Advances in atmospheric pressure plasma-based optical emission spectrometry for the analysis of heavy metals

Over the past decade, miniaturized optical emission spectrometry (OES) systems utilizing atmospheric pressure plasmas (APPs) as radiation sources have exhibited impressive capabilities in trace heavy metal analysis. As the core of the analytical system, APPs sources possess unique properties such as compact size, light weight, low energy requirement, ease of fabrication, and relatively low manufacturing cost. This critical review focuses on recent progress of APP-based OES systems employed for the determination of heavy metals. Influences of technical details including the sample introduction manner, the sampling volume, the sample flow rate, the pH of the solutions on the plasma stability and the intensity of analytical signals are comprehensively discussed. Furthermore, the review emphasizes the analytical challenges faced by these techniques and highlights the opportunities for further development in the field of heavy metal detection.

Inactivation of Escherichia coli in apple cider using atmospheric cold plasma

Atmospheric cold plasma (ACP) is a promising non-thermal technology that has the potential to inactivate microorganisms in foods. In this work, the inactivation of E. coli K12, acid-adapted E. coli K12, and E. coli O157:H7 in apple cider by ACP was investigated using feed gases as simulated air (SA) (80 % N₂ + 20 % O₂) and a mixture of 90 % N₂ + 10 % O₂ with various processing times (0 to 180 s). We obtained the reduced the populations of both acid-adapted and non-adapted E. coli K12 by 5 log CFU/mL within 120 s, and E. coli O157:H7 within 90 s. Additionally, no significant changes in the °Brix, pH, temperature, or titratable acidity (TA) of apple cider were observed after exposure to ACP. However, processing times longer than 120 s resulted in significant changes in the pH values. The highest concentration of ozone and hydrogen peroxide reached to 0.22 ± 0.1 mg/L for CG in 180 s and 0.07 ± 0.01 mg/L for SA in 150 s, respectively. Both acid-adapted and non-acid adapted E. coli K12 was found to be more resistant to ACP processing than E. coli O157:H7 after the 90 s, so it could serve as a surrogate for E. coli O157:H7. When we compared the effect of the gas type on inactivation, non-selective media, the results showed no significant differences between the gas types, while selective media demonstrated significant differences. In optical absorption spectroscopy measurements of plasma species, primarily ozone peaks were observed. Furthermore, the optical absorption spectroscopy also revealed that the inactivation of the bacteria could be attributed to some plasma species with wavelengths between 190 and 308 nm. The findings provided a perspective on the use of ACP as a method for decontaminating fruit juices as a non-thermal processing.

UV/ozone surface modification combined with atmospheric pressure plasma irradiation for cell culture plastics to improve pluripotent stem cell culture

Culturing pluripotent stem cells effectively requires substrates coated with feeder cell layers or cell-adhesive matrices. It is difficult to employ pluripotent stem cells as resources for regenerative medicine due to risks of culture system contamination by animal-derived factors, or the large costs associated with the use of adhesive matrices. To enable a coating-free culture system, we focused on UV/ozone surface modification and atmospheric pressure plasma treatment for polystyrene substrates, to improve adhesion and proliferation of pluripotent stem cells. In this study, to develop a feeder- and matrix coating-free culture system for embryonic stem cells (ESCs), mouse ESCs were cultured on polystyrene substrates that were surface-modified using UV/ozone-plasma combined treatment. mESCs could be successfully cultured under feeder-free conditions upon UV/ozone-plasma combined treatment of culture substrates, without any further chemical treatments, and showed similar proliferation rates to those of cells grown on the feeder cell layer or matrix-coated substrates.

Synthesis of antibacterial composite coating containing nanocapsules in an atmospheric pressure plasma

Antibacterial coating is an important strategy preventing bacterial colonization and biofilm formation. One-step synthesis of nanocapsule-containing antibacterial coatings with controlled release of Ag⁺ ions was achieved in the current work by aerosol-assisted atmospheric pressure plasma deposition. The experimental parameters of deposition including the discharge power, silver nitrate concentration, aerosol flow rate, continuous and pulsed mode of operation were studied in order to analyze their effects on surface morphology and chemical composition of the coating. Formation of nanocapsules embedded in the polymeric coating was observed. A core-shell structure was found for nanocapsule with silver in the core and polymer in the shell. Antibacterial coatings on polyethylene terephthalate film were studied in terms of Ag⁺ ion release, antibacterial properties against Escherichia coli and Staphylococcus aureus, and cytotoxicity with murine fibroblasts. Two-phase release kinetics of Ag⁺ ions was observed as initially a short-term burst release followed by a long-term slow release. It was revealed that high antibacterial efficiency of the coatings deposited on polyethylene terephthalate films can be coupled with low cytotoxicity. These biocompatible antibacterial coatings are very promising in different fields including biological applications.

Oxygen radical based on non-thermal atmospheric pressure plasma alleviates lignin-derived phenolic toxicity in yeast

BACKGROUND

Vanillin is the main byproduct of alkaline-pretreated lignocellulosic biomass during the process of fermentable-sugar production and a potent inhibitor of ethanol production by yeast. Yeast cells are usually exposed to vanillin during the industrial production of bioethanol from lignocellulosic biomass. Therefore, vanillin toxicity represents a major barrier to reducing the cost of bioethanol production.

RESULTS

In this study, we analysed the effects of oxygen-radical treatment on vanillin molecules. Our results showed that vanillin was converted to vanillic acid, protocatechuic aldehyde, protocatechuic acid, methoxyhydroquinone, 3,4-dihydroxy-5-methoxybenzaldehyde, trihydroxy-5-methoxybenzene, and their respective ring-cleaved products, which displayed decreased toxicity relative to vanillin and resulted in reduced vanillin-specific toxicity to yeast during ethanol fermentation. Additionally, after a 16-h incubation, the ethanol concentration in oxygen-radical-treated vanillin solution was 7.0-fold greater than that from non-treated solution, with similar results observed using alkaline-pretreated rice straw slurry with oxygen-radical treatment.

CONCLUSIONS

This study analysed the effects of oxygen-radical treatment on vanillin molecules in the alkaline-pretreated rice straw slurry, thereby finding that this treatment converted vanillin to its derivatives, resulting in reduced vanillin toxicity to yeast during ethanol fermentation. These findings suggest that a combination of chemical and oxygen-radical treatment improved ethanol production using yeast cells, and that oxygen-radical treatment of plant biomass offers great promise for further improvements in bioethanol-production processes.

Measurement of OH radicals distribution in a microwave plasma sheet using LIF method

Microwave plasma sources (MPSs) operating at atmospheric pressure provide plasmas in the form of a flame or cylindrical column. In contrast, this article presents an innovative MPS (patented by us) for generating a new type of plasma, i.e. in the form of a plasma sheet, which is generated in a flat cuboidal quartz box. It is based on a WR 340 waveguide, powered by microwaves of 2.45 GHz and operated in argon at atmospheric pressure. The plasma sheet contains a multitude of filaments typical of microwave argon plasmas. In the presented experiment, the spatial distribution of the OH radicals in the microwave plasma sheet was measured by means of the LIF method. Studies have shown that the relative concentration of OH radicals increases with the increase in microwave power and decreases with the increasing argon flow rate.

Anti-diabetic effects of trans-resveratrol byproducts induced by plasma treatment

Cold plasma processing has emerged a promising green technology with great potential to improve the quality and microbial safety of various minimally processed foods and materials. However, studies on non-thermal plasma-induced chemical interactions between major food ingredients that might change chemical structure and biological properties are very sparse. Thus, the objective of this study was to evaluate the influence of a dielectric barrier discharge (DBD) treatment on principal trans-resveratrol (TR) in several food stuffs by spectroscopic (HPLC, NMR, MS) and biological analyses. TR was dissolved in methanol and directly exposed to atmospheric non-thermal plasma field at 250 W for different durations (10, 20, 40, and 60 min), 40% relative humidity, and 25 °C. TR treated with plasma for 40 min showed greatly enhanced inhibitory activities for α-glucosidase and α-amylase than parent TR. Newly generated unusual compounds (1, 2) and known compounds (3-6) from plasma treated TR for 40 min were characterized using chromatographic and spectroscopic methods. The predominant reaction of TR induced by cold plasma followed by typical dimerization of products included methylene bridge formation and cyclization of TR. Among predominantly generated products, new compounds 1 and 2 showed more potent α-glucosidase and α-amylase inhibition capacities than parent TR. These results might be used to modify structures and enhance biological property of TR during food processing using DBD plasma treatment.

Determination of proper treatment time for in vivo blood coagulation and wound healing application by non-thermal helium plasma jet

The aim of this research was to determine the time of blood coagulation of in vivo cuts that treated by the non-thermal atmospheric pressure plasma jet. Also, the effect of different treatment times on wound healing has been studied. The non-thermal atmospheric pressure plasma jet working in helium gas has been used. The averaged treatment time of 8.6 s for in vivo cuts on the Balb/c mouse liver showed the complete blood coagulation. Also, the effect of tretament time on wound healing has been studied by applying plasma on the wounds for different times (10, 20, 30, 40 and 50 s). It was obtained from morphological analysis that the treatment groups of 30 s, 40 s and 50 s cause the wounds to be healed faster than the groups 10 s and 20 s.The histological analysis showed that in 30 s and 40 s treatment time groups, the repair process of treated wounds has been accelerated, while for 50 s group, it has not been completed, yet. The 30 s treatment time has been chosen because of imposing lower dose to living tissue. The treated wound area reduction ratios against the control wound reduction ratios for 30 s group were obtained 78%, 77% and 63% at the 3rd, 5th and 8th days, respectively.

Long-lived and short-lived reactive species produced by a cold atmospheric pressure plasma jet for the inactivation of Pseudomonas aeruginosa and Staphylococcus aureus

Different chemical pathways leading to the inactivation of Pseudomonas aeruginosa and Staphylococcus aureus by a cold atmospheric pressure plasma jet (APPJ) in buffered and non-buffered solutions are reported. As APPJs produce a complex mixture of reactive species in solution, a comprehensive set of diagnostics were used to assess the liquid phase chemistry. This includes absorption and electron paramagnetic resonance spectroscopy in addition to a scavenger study to assess the relative importance of the various plasma produced species involved in the inactivation of bacteria. Different modes of inactivation of bacteria were found for the same plasma source depending on the solution and the plasma feed gas. The inactivation of bacteria in saline is due to the production of short-lived species in the case of argon plasma when the plasma touches the liquid. Long-lived species (ClO^-) formed by the abundant amount of O^. radicals produced by the plasmas played a dominant role in the case of Ar + 1% O₂ and Ar + 1% air plasmas when the plasma is not in direct contact with the liquid. Inactivation of bacteria in distilled water was found to be due to the generation of short-lived species: O^. &O₂^.- for Ar + 1% O₂ plasma and O₂^.- (and ^.OH in absence of saline) for Ar plasma.

Assessment of microbial safety and quality changes of brown and white cooked rice treated with atmospheric pressure plasma

The microbial and physicochemical properties of brown and white cooked rice treated by atmospheric pressure plasma (APP). APP was produced (250 W, 15 kHz, ambient air) and applied to brown and white cooked rice for 5, 10, and 20 min. The 20-min plasma treatment reduced in bacterial counts by 2.01 log CFU/g when cooked rice were inoculated with Bacillus cereus or Escherichia coli O157:H7. The pH of the brown cooked rice was decreased by the 5-min plasma. The hardness values of APP-treated brown and white cooked rice were lower than untreated samples. The reducing sugar contents of brown and white cooked rice were significantly higher than those in untreated samples. Lipid oxidation of APP-treated brown and white cooked rice were higher compared to untreated samples. These results indicate that APP improves microbial quality, although further studies should be conducted to change the physicochemical qualities of brown and white cooked rice induced by APP.

Hydrophobic and superhydrophobic surfaces fabricated using atmospheric pressure cold plasma technology: A review

Hydrophobic surfaces are often used to reduce wetting of surfaces by water. In particular, superhydrophobic surfaces are highly desired for several applications due to their exceptional properties such as self-cleaning, anti-icing, anti-friction and others. Such surfaces can be prepared via numerous methods including plasma technology, a dry technique with low environmental impact. Atmospheric pressure plasma (APP) has recently attracted significant attention as lower-cost alternative to low-pressure plasmas, and as a candidate for continuous rather than batch processing. Although there are many reviews on water-repellent surfaces, and a few reviews on APP technology, there are hardly any review works on APP processing for hydrophobic and superhydrohobic surface fabrication, a topic of high importance in nanotechnology and interface science. Herein, we critically review the advances on hydrophobic and superhydrophobic surface fabrication using APP technology, trying also to give some perspectives in the field. After a short introduction to superhydrophobicity of nanostructured surfaces and to APPs we focus this review on three different aspects: (1) The atmospheric plasma reactor technology used for fabrication of (super)hydrophobic surfaces. (2) The APP process for hydrophobic surface preparation. The hydrophobic surface preparation processes are categorized methodologically as: a) activation, b) grafting, c) polymerization, d) roughening and hydrophobization. Each category includes subcategories related to different precursors used. (3) One of the most important sections of this review concerns superhydrophobic surfaces fabricated using APP. These are methodologically characterized as follows: a) single step processes where micro-nano textured topography and low surface energy coating are created at the same time, or b) multiple step processes, where these steps occur sequentially in or out of the plasma. We end the review with some perspectives in the field. We aspire to address scientists, who will get involved in the fields of (super)hydrophobicity and/or in atmospheric pressure plasma processing.

Oxygen-radical pretreatment promotes cellulose degradation by cellulolytic enzymes

BACKGROUND

The efficiency of cellulolytic enzymes is important in industrial biorefinery processes, including biofuel production. Chemical methods, such as alkali pretreatment, have been extensively studied and demonstrated as effective for breaking recalcitrant lignocellulose structures. However, these methods have a detrimental effect on the environment. In addition, utilization of these chemicals requires alkali- or acid-resistant equipment and a neutralization step.

RESULTS

Here, a radical generator based on non-thermal atmospheric pressure plasma technology was developed and tested to determine whether oxygen-radical pretreatment enhances cellulolytic activity. Our results showed that the viscosity of carboxymethyl cellulose (CMC) solutions was reduced in a time-dependent manner by oxygen-radical pretreatment using the radical generator. Compared with non-pretreated CMC, oxygen-radical pretreatment of CMC significantly increased the production of reducing sugars in culture supernatant containing various cellulases from Phanerochaete chrysosporium. The production of reducing sugar from oxygen-radical-pretreated CMC by commercially available cellobiohydrolases I and II was 1.7- and 1.6-fold higher, respectively, than those from non-pretreated and oxygen-gas-pretreated CMC. Moreover, the amount of reducing sugar from oxygen-radical-pretreated wheat straw was 1.8-fold larger than those from non-pretreated and oxygen-gas-pretreated wheat straw.

CONCLUSIONS

Oxygen-radical pretreatment of CMC and wheat straw enhanced the degradation of cellulose by reducing- and non-reducing-end cellulases in the supernatant of a culture of the white-rot fungus P. chrysosporium. These findings indicated that oxygen-radical pretreatment of plant biomass offers great promise for improvements in lignocellulose-deconstruction processes.

Investigation of blood coagulation effect of nonthermal multigas plasma jet in vitro and in vivo

BACKGROUND

Nonthermal atmospheric pressure plasma (NTAPP) has recently received attention as a novel tool in medicine. It is thought that plasma components yield plasma effects such as sterilization, blood coagulation, and wound healing. These effects are produced without thermal damage. We investigated the blood coagulation effect of NTAPP by using a multigas plasma jet.

MATERIALS AND METHODS

Multigas plasma jets can generate NTAPP by several gas species. In this study, argon, oxygen, helium, nitrogen, mock air, and carbon dioxide were used to generate NTAPP, and blood coagulation times were compared with each plasma-treated sample. The NTAPP blood coagulation effects on whole blood with four different anticoagulants were investigated. In addition, in this study, the effects of plasma treatment on porcine tissues and organs were investigated as in vivo experiment.

RESULTS

A tendency to coagulate later with argon gas plasma than others was shown. There were no significant differences between oxygen, helium, nitrogen, mock air, and carbon dioxide. Whole blood with each anticoagulant demonstrated fast coagulation by NTAPP treatment. Fast control of the bleeding lesions on porcine stomach and liver by plasma treatment was observed, and no tissue damage due to the plasma treatment was detected by optical microscope.

CONCLUSIONS

These experiments suggest the potential of various gas NTAPPs as a novel medical device to control bleeding lesions.

Plasma inactivation of microorganisms on sprout seeds in a dielectric barrier discharge

Fresh produce is frequently contaminated by microorganisms, which may lead to spoilage or even pose a threat to human health. In particular sprouts are considered to be among the most risky foods sold at retail since they are grown in an environment practically ideal for growth of bacteria and usually consumed raw. Because heat treatment has a detrimental effect on the germination abilities of sprout seeds, alternative treatment technologies need to be developed for microbial inactivation purposes. In this study, non-thermal plasma decontamination of sprout seeds is evaluated as a promising option to enhance food safety while maintaining the seed germination capabilities. In detail, investigations focus on understanding the efficiency of non-thermal plasma inactivation of microorganisms as influenced by the type of microbial contamination, substrate surface properties and moisture content, as well as variations in the power input to the plasma device. To evaluate the impact of these parameters, we studied the reduction of native microbiota or artificially applied E. coli on alfalfa, onion, radish and cress seeds exposed to non-thermal plasma in an atmospheric pressure pulsed dielectric barrier discharge streamed with argon. Plasma treatment resulted in a maximum reduction of 3.4 logarithmic units for E. coli on cress seeds. A major challenge in plasma decontamination of granular food products turned out to be the complex surface topology, where the rough surface with cracks and crevices can shield microorganisms from plasma-generated reactive species, thus reducing the treatment efficiency. However, improvement of the inactivation efficiency was possible by optimizing substrate characteristics such as the moisture level and by tuning the power supply settings (voltage, frequency) to increase the production of reactive species. While the germination ability of alfalfa seeds was considerably decreased by harsh plasma treatment, enhanced germination was observed under mild conditions. In conclusion, the results from this study indicate that cold plasma treatment represents a promising technology for inactivation of bacteria on seeds used for sprout production while preserving their germination properties.

In situ coupling of chitosan onto polypropylene foils by an Atmospheric Pressure Air Glow Discharge with a liquid cathode

Atmospheric air plasma treatment of chitosan solutions leads to degradation of chitosan molecules by OH radicals and is accompanied by a predominant cleavage of glycosidic linkages and by a decrease of the molecular weight. The degradation proceeds via first order kinetics with the rate constant of (5.73±0.22)×10(-6)s(-1) and the energetic yield of chitosan bond scission of (2.4±0.2)×10(-8)mol/J. Products of degradation together with intact chitosan molecules adsorb and form coatings on polypropylene foils immersed into the solution that is being plasma treated. The plasma treatment results in strong binding of chitosan to polypropylene due to the formation of covalent bonds between the activated polymer surface and chitosan molecules. Plasma-driven crosslinking is responsible for the accumulation of compressive stress which leads to the development of buckling instabilities in the chitosan coatings.

Nanopore formation process in artificial cell membrane induced by plasma-generated reactive oxygen species

We investigated morphological change of an artificial lipid bilayer membrane induced by oxygen radicals which were generated by non-equilibrium atmospheric pressure plasma. Neutral oxygen species, O((3)Pj) and O2((1)Δg), were irradiated of a supported lipid bilayer existing under a buffer solution at various conditions of dose time and distances, at which the dose amounts of the oxygen species were calculated quantitatively. Observation using an atomic force microscope and a fluorescence microscope revealed that dose of the neutral oxygen species generated nanopores with the diameter of 10-50 nm in a phospholipid bilayer, and finally destructed the bilayer structure. We found that protrusions appeared on the lipid bilayer surface prior to the formation of nanopores, and we attributed the protrusions to the precursor of the nanopores. We propose a mechanism of the pore formation induced by lipid oxidation on the basis of previous experimental and theoretical studies.

Decontamination of Aspergillus flavus and Aspergillus parasiticus spores on hazelnuts via atmospheric pressure fluidized bed plasma reactor

In this study, an atmospheric pressure fluidized bed plasma (APFBP) system was designed and its decontamination effect on aflatoxigenic fungi (Aspergillus flavus and Aspergillus parasiticus) on the surface of hazelnuts was investigated. Hazelnuts were artificially contaminated with A. flavus and A. parasiticus and then were treated with dry air plasma for up to 5min in the APFBP system at various plasma parameters. Significant reductions of 4.50 log (cfu/g) in A. flavus and 4.19 log (cfu/g) in A. parasiticus were achieved after 5min treatments at 100% V - 25kHz (655W) by using dry air as the plasma forming gas. The decontamination effect of APFBP on A. flavus and A. parasiticus spores inoculated on hazelnuts was increased with the applied reference voltage and the frequency. No change or slight reductions were observed in A. flavus and A. parasiticus load during the storage of plasma treated hazelnuts whereas on the control samples fungi continued to grow under storage conditions (30days at 25°C). Temperature change on hazelnut surfaces in the range between 35 and 90°C was monitored with a thermal camera, and it was demonstrated that the temperature increase taking place during plasma treatment did not have a lethal effect on A. flavus and A. parasiticus spores. The damage caused by APFBP treatment on Aspergillus spp. spores was also observed by scanning electron microscopy.

Effect of atmospheric pressure plasma jet on the foodborne pathogens attached to commercial food containers

Bacterial biofilms are associated with numerous infections and problems in the health care and food industries. The aim of this study was to evaluate the bactericidal effect of an atmospheric pressure plasma (APP) jet on Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Typhimurium biofilm formation on collagen casing (CC), polypropylene (PP) and polyethylene terephthalate (PET), which are widely used food container materials. The samples were treated separately with the APP jet at a 50-W input power for 5 and 10 min, and nitrogen (6 l per minute) gas combined with oxygen (10 standard cubic centimeters per minute) was used to produce the APP. The APP jet reduced the number of bacterial cells in a time-dependent manner. All pathogens attached to CC, PP, and PET were reduced by 3-4 log CFU/cm(2) by the 10-min APP treatment. The developed APP jet was effectively reduced biofilms on CC, PP, and PET.

Bactericidal efficacy of atmospheric pressure non-thermal plasma (APNTP) against the ESKAPE pathogens

The emergence of multidrug-resistant pathogens within the clinical environment is presenting a mounting problem in hospitals worldwide. The 'ESKAPE' pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) have been highlighted as a group of causative organisms in a majority of nosocomial infections, presenting a serious health risk due to widespread antimicrobial resistance. The stagnating pipeline of new antibiotics requires alternative approaches to the control and treatment of nosocomial infections. Atmospheric pressure non-thermal plasma (APNTP) is attracting growing interest as an alternative infection control approach within the clinical setting. This study presents a comprehensive bactericidal assessment of an in-house-designed APNTP jet both against biofilms and planktonic bacteria of the ESKAPE pathogens. Standard plate counts and the XTT metabolic assay were used to evaluate the antibacterial effect of APNTP, with both methods demonstrating comparable eradication times. APNTP exhibited rapid antimicrobial activity against all of the ESKAPE pathogens in the planktonic mode of growth and provided efficient and complete eradication of ESKAPE pathogens in the biofilm mode of growth within 360s, with the exception of A. baumannii where a >4log reduction in biofilm viability was observed. This demonstrates its effectiveness as a bactericidal treatment against these pathogens and further highlights its potential application in the clinical environment for the control of highly antimicrobial-resistant pathogens.

Evaluation of bone response to synthetic bone grafting material treated with argon-based atmospheric pressure plasma

Bone graft materials are utilized to stimulate healing of bone defects or enhance osseointegration of implants. In order to augment these capabilities, various surface modification techniques, including atmospheric pressure plasma (APP) surface treatment, have been developed. This in vivo study sought to assess the effect of APP surface treatment on degradation and osseointegration of Synthograft™, a beta-tricalcium phosphate (β-TCP) synthetic bone graft. The experimental (APP-treated) grafts were subjected to APP treatment with argon for a period of 60s. Physicochemical characterization was performed by environmental scanning electron microscopy, surface energy (SE), and x-ray photoelectron spectroscopy analyses both before and after APP treatment. Two APP-treated and two untreated grafts were surgically implanted into four critical-size calvarial defects in each of ten New Zealand white rabbits. The defect samples were explanted after four weeks, underwent histological analysis, and the percentages of bone, soft tissue, and remaining graft material were quantified by image thresholding. Material characterization showed no differences in particle surface morphology and that the APP-treated group presented significantly higher SE along with higher amounts of the base material chemical elements on it surface. Review of defect composition showed that APP treatment did not increase bone formation or reduce the amount of soft tissue filling the defect when compared to untreated material. Histologic cross-sections demonstrated osteoblastic cell lines, osteoid deposition, and neovascularization in both groups. Ultimately, argon-based APP treatment did not enhance the osseointegration or degradation of the β-TCP graft. Future investigations should evaluate the utility of gases other than argon to enhance osseointegration through APP treatment.

Effect of atmospheric pressure dielectric barrier discharge plasma on the biological activity of naringin

The biological activity of naringin treated with atmospheric pressure plasma was evaluated to investigate whether exposure to plasma can be used as a method to improve the biological activity of natural materials. Naringin was dissolved in methanol (at 500 ppm) and transferred to a container. A dielectric barrier discharge (DBD) (250 W, 15 kHz, ambient air) was then generated. Treatment with the plasma for 20 min increased the radical-scavenging activity, FRAP value, and the total phenolic compound content of naringin from 1.45% to 38.20%, from 27.78 to 207.78 μM/g, and from 172.50 to 225.83 ppm, respectively. Moreover, the tyrosinase-inhibition effect of naringin increased from 6.12% to 83.30% upon plasma treatment. Naringin treated with plasma exhibited antimicrobial activity against foodborne pathogens, especially Salmonella Typhimurium; an activity that was absent before plasma treatment. Structural modifications induced in the naringin molecule by plasma might be responsible for improving the biological activity of naringin.

Atmospheric pressure plasmas: infection control and bacterial responses

Cold atmospheric pressure plasma (APP) is a recent, cutting-edge antimicrobial treatment. It has the potential to be used as an alternative to traditional treatments such as antibiotics and as a promoter of wound healing, making it a promising tool in a range of biomedical applications with particular importance for combating infections. A number of studies show very promising results for APP-mediated killing of bacteria, including removal of biofilms of pathogenic bacteria such as Pseudomonas aeruginosa. However, the mode of action of APP and the resulting bacterial response are not fully understood. Use of a variety of different plasma-generating devices, different types of plasma gases and different treatment modes makes it challenging to show reproducibility and transferability of results. This review considers some important studies in which APP was used as an antibacterial agent, and specifically those that elucidate its mode of action, with the aim of identifying common bacterial responses to APP exposure. The review has a particular emphasis on mechanisms of interactions of bacterial biofilms with APP.

Impact of cold plasma on Citrobacter freundii in apple juice: inactivation kinetics and mechanisms

Various studies have shown that cold plasma is capable of inactivating microorganisms located on a variety of food surfaces, food packaging materials and process equipment under atmospheric pressure conditions; however, less attention has been paid to the impact of cold plasma on microorganisms in liquid foodstuffs. The present study investigates cold plasma's ability to inactivate Citrobacter freundii in apple juice. Optical emission spectroscopy (OES) and temperature measurements were performed to characterise the plasma source. The plasma-related impact on microbial loads was evaluated by traditional plate count methods, while morphological changes were determined using scanning electron microscopy (SEM). Physiological property changes were obtained through flow cytometric measurements (membrane integrity, esterase activity and membrane potential). In addition, mathematical modelling was performed in order to achieve a reliable prediction of microbial inactivation and to establish the basis for possible industrial implementation. C. freundii loads in apple juice were reduced by about 5 log cycles after a plasma exposure of 480s using argon and 0.1% oxygen plus a subsequent storage time of 24h. The results indicate that a direct contact between bacterial cells and plasma is not necessary for achieving successful inactivation. The plasma-generated compounds in the liquid, such as H2O2 and most likely hydroperoxy radicals, are particularly responsible for microbial inactivation.