Direct Plasma Exposure Research Articles

Comparative effects of direct plasma treatment and plasma-activated media on B16F10 cancer cells using a multipoint surface dielectric barrier discharge system

Abstract Cancer remains a leading cause of mortality worldwide, necessitating novel, effective, and selective therapies. Cold Atmospheric Plasma (CAP) generates reactive species that can selectively kill tumor cells while sparing healthy tissue. We developed a multipoint Surface Dielectric Barrier Discharge (SDBD) plasma system capable of simultaneously treating all wells in a 24-well plate, enhancing experimental throughput and consistency. We investigated both direct plasma treatment and indirect effects via plasma-activated media (PAM) on the viability of B16F10 melanoma cells and L929 fibroblasts. Characterizations confirmed uniform plasma generation and safe operating temperatures suitable for cell applications. Physicochemical analyses of PAMs showed time-dependent changes in pH, oxidation-reduction potential, and conductivity, indicating the generation of reactive species like nitrite, nitrate, and hydrogen peroxide. Cytotoxicity assays demonstrated that both direct plasma treatment and PAM significantly reduced melanoma cell viability, with direct treatment causing a more pronounced effect. After 3 minutes of direct exposure, melanoma cell viability decreased to approximately 30% after 24 hours and further to 13% after 48 hours. In contrast, healthy L929 fibroblasts remained largely unaffected under both treatment conditions. These results suggest that both short-lived and long-lived reactive species contribute to the selective cytotoxic effects observed in cancer cells. The multipoint SDBD plasma system shows potential as a selective anticancer treatment modality, effective through both direct plasma exposure and the application of PAM, offering a promising avenue for future cancer therapies.

Near-Plasma Chemical Surface Engineering.

As a new trend in plasma surface engineering, plasma conditions that allow more-defined chemical reactions at the surface are being increasingly investigated. This is achieved by avoiding high energy deposition via ion bombardment during direct plasma exposure (DPE) causing destruction, densification, and a broad variety of chemical reactions. In this work, a novel approach is introduced by placing a polymer mesh with large open area close to the plasma-sheath boundary above the plasma-treated sample, thus enabling near-plasma chemistry (NPC). The mesh size effectively extracts ions, while reactive neutrals, electrons, and photons still reach the sample surface. The beneficial impact of this on the plasma activation of poly (tetrafluoroethylene) (PTFE) to enhance wettability and on the plasma polymerization of siloxanes, combined with the etching of residual hydrocarbons to obtain highly porous SiOx coatings at low temperatures, is discussed. Characterization of the treated samples indicates a predominant chemical modification yielding enhanced film structures and durability.

Increased Expression of ITGB 3 in CLL Patient leukemia Cells by Exposure to Cold Physical Plasma and Plasma-treated Medium.

Chronic lymphocytic leukemia (CLL) is the most prevalent hematological cancer, with various medical interventions. In the recent decade, cold physical plasma has become an interesting agent for future cancer therapy. The goal of this study was to see whether cold physical plasma or cold physical plasma-treated liquid (PTL) affected integrin beta 3 (ITGB3) expression, which is hypothesized to mediate an interaction between cancer stem cells and the bone marrow microenvironment, in CLL patients' blood cells. The metabolic activity, cell death pattern, lipid oxidation and ITGB3 gene expression of these treatments was evaluated. Both direct cold physical plasma and PTL exposure enhanced lipid peroxidation in cells of CLL patients, but to a lesser extent in healthy participants. Furthermore, following 48h of cold physical plasma or PTL exposure, the metabolic activity of leukocytes was preferentially reduced in CLL patient leukocytes. In addition, cold physical plasma and PTL treatment elevated ITGB3 mRNA expression in CLL patients' leukocytes compared to untreated and healthy controls. Collectively, our study suggests selective effects of direct cold physical plasma and PTL exposure on blood leukocytes from leukemia patients, but further and more detailed studies are needed to provide additional rationales for such treatment options as future therapy.

Polymerization mechanisms of hexamethyldisiloxane in low-pressure plasmas involving complex geometries

Hexamethyldisiloxane (HMDSO) low-pressure plasmas are known for their versatility in the deposition of plasma polymer films (PPFs) with different properties and applications. Although they have been studied for decades, the reaction mechanisms of plasma polymer formation leave open questions, particularly when deposition on 3D materials with complex geometries such as cavities and undercuts is considered. In the present study, two configurations named “cavity” and “undercut” have been selected to study the influence of diffusion of film-forming species and surface reactivity in HMDSO plasmas without and with O2 admixture. A varying spatial chemical composition of the plasma polymer deposit along the penetration depth of the studied configurations indicates different sticking probabilities of the film-forming species. Furthermore, although ion-induced effects are usually only considered for direct plasma exposure, the obtained results and additional etching experiments reveal that the contribution of high-energy particles might still be considered underneath small openings. Finally, the relevance of oxidizing chemical reactions at the surface inside the configurations is clarified when O2 is added to the plasma.

Combined effects of direct plasma exposure and pre-plasma functionalized metal-doped graphene oxide nanoparticles on wastewater dye degradation

The current study investigates the combinatorial effect of the photocatalytic performance of plasma pre-treated Ti-Cu-Zn doped graphene oxide (TCZ-GO) nanoparticles (NPs) and advanced oxidation processes of a non-thermal atmospheric pressure plasma on the degradation of reactive orange-122 (RO-122) dye compounds. Firstly, in order to enhance the photocatalytic performance of the synthesized composite NPs, they were subjected to glow discharge plasma treatments operating in different gases (Ar, air, O2 and N2). Their surface morphology, chemical composition and band gap were examined by means of scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and UV–Vis spectrophotometry respectively. XPS results revealed that plasma-treated NPs exhibited a higher content of oxygen vacancies and a variation in their oxidation states (Ti4+ → Ti3+, Cu+ → Cu2+). These plasma-induced surface chemical changes hindered the recombination of photo-generated electron-hole pairs which led to a drop in the bandgap of the NPs with N2 plasma-treated NPs acquiring the lowest bandgap. Lastly, the article examined the actual decomposition of RO-122 dye in wastewater by an Ar plasma treatment alone or combined with the plasma-treated TCZ-GO NPs via spectrophotometric analyses, electrical conductivity, pH and total organic carbon (TOC) removal measurements. Moreover, the reactive species produced during the combined plasma/photocatalysis induced degradation were detected in situ by optical emission spectroscopy. Results revealed that the processes carried out by combining N2 plasma-treated TCZ-GO NPs and Ar plasma exhibited the highest degradation efficiency (85 %) due to the generation of more OH and H2O2. Overall, it can be concluded that plasma-aided treatment processes used synergistically as indirect surface functionalization of TCZ-GO NPs and direct plasma treatment of wastewater are extremely efficient in the degradation of toxic compounds and can be extrapolated to various environmental applications.

Cytotoxicity of Nonthermal Plasma Treatments on Three Cancer Cell Lines Induces Changes in Cell Morphology and in HSP70 Gene Expression

Nonthermal plasma processes recently emerged as promising therapeutic tools for the treatment of cancer. Most anticancer effects of plasma have been related to the induction of oxidative stress due to the release of reactive oxygen and nitrogen species (RONS), among other plasma components, during discharge. The exact mechanism of action in the eradication of cancer, though, is still far from being fully understood. In this research, three cancer-derived cell lines were exposed to pulsed dielectric barrier discharge (DBD) to investigate the effect of direct plasma exposure on cancer cells. Among many cellular functions, cell adhesion and morphology were found to be visibly influenced. Morphological assays showed the inhibition of intercellular adhesion, losses in cell clustering, and changes in the external shape and actin cytoskeleton. These effects were related to the decrease in cell viability and plasma operational conditions. The increased expression of the heat shock protein HSP70 in plasma-exposed Saos2 cells confirmed that changes in morphology and viability in cancer cells are representative of internal changes in the oxidative state of cells that are caused by plasma-induced oxidative stress.

Performance of a high vacuum, high temperature compatible millimeter-range viewing dump for the vertical ECE experiment on TCV

A high vacuum and high temperature compatible viewing dump, made of MACOR, was designed and installed in TCV for Vertical ECE experiments in the 75–110 GHz frequency range. Measurements of the dump prior to installation in the tokamak showed in more than 99 % of absorption of the incoming radiation. The dump has remained in-vessel more than 7 years, protected from direct plasma exposure by carbon tiles. However it has still been exposed to carbon and boron deposition. Very recently, ex-vessel and in-vessel measurements were carried out over an extended frequency range up to 170 GHz to assess the change in performance of the dump due to exposure in the Tokamak. The new results show that the dump performance has not been adversely affected by seven years of in-vessel exposure and in fact match the original measurements, showing that the dump is still suitable for Vertical ECE experiments on TCV.

Effects of cold plasma on wheat grain microbiome and antimicrobial efficacy against challenge pathogens and their resistance

The safety and quality of cereal grain supplies are adversely impacted by microbiological contamination, with novel interventions required to maximise whole grains safety and stability. The microbiological contaminants of wheat grains and the efficacy of Atmospheric Cold Plasma (ACP) for potential to control these risks were investigated. The evaluations were performed using a contained reactor dielectric barrier discharge (DBD) system; samples were treated for 0–20 min using direct and indirect plasma exposure. Amplicon-based metagenomic analysis using bacterial 16S rRNA gene and fungal 18S rRNA gene with internal transcribed spacer (ITS) region was performed to characterize the change in microbial community composition in response to ACP treatment. The antimicrobial efficacy of ACP against a range of bacterial and fungal contaminants of wheat, was assessed to include individual isolates from grains as challenge pathogens. ACP influenced wheat microbiome composition, with a higher microbial diversity as well as abundance found on the untreated control grain samples. Culture and genomic approaches revealed different trends for mycoflora detection and control. A challenge study demonstrated that using direct mode of plasma exposure with 20 min of treatment significantly reduced the concentration of all pathogens. Overall, reduction levels for B. atrophaeus vegetative cells were higher than for all fungal species tested, whereas B. atrophaeus spores were the most resistant to ACP among all microorganisms tested. Of note, repeating sub-lethal plasma treatment did not induce resistance to ACP in either B. atrophaeus or A. flavus spores. ACP process control could be tailored to address diverse microbiological risks for grain stability and safety.

MOS Capacitance Measurements for PEALD TiO2 Dielectric Films Grown under Different Conditions and the Impact of Al2O3 Partial-Monolayer Insertion.

In this paper, we report the plasma-enhanced atomic layer deposition (PEALD) of TiO2 and TiO2/Al2O3 nanolaminate films on p-Si(100) to fabricate metal-oxide-semiconductor (MOS) capacitors. In the PEALD process, we used titanium tetraisopropoxide (TTIP) as a titanium precursor, trimethyl aluminum (TMA) as an aluminum precursor and O2 plasma as an oxidant, keeping the process temperature at 250 °C. The effects of PEALD process parameters, such as RF power, substrate exposure mode (direct or remote plasma exposure) and Al2O3 partial-monolayer insertion (generating a nanolaminate structure) on the physical and chemical properties of the TiO2 films were investigated by Rutherford backscattering spectroscopy (RBS), Raman spectroscopy, grazing incidence X-ray diffraction (GIXRD), and field emission scanning electron microscopy (FESEM) techniques. The MOS capacitor structures were fabricated by evaporation of Al gates through mechanical mask on PEALD TiO2 thin film, followed by evaporation of an Al layer on the back side of the Si substrate. The capacitors were characterized by current density-voltage (J-V), capacitance-voltage (C-V) and conductance-voltage (G-V) measurements. Our results indicate that RF power and exposure mode promoted significant modifications on the characteristics of the PEALD TiO2 films, while the insertion of Al2O3 partial monolayers allows the synthesis of TiO2/Al2O3 nanolaminate with well-spaced crystalline TiO2 grains in an amorphous structure. The electrical characterization of the MOS structures evidenced a significant leakage current in the accumulation region in the PEALD TiO2 films, which could be reduced by the addition of partial-monolayers of Al2O3 in the bulk of TiO2 films or by reducing RF power.

Applications of plasma-enhanced metalorganic chemical vapor deposition

Abstract The use of plasma enhancement for growth of III-V compound semiconductor materials by metalorganic chemical vapor deposition (MOCVD) is examined, to improve control of microstructure, develop understanding of the underlying growth mechanisms, and expand the range of materials combinations for photovoltaic and solid-state lighting applications. Whereas plasma is commonly used with group-IV materials, such as silicon, few studies have examined the impact of plasma-enhanced MOCVD (PE-MOCVD) for III-V materials growth. PE-MOCVD provides improved decomposition of metalorganic precursors, which is driven by hydrogen plasma to augment hydride reactions and thermal pyrolysis, but plasma generation requires low reactor pressure. We have demonstrated elemental Al films grown by PE-MOCVD, which show distinct crystallographic texturing, and assume epitaxial microstructure upon post-growth annealing. We also demonstrate PE-MOCVD of GaAs at temperatures as low as 300 °C. With increasing radio-frequency power, the GaAs growth rate shows a transition from power limited to mass-transport limited. PE-MOCVD grown Ga0.5In0.5P shows no detectable spontaneous atomic ordering, which offers a mechanism to form order/disorder unicompositional heterostructures, without temperature change or impurity incorporation. In its current implementation, PE-MOCVD grown films have shown microstructural degradation, that we attribute to direct plasma exposure during growth. Improvements in the system design and growth sequences are at the focus of on-going efforts.

In vitro comparison of direct plasma treatment and plasma activated water on Escherichia coli using a surface micro-discharge

In this study, our aim is to compare the inactivation of bacteria by direct plasma exposure of bacterial solution and plasma activated water (PAW) using a surface micro-discharge (SMD). Four potential factors which could affect both treatments were tested, namely the effect of low dose reactive oxygen species (ROS) pretreatment, enzymatic defence mechanism against oxidative stress, extracellular molecules, and mass transfer in liquid. We applied two power modes of the SMD, i.e. low power ozone mode and high power mode, to inactivate () in distilled water either by direct treatment (DT) or PAW. ROS pretreatment was tested by 30 M of , while superoxide dismutase (SOD) and catalase were used to investigate the effect of enzymatic antioxidant defense. Furthermore, the effect of extracellular molecules was examined by centrifuging and mass transfer in liquid by vortexing. In addition, reactive species in the solution were measured by titanium sulfonate, and nitrite/nitrate colorimetric method for , and and , respectively. Results indicate that vortexing and centrifuging significantly influence the bacterial reduction, while pretreatment could not induce resistance of bacteria against plasma treatment. Enzymatic antioxidants of SOD and catalase could potentially effect the inactivation and plasma chemistry yet only if the concentrations are sufficiently high. We assume that the continuous generation of peroxynitrite is crucial in plasma inactivation for both DT and PAW under high power condition, while under low power condition, long-term bactericidal affects are limited due to the decomposition of ozone by nitrite.

Effect of Plasma Activated Mist on Breast Cancer Cells

Plasma activated mist (PAMI) is generated by tiny water vapor droplets passing through cold atmospheric plasma discharge. The effect of PAMI is compared to direct plasma exposure during treatment of breast cancer cells MCF-7. The direct plasma jet is operated with argon gas while the PAMI discharge is operated through ambient air and flowing mist. Both discharges are directed to cultured cells. Plasma is generated by an ac signal in KHz range. Mist with water droplets of 30 ${\mu }\text{m}$ in diameter with addition of few drops of hydrogen peroxide is generated by an ultrasonic nebulizer. Cell viability and reactive oxygen species production are measured under argon plasma and PAMI in adherent treated cultured MCF-7 cells. After few minutes treatment time, percentage of viable cells goes down while percentage of apoptotic cells increases. This phenomena is enhanced with the application of indirect PAMI compared to direct argon plasma.

Formation of lateral chemical gradients in plasma polymer films shielded by an inclined mask

Low pressure plasma deposition conditions are investigated yielding oxygen‐containing lateral gradient coatings (aC:H:O) by means of an inclined static mask partly shielding the substrate. Such lateral gradient coatings are formed by the diffusion of film‐forming species with different reactivities underneath the mask. Surface characterization revealed varying film growth conditions below the mask different from direct plasma exposure with increasing distance from the mask/plasma edge: i) exponentially decreasing film growth; ii) decreasing roughness following the thickness trend; iii) decreasing hydrophilicity; iv) variation in cross‐linking; and v) different chemical composition. Oxygen‐rich film‐forming species appeared to react closer to the mask/plasma edge, while oxygen‐poor film‐forming species can diffuse deeper, leading to a pronounced gradient in chemical composition and in cross‐linking in the masked area.

Plasma-Activated Medium Inhibites Metastatic Activities Of Ovarian Cancer Cells In Vitro Via Repressing Mapk Pathway

Ovarian cancer is among the most malignant gynecologic cancers since peritoneal dissemination often occurs at the diagnosis of these patients. The 5-year survival rate is less than 50%. Recently, non-equilibrium atmospheric pressure plasma (NEAPP) has been introduced in medical field. We have already demonstrated the cytotoxic effect of the direct plasma exposure to ovarian cancer cells. However, it is difficult to expose cancer cells to plasma gas intraperitoneally. Thus, we established the system of plasma-activated medium (PAM) to treat ovarian cancer indirectly instead of a direct exposure to plasma [1]. In our previous works, it was demonstrated that PAM significantly inhibited proliferation ability of ovarian cancer cells, with fibroblast cells remaining unaffected though. Both in vitro and in vivo study had confirmed the cytotoxic effect of PAM to ovarian cancer. However, it still remains unknown whether PAM can affect metastasis of ovarian cancer cells, which is the fatal problem of ovarian cancer patients [2]. In this study, we tried to investigate PAM’s anti-metastasis effect in vitro and the underneath mechanism. Firstly, we performed wound-healing and transwell assay on ES2, one of ovarian cancer cell lines. We found that the cell migration and invasion abilities were significantly inhibited by PAM. Secondly, we established a co-culture system by seeding ES2 cells onto monolayer of peritoneal mesothelial cells, which models the initial step of ovarian cancer cells metastasis in human peritoneal cavity, and it was found that PAM significantly repressed ES2 cells to implant onto mesothelial cells. Moreover, mechanism study showed both mRNA and protein levels of MMP-9 were inhibited by PAM. And PAM significantly inhibited the phosphorylation of JNK1/2 MAPK and p38 MAPK (figure 1), which indicated that inhibition of MMP-9 was dependent on MAPK pathway [3]. In summary, it is indicated in this work that PAM presents efficient inhibitory effect towards ovarian cancer cells metastasis in vitro. Moreover, PAM’s anti-metastasis effect is implemented by repressing the activation MAPK pathway, resulting in de-activation of downstream target MMP-9, thus leading to suppression of cell migration and invasion. In the near future, it might be a new clinical strategy for metastatic ovarian cancer patients to choose PAM therapy via intaperitoneal treatment. Download : Download high-res image (86KB) Download : Download full-size image Fig. 1

Plasma-wall interaction studies in the full-W ASDEX upgrade during helium plasma discharges

Plasma-wall interactions have been studied in the full-W ASDEX Upgrade during its dedicated helium campaign. Relatively clean plasmas with a He content of >80% could be obtained by applying ion cyclotron wall conditioning (ICWC) discharges upon changeover from D to He. However, co-deposited layers with significant amounts of He and D were measured on W samples exposed to ICWC plasmas at the low-field side (outer) midplane. This is a sign of local migration and accumulation of materials and residual fuel in regions shadowed from direct plasma exposure albeit globally D was removed from the vessel. When exposing W samples to ELMy H-mode helium plasmas in the outer strike-point region, no net erosion was observed but the surfaces had been covered with co-deposited layers mainly consisting of W, B, C, and D and being the thickest on rough and modified surfaces. This is different from the typical erosion-deposition patterns in D plasmas, where usually sharp net-erosion peaks surrounded by prominent net-deposition maxima for W are observed close to the strike point. Moreover, no clear signs of W nanostructure growth or destruction could be seen. The growth of deposited layers may impact the operation of future fusion reactors and is attributed to strong sources in the main chamber that under suitable conditions may switch the balance from net erosion into net deposition, even close to the strike points. In addition, the absence of noticeable chemical erosion in helium plasmas may have affected the thickness of the deposited layers. Retention of He, for its part, remained small and uniform throughout the strike-point region although our results indicate that samples with smooth surfaces can contain an order of magnitude less He than their rough counterparts.

Bactericidal Effects of Plasma Induced Reactive Species in Dielectric Barrier Gas–Liquid Discharge

An atmospheric helium dielectric barrier discharge is used to treat Staphylococcus aureus (S. aureus) to study plasma bacteria inactivation in the gas–liquid phase. Optical emission spectroscopy, mass spectrometry, and spectrophotometry are used to analyze the products induced by the plasma in the liquid as well as interactions between the liquid products and bacteria. The bactericidal mechanisms associated with the liquid products and different treatment protocols are investigated. The short-lived reactive species produce efficient inactivation effects in the direct plasma treatment and long-lived reactive species show continuous residual bactericidal effects. Additionally, even the minor initial damage caused by direct plasma exposure promotes the residual inactivation effect. After the discharge treatment for 1, 3, 5, and 8 min, the initial damage causes residual bacterial inactivation of 9.3, 37.2, 81.8, and 86.7%, respectively. Meanwhile, the discharge time and storage time in the different treatment processes can be optimized to achieve better bactericidal efficiency and energy efficiency. The results provide insights into the future development of plasma medicine and water purification.

Sorbent track: Quantitative monitoring of adsorbed VOCs under in-situ plasma exposure.

Sorbent-TRACK is a new device developed to monitor adsorption and surface oxidation of pollutants under direct plasma exposure. It is based on direct transmitted Fourier Transformed Infrared (FTIR) spectroscopy. A pyrex reactor under controlled gas pressure and composition is inserted on the infrared beam of a commercially available Nicolet 5700 FTIR spectrometer. A substrate holder is located on the optical path of the infrared beam. A thin pellet of a dedicated catalyst (CeO2 in the present work) is inserted in a substrate holder and can be exposed to direct plasma treatment using a Dielectric Barrier Discharge. The time resolution of Sorbent-TRACK is limited by the time resolution of the Nicolet 5700 FTIR spectrometer and close to 30 s. The dynamic of the adsorption and plasma oxidation of acetone and isopropanol on CeO2 are studied and intermediates are monitored. Performances and sensitivity of Sorbent-TRACK are reported Adsorption and oxidation of acetone leads to production of adsorbed isobutene and acetic acid, where oxidation of isopropanol gives mainly to adsorbed acetone, mesityl oxide and acetate. An increase of the plasma power leads to an increase of the isopropanol and acetone oxidation rate and a related increase of the production of adsorbed intermediates.

Relationships among growth mechanism, structure and morphology of PEALD TiO2 films: the influence of O2 plasma power, precursor chemistry and plasma exposure mode

Titanium dioxide (TiO2) thin films have generated considerable interest over recent years, because they are functional materials suitable for a wide range of applications. The efficient use of the outstanding functional properties of these films relies strongly on their basic characteristics, such as structure and morphology, which are affected by deposition parameters. Here, we report on the influence of plasma power and precursor chemistry on the growth kinetics, structure and morphology of TiO2 thin films grown on Si(100) by plasma-enhanced atomic layer deposition (PEALD). For this, remote capacitively coupled 13.56 MHz oxygen plasma was used to act as a co-reactant during the ALD process using two different metal precursors: titanium tetrachloride (TiCl4) and titanium tetraisopropoxide (TTIP). Furthermore, we investigate the effect of direct plasma exposure during the co-reactant pulse on the aforementioned material properties. The extensive characterization of TiO2 films using Rutherford backscattering spectroscopy, ellipsometry, x-ray diffraction (XRD), field-emission scanning electron microscopy, and atomic force microscopy (AFM) have revealed how the investigated process parameters affect their growth per cycle (GPC), crystallization and morphology. The GPC tends to increase with plasma power for both precursors, however, for the TTIP precursor, it starts decreasing when the plasma power is greater than 100 W. From XRD analysis, we found a good correlation between film crystallinity and GPC behavior, mainly for the TTIP process. The AFM images indicated the formation of films with grain size higher than film thickness (grain size/film thickness ratio ≈20) for both precursors, and plasma power analysis allows us to infer that this phenomenon can be directly related to the increase of the flux of energetic oxygen species on the substrate/growing film surface. Finally, the effect of direct plasma exposure on film structure and morphology was evidenced showing that the grid removal causes a drastic reduction in the grain size, particularly for TiO2 synthesized using TiCl4.

Influence of high voltage atmospheric cold plasma process parameters and role of relative humidity on inactivation of Bacillus atrophaeus spores inside a sealed package

Non-thermal plasma has received much attention for elimination of microbial contamination from a range of surfaces. This study aimed to determine the effect of a range of dielectric barrier discharge high voltage atmospheric cold plasma (HVACP) parameters for inactivation of Bacillus atrophaeus spores inside a sealed package. A sterile polystyrene Petri dish containing B.atrophaeus spore strip (spore population 2.3×10(6)/strip i.e. 6.36 log10/strip) was placed in a sealed polypropylene container and was subjected to HVACP treatment. The HVACP discharge was generated between two aluminium plate electrodes using a high voltage of 70kVRMS. The effects of process parameters, including treatment time, mode of exposure (direct/indirect), and working gas types, were evaluated. The influence of relative humidity on HVACP inactivation efficacy was also assessed. The inactivation efficacy was evaluated using colony counts. Optical absorption spectroscopy (OAS) was used to assess gas composition following HVACP exposure. A strong effect of process parameters on inactivation was observed. Direct plasma exposure for 60s resulted in ≥6 log10 cycle reduction of spores in all gas types tested. However, indirect exposure for 60s resulted in either 2.1 or 6.3 log10 cycle reduction of spores depending on gas types used for HVACP generation. The relative humidity (RH) was a critical factor in bacterial spore inactivation by HVACP, where a major role of plasma-generated species other than ozone was noted. Direct and indirect HVACP exposure for 60s at 70% RH recorded 6.3 and 5.7 log10 cycle reduction of spores, respectively. In summary, a strong influence of process parameters on spore inactivation was noted. Rapid in-package HVACP inactivation of bacterial spores within 30-60s demonstrates the promising potential application for reduction of spores on medical devices and heat-sensitive materials.

Cold Air Plasma To Decontaminate Inanimate Surfaces of the Hospital Environment

The hospital environment harbors bacteria that may cause health care-associated infections. Microorganisms, such as multiresistant bacteria, can spread around the patient's inanimate environment. Some recently introduced biodecontamination approaches in hospitals have significant limitations due to the toxic nature of the gases and the length of time required for aeration. This study evaluated the in vitro use of cold air plasma as an efficient alternative to traditional methods of biodecontamination of hospital surfaces. Cultures of methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), extended-spectrum-β-lactamase (ESBL)-producing Escherichia coli, and Acinetobacter baumannii were applied to different materials similar to those found in the hospital environment. Artificially contaminated sections of marmoleum, mattress, polypropylene, powder-coated mild steel, and stainless steel were then exposed to a cold air pressure plasma single jet for 30 s, 60 s, and 90 s, operating at approximately 25 W and 12 liters/min flow rate. Direct plasma exposure successfully reduced the bacterial load by log 3 for MRSA, log 2.7 for VRE, log 2 for ESBL-producing E. coli, and log 1.7 for A. baumannii. The present report confirms the efficient antibacterial activity of a cold air plasma single-jet plume on nosocomial bacterially contaminated surfaces over a short period of time and highlights its potential for routine biodecontamination in the clinical environment.