杆菌作用并主导主要杀菌效果.     

Bacillus subtilis devitalization mechanism of atmosphere pressure plasma jet

Bio-applications of atmospheric pressure plasma have been widely studied in recent years. However, the devitalization mechanisms of micro-organisms by atmosphere pressure plasma have not been clearly explained. This paper was to find the possible sterilization mechanisms and define the major sterilization factors with the atmospheric pressure plasma jet. For the sterilization target, the Bacillus subtilis was selected. In this paper, a set of physical or chemical methods were used to characterize the following sterilization factors: heat, ultraviolet radiation, charged species and chemical reactive species generated by the plasma. It was found that the bacterial inactivation efficacy had a significant improvement when oxygen was introduced into the plasma jet system. Comparing with the result of sterilization, the inactivation process was dominantly controlled by synergistic actions of chemically active species and charged species, rather than heat, or ultraviolet radiation.     

The interaction of oxygen and ozone with pentacene

We use ultraviolet photoemission spectroscopy (UPS) to investigate the effect of oxygen and air exposure on pentacene thin film electronic structure. It is found that O₂ and water do not react noticeably with pentacene on the timescale of several hours, whereas a mixture of oxygen atoms, singlet oxygen and ozone readily oxidizes the organic compound. We obtain no evidence for irreversible intercalation of oxygen into pentacene or considerable p-type doping after re-evacuation. Infrared spectroscopy and atomic force microscopy are used to study the oxidation of pentacene thin films. Our data suggest the oxidation of pentacene with reactive oxygen species to yield highly volatile reaction products as evidenced by significant mass-losses of the films.     

Combination of ozone and ultrasonic-assisted aerosolization sanitizer as a sanitizing process to disinfect fresh-cut lettuce

Reduction of sanitizer dosage and development of non-immersion disinfection methods have become major focuses of research. Here, we examined the disinfection efficacy of combining gaseous ozone (4 and 8 ppm) with aerosolized oxidizing sanitizer [sodium hypochlorite (SH, 100 and 200 ppm)] and aerosolized organic acid [acetic acid (AA, 1% and 2%) and lactic acid (LA, 1% and 2%)]. Notably, 1% AA and 4 ppm gaseous ozone were ineffective for disinfecting Salmonella Typhimurium, and treatment with 1% AA + 8 ppm ozone caused browning of lettuce leaves and stimulated increases in aerobic mesophilic count (AMC), aerobic psychrotrophic count (APC), S. Typhimurium, and Escherichia coli O157:H7. Treatment with 2% LA + 8 ppm ozone resulted in the lowest S. Typhimurium, E. coli O157:H7, Listeria monocytogenes, AMC, APC, and molds and yeasts during storage (0–7 days at 4 °C). Quality analysis indicates that LA + 8 ppm ozone and SH + 8 ppm ozone did not negatively affect L*, a*, b*, polyphenolic content, weight loss, and sensory properties; however, the levels of two individual phenolic compounds (3,4-dihydroxybenzoic acid and vanillin), responsible for phenylpropanoid synthesis, were significantly increased after treatment with 2% LA + 8 ppm ozone. These findings provided insights into the use of LA combined with gaseous ozone for application in disinfecting fresh produce.     

Mechanism analysis of hydroxypropyl guar gum degradation in fracture flowback fluid by homogeneous sono-Fenton process

An effective hybrid system was applied as the first report for the successful treatment of key pollutants (hydroxypropyl guar gum, HPG) in fracturing flowback fluid, and the synergistic index of the hybrid system was 20.45. In this regard, chemical oxygen demand (COD) removal ratio was evaluated with various influencing operating factors including reaction time, H₂O₂ concentration, Fe²⁺ concentration, ultrasonic power, initial pH, and temperature. The optimal operating parameters by single-factor analysis method were: the pH of 3.0, the H₂O₂ concentration of 80 mM, the Fe²⁺ concentration of 5 mM, the ultrasonic power of 180 W, the ultrasonic frequency of 20–25 kHz, the temperature of 39 ℃, the reaction time of 30 min, and the COD removal rate reached 81.15 %, which was permissible to discharge surface water sources based on the environmental standards. A possible mechanism for HPG degradation and the generation of reactive species was proposed. Results of quenching tests showed that various impacts of the decomposition rate by addition of scavengers had followed the order of EDTA-2Na < BQ < t-BuOH, therefore OH radicals had a dominant role in destructing the HPG. Based on the kinetic study, it was concluded that Chan Kinetic Model was more appropriate to describe the degradation of HPG. Identification of intermediates by GC–MS showed that a wide range of recalcitrant compounds was removed and/or degraded into small molecular compounds effectively after treatment. Under the optimal conditions, the sono-Fenton system was used to treat the fracturing flowback fluid with the initial COD value of 675.21 mg/L, and the COD value decreased to 80.83 mg/L after 60 min treatment, which was in line with the marine sewage discharge standard. In conclusion, sono-Fenton system can be introduced as a successful advanced treatment process for the efficient remediation of fracture flowback fluid.     

The responses of Ht22 cells to oxidative stress induced by buthionine sulfoximine (BSO)

Background  

glutathione (GSH) is the most abundant thiol antioxidant in mammalian cells. It directly reacts with reactive oxygen species (ROS), functions as a cofactor of antioxidant enzymes, and maintains thiol redox potential in cells. GSH depletion has been implicated in the pathogenesis of neurological diseases, particularly to Parkinson's disease (PD). The purpose of this study was to investigate the change of cellular antioxidant status and basic cell functions in the relatively early stages of GSH depletion.     

Incomplete ozone recovery effect in the presence of active oxygen species

The degree of ozone recovery after pulsed UV laser photolysis of O₂-O₃-Ar mixture is measured using time-resolved absorption spectroscopy. The effect of incomplete ozone recovery in the presence of molecular singlet oxygen O₂(a ¹Δ) and atomic oxygen is detected. This effect is caused by the reaction between the vibrationally excited ozone molecule formed due to recombination and atomic oxygen. The branching factor for the chemical channel of reaction products is γ _r = 0.81 ± 0.13.     

Quantitative analysis of oxidative DNA damage induced by high-voltage pulsed discharge with cavitation

Pulsed discharge is used for sterilization and disinfection, but the details of the molecular mechanisms remain largely unknown. Since pulsed discharge generates reactive oxygen species (ROS), we analyzed the oxidative DNA damages after pulsed discharge treatment to consider the involvement of ROS in the damaging process. We applied pulsed discharge with cavitation to plasmid DNA molecules and estimated the yields of the damages by agarose gel electrophoresis. The treated DNA contained various oxidative DNA damages, including single and double strand breaks and base lesions. The yields of the damages increased in response to the energy used for pulsed discharge. We also measured the yield of 8-hydroxyguanine (8-OH-G), one of the major oxidative base lesions, in the treated plasmid DNA by mass spectrometry quantitatively and found that the yield of the oxidative base lesion corresponded to the increment of the applied energy. In addition, we observed the involvement of mutM gene, which is responsible for repair of 8-OH-G, in the increased sensitivity of Escherichia coli to pulsed discharge. Therefore, ROS seem to mediate the sterilization ability of pulsed discharge.     

Escherichia coli deactivation study controlling the atmospheric pressure plasma discharge conditions

Bio-applications of plasma have been widely studied in recent years. However, considering the high interests, the inactivation mechanisms of micro-organisms by plasma have not been clearly explained. The goal of this study was to find the sterilization mechanisms and define the major sterilization factors with the atmospheric pressure radio-frequency helium glow discharge. For the sterilization target the Escherichia coli was used. To begin with the sterilization study, the plasma characteristics were investigated by means of electrical and optical diagnostics. Especially, the gas temperature was controlled under 50 °C by keeping the input power less than 70 W to eliminate the thermal effects. Contribution of the UV irradiation from the plasma was studied and it turned out to be negligible. On the other hand, it was found that the sterilization was more effective up to 40% with only 0.15% oxygen addition to the helium supply gas. It indicates that the inactivation process was dominantly controlled by oxygen radicals, rather than heat or UV photons.     

Synergistic bactericidal effect of ultrasound combined with citral nanoemulsion on Salmonella and its application in the preservation of purple kale

In this study, a novel citral nanoemulsion (CLNE) was prepared by ultrasonic emulsification. The synergistic antibacterial mechanism of ultrasound combined with CLNE against Salmonella Typhimurium and the effect on the physicochemical properties of purple kale were investigated. The results showed that the combined treatment showed obviously inactivate effect of S. Typhimurium. Treatment with 0.3 mg/mL CLNE combined with US (20 kHz, 253 W/cm²) for 8 min reduced S. Typhimurium populations in phosphate-buffered saline (PBS) by 9.05 log CFU/mL. Confocal laser scanning microscopy (CLSM), flow cytometry (FCM), protein and nucleic acid release assays showed that the US combination CLNE disrupt the integrity of S. Typhimurium membranes. Reactive oxygen species (ROS) and malondialdehyde (MDA) detection indicated that US+CLNE exacerbated oxidative stress and lipid peroxidation in cell membranes. The morphological changes of cells after different treatments by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) illustrated that the synergistic effect of US+CLNE treatment changed the morphology and internal microstructure of the bacteriophage cells. Application of US+CLNE on purple kale leaves for 6 min significantly (P < 0.05) reduced the number of S. Typhimurium, but no changes in the physicochemical properties of the leaves were detected. This study elucidates the synergistic antibacterial mechanism of ultrasound combined with CLNE and provides a theoretical basis for its application in food sterilization.     

Mechanism and dynamic study of reactive red X-3B dye degradation by ultrasonic-assisted ozone oxidation process

The effectiveness of ozone combined with ultrasound techniques in degrading reactive red X-3B is evaluated. A comparison among ozone (O₃), ultrasonic (US), ozone/ultrasonic (O₃/US) for degradation of reactive red X-3B has been performed. Results show that O₃/US system was the most effective and the optimally synergetic factor reaches to 1.42 in O₃/US system. The cavitation of ultrasound plays an important role during the degradation process. It is found that 99.2% of dye is degraded within 6 min of reaction at the initial concentration of 100 mg·L⁻¹, pH of 6.52, ozone flux of 40 L·h⁻¹ and ultrasonic intensity of 200 W·L⁻¹. Ozonation reactions in conjunction with sonolysis indicate that the decomposition followed pseudo-first-order reaction kinetics but the degradation efficiencies are affected by operating conditions, particularly initial pH and ultrasonic intensity. A kinetic model is established based on the reaction corresponding to operational parameters. In addition, the main reaction intermediates, such as p-benzoquinone, catechol, hydroquinone, phthalic anhydride and phthalic acid, are separated and identified using GC/MS and a possible degradation pathway is proposed during the O₃/US process.     

Plasma sterilization using the RF glow discharge

In the present work, glow discharge oxygen plasma was used to sterilize the Pseudomonas aeruginosa on the polyethylene terephthalate (PET) sheets. In a self-designed plasma reaction equipment, active species (electron, ion, radical, UV light, etc.) were separated effectively, and the discharge area, afterglow area and remote area were plotted out in the plasma field. Before and after plasma treatment the cell morphology was studied by scanning electron microscopy (SEM). The results showed that after treatment of 30 s the germicidal effect is 4.26, 3. 84, 2.61, respectively in the three areas on the following conditions: discharge power was 40 W and gas flux was 20 cm³/min. SEM results revealed the cell morphology before and after plasma treatment. The walls or cell membrane cracking was testified by determining the content of protein using coomassie light blue technique. The results from electron spin resonance spectroscopy (ESR) and double Langmuir electron probe showed that electron, ion and oxygen free radical played important roles in sterilization in the discharge area, but only oxygen radicals acted to sterilize the bacteria in the afterglow area and the remote area.     

An overview of research using the one atmosphere uniform glowdischarge 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 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     

Ultrasound-assisted blue light killing Vibrio parahaemolyticus to improve salmon preservation

Vibrio parahaemolyticus is a typical marine bacterium, which often contaminates seafood and poses a health risk to consumers. Some non-thermal sterilization technologies, such as ultrasonic field (UF) and blue light (BL) irradiation, have been widely used in clinical practice due to their efficiency, safety, and avoidance of drug resistance, but their application in food preservation has not been extensively studied. This study aims to investigate the effect of BL on V. parahaemolyticus in culture media and in ready-to-eat fresh salmon, and to evaluate the killing effectiveness of the UF combined with BL treatment on V. parahaemolyticus. The results showed that BL irradiation at 216 J/cm² was effective in causing cell death (close to 100%), cell shrinkage and reactive oxygen species (ROS) burst in V. parahaemolyticus. Application of imidazole (IMZ), an inhibitor of ROS generation, attenuated the cell death induced by BL, indicating that ROS were involved in the bactericidal effects of BL on V. parahaemolyticus. Furthermore, UF for 15 min enhanced the bactericidal effect of BL at 216 J/cm² on V. parahaemolyticus, with the bactericidal rate of 98.81%. In addition, BL sterilization did not affect the color and quality of salmon, and the additive UF treatment for 15 min did not significant impact on the color of salmon. These results suggest that BL or UF combined with BL treatment has potential for salmon preservation, however, it is crucial to strictly control the intensity of BL and the duration of UF treatment to prevent reducing the freshness and brightness of salmon.     

Nb doping effect on TiO2−x films for bolometer applications

Nb-doped TiO_2−x thin films were deposited using a 1 at% niobium doped titanium target by RF reactive magnetron sputtering at various oxygen partial pressures (pO₂). The films appeared amorphous in the pO₂ range of 4.4–4.7% with resistivity ranging from 0.39 Ω cm to 2.48 Ω cm. Compared to pure TiO_2−x films, the resistivity of the Nb-doped TiO_2−x films did not change sensitively with the oxygen partial pressure, indicating that the resistivity of the films can be accurately controlled. 1/f noise parameter of Nb-doped TiO_2−x films were found to decrease largely while the measured temperature coefficient of resistance (TCR) of the films was still high. The obtained results indicate that Nb-doped TiO_2−x films have great potential as an alternative bolometric material.