Evaluation of cold atmospheric plasma for the decontamination of flexible endoscopes.

BACKGROUND: Despite adherence to standard protocols, residues including live micro-organisms may remain on the various surfaces of reprocessed flexible endoscopes. Prions are infectious proteins that are notoriously difficult to eliminate. AIM: To test the potential of cold atmospheric plasma (CAP) for the decontamination of various surfaces of flexible endoscopes, measuring total proteins and prion residual infectivity as indicators of efficacy. METHODS: New PTFE endoscope channels and metal test surfaces spiked with test soil or prion-infected tissues were treated using different CAP-generating prototypes. Surfaces were examined for the presence of residues using very sensitive fluorescence epimicroscopy. Prion residual infectivity was determined using the wire implant animal model and a more sensitive cell infectivity assay. FINDINGS: A CAP jet applied perpendicularly at close range on flat test surfaces removed soil within 3 min, but left microscopic residues and failed to eliminate prion infectivity according to the wire implant animal assay. The longitudinal gas flow from CAP prototypes developed for the treatment of long channels led to the displacement and sedimentation of residual soil towards the distal end, when applied alone. Observations of the plasma inside glass tubes showed temporal and spatial heterogeneity within a limited range. After the standard enzymatic manual pre-wash, 'CAP-activated' gas effluents prevented prion transmission from treated endoscope channels according to the prion infectivity cell assay. CONCLUSION: CAP shows promising results as a final step for decontamination of surgical surfaces. Optimizing CAP delivery could further enhance CAP efficacy, offering a safe, chemical-free alternative for the reprocessing of all luminal flexible endoscope surfaces.

Effect of microscope parameter and specimen thickness of spatial resolution of transmission electron backscatter diffraction.

The spatial resolution of transmission electron backscatter diffraction (t-EBSD) with a standard conventional EBSD detector was evaluated quantitatively based on the calculation of the correlation coefficient of transmission patterns which were acquired across a twin boundary in the sample of austenitic steel. The results showed that the resolution of t-EBSD improved from tens of nanometres to below 10 nm with increasing accelerating voltage and thinning of specimen thickness. High voltage could enhance the penetration depth and reduce the scattering angle. And the thinning of specimen thickness would result in decreasing of the scattering events according to the theory of thermal diffuse scattering (TDS). In addition, the transmission patterns were found to be weak and noisy if the specimen was too thin, because of the decreasing intensity detected by the screen. Consequently, in this work, the best spatial resolution of 7 nm was achieved at 30 kV and 41 nm thickness. Moreover, the specimen thickness range was also discussed using Monte-Carlo simulation. This approach was helpful to account for the differences of measured spatial resolutions, by t-EBSD, of lamellas with different thickness.

Aqueous reactive species induced by a surface air discharge: Heterogeneous mass transfer and liquid chemistry pathways.

Plasma-liquid interaction is a critical area of plasma science and a knowledge bottleneck for many promising applications. In this paper, the interaction between a surface air discharge and its downstream sample of deionized water is studied with a system-level computational model, which has previously reached good agreement with experimental results. Our computational results reveal that the plasma-induced aqueous species are mainly H(+), nitrate, nitrite, H2O2 and O3. In addition, various short-lived aqueous species are also induced, regardless whether they are generated in the gas phase first. The production/loss pathways for aqueous species are quantified for an air gap width ranging from 0.1 to 2 cm, of which heterogeneous mass transfer and liquid chemistry are found to play a dominant role. The short-lived reactive oxygen species (ROS) and reactive nitrogen species (RNS) are strongly coupled in liquid-phase reactions: NO3 is an important precursor for short-lived ROS, and in turn OH, O2(-) and HO2 play a crucial role for the production of short-lived RNS. Also, heterogeneous mass transfer depends strongly on the air gap width, resulting in two distinct scenarios separated by a critical air gap of 0.5 cm. The liquid chemistry is significantly different in these two scenarios.

Surface air plasma-induced cell death and cytokine release of human keratinocytes in the context of psoriasis.

BACKGROUND: Cold atmospheric plasma (CAP) has shown promise for wound healing, although little is understood of the underpinning mechanisms. Little has been reported so far of its potential use in the treatment of immune-mediated diseases such as psoriasis. OBJECTIVES: To study CAP-induced cell death and cytokine release in human keratinocytes as a first assessment of possible CAP use for psoriasis. METHODS: Using a CAP generator free of energetic ions, we observed its effects on keratinocytes in terms of morphology, cell viability and apoptosis, intracellular and mitochondrial reactive oxygen species (ROS), lysosomal integrity and mitochondrial membrane potential; and on secretion and expression of eight cytokines at protein and gene levels. RESULTS: CAP-induced reduced cell viability, apoptotic death and production of intracellular and mitochondrial ROS in dose-dependent manner. Mitochondrial dysfunction and lysosomal leakage were found in CAP-treated cells. It also induced release of interleukin (IL)-6, IL-8, tumour necrosis factor (TNF)-α and vascular endothelial growth factor (VEGF), and enhanced the mRNA expression of IL-1ß, IL-6, IL-8, IL-10, TNF-α, interferon-γ and VEGF. By contrast, IL-12 declined monotonically. CONCLUSIONS: The results suggest that with appropriate control of its dose, physical plasma could induce cell death via apoptotic pathways and enable simultaneous reduction in IL-12. These effects may be used to suppress keratinocyte hyperproliferation and to target T-cell activation to control amplification of inflammation. This provides an initial basis for further studies of CAP as a potential therapeutic option for inflammatory and immune-related diseases in dermatology, including psoriasis.

Cold atmospheric plasma disinfection of cut fruit surfaces contaminated with migrating microorganisms.

The efficacy of cold atmospheric gas plasmas against Escherichia coli type 1, Saccharomyces cerevisiae, Gluconobacter liquefaciens, and Listeria monocytogenes Scott A was examined on inoculated membrane filters and inoculated fruit surfaces. Inoculated samples were exposed to a cold atmospheric plasma plume generated by an AC voltage of 8 kV at 30 kHz. The cold atmospheric plasma used in this study was very efficient in reducing the microbial load on the surfaces of filter membranes. However, its efficacy was markedly reduced for microorganisms on the cut surfaces. This lack of effect was not the result of quenching of reactive plasma species responsible for microbial inactivation but principally the result of the migration of microorganisms from the exterior of the fruit tissue to its interior. The velocity of migration through melon tissues was estimated to be around 300 microm min(-1) for E. coli and S. cerevisiae and through mango tissues to be 75 to 150 microm min(-1). These data can serve as operational targets for optimizing the performance of gas plasma inactivation processes. The current capabilities of cold atmospheric plasmas are reviewed and ways to improve their bactericidal efficacy are identified and discussed. Considerable scope exists to enhance significantly the efficacy of cold atmospheric plasmas for decontaminating fresh cut fruits.

Bacterial cells exposed to nanosecond pulsed electric fields show lethal and sublethal effects.

Cell suspensions of Escherichia coli K12 and Salmonella typhimurium were exposed to electrical pulses of 32 ns duration at a field intensity of 100 kV/cm and a repetition rate of 30 pulses per second for a total of 300 s. Treated cells were plated onto Tryptone Soya Agar (TSA) and TSA supplemented with NaCl, and cell counts were monitored daily for 3 days. The concentrations of NaCl used were 3 and 4% (w/v) for E. coli and 4 and 5% (w/v) for S. typhimurium. Treatment under these conditions resulted in a 2 log(10) reduction for E. coli and approximately a single log(10) reduction for S. typhimurium. For both species of bacteria it was discovered that the surviving population was composed of only 1% of uninjured cells. Moreover, the proportion of sublethally injured cells increased more rapidly than the total recoverable population suggesting a process of injury accumulation culminating in death rather than an 'all or nothing' mechanism. Sublethal injury manifested itself in a proportion of the injured population of both species by an extended lag phase at longer treatment times. Finally, possible mechanisms by which nanosecond electric pulses inactivate bacteria are discussed.

Electron kinetics in radio-frequency atmospheric-pressure microplasmas.

The kinetic study of three radio-frequency atmospheric-pressure helium microdischarges indicates that the electron energy probability function is far from equilibrium, and three electron groups with three distinct temperatures are identified. The relative population of electrons in different energy regions is strongly time modulated and differs significantly from values recently reported from fluid analyses. It is also shown that a flux of energetic electrons (epsilon>5 eV) that comprises up to 50% of the total electron flux can reach the electrodes. This energetic electron flux provides a new means of delivering energy to the electrodes and tuning the surface chemistry in atmospheric-pressure discharges. The three electron groups and the engineering of an energetic electron flux might open up a new paradigm in plasma-surface chemistry that has not been considered up until now.

Effects of cell surface loading and phase of growth in cold atmospheric gas plasma inactivation of Escherichia coli K12.

AIMS: To determine the effects of surface cell concentration and phase of growth on the inactivation of Escherichia coli cells using an atmospheric nonthermal plasma. METHODS AND RESULTS: Cells of E. coli K12 were deposited onto the surface of membrane filters and exposed to the plume from a cold atmospheric gas plasma. Scanning electron microscopy revealed severe loss in structural integrity of plasma-treated cells, and optical emission spectra indicated that inactivation was brought about by reactive plasma species. The survival of E. coli cells was found to depend on the cell surface density: as the surface density increased from 10(7) to 10(11) CFU cm(-2), the rate constant in the Baranyi inactivation model decreased from 19.59 to 1.03 min(-1). Cells harvested from mid-exponential, late exponential and stationary phases of growth displayed differences in their resistances to the effects of the plasma however, exponential phase cells were not more susceptible than those from the stationary phase. CONCLUSIONS: High surface concentrations of cells affects the penetration of plasma species and treatment effectiveness. The physiological state of cells, as determined by phase of growth, affects their resistance to plasma inactivation. SIGNIFICANCE AND IMPACT OF THE STUDY: In designing inactivation treatments, surface concentration and cell physiology need to be taken into account.

Evolution of discharge structure in capacitive radio-frequency atmospheric microplasmas.

Conventional radio-frequency (rf) nonthermal atmospheric plasmas are generated in a millimeter gap. In this Letter, we present a self-consistent numerical study of rf atmospheric microplasmas in a submillimeter gap comparable to their sheath thickness. It is shown that the narrow electrode gap deforms the discharge structure, ultimately removing the bulk-plasma region and disabling electron trapping. Significantly, these properties permit rf atmospheric microplasmas to operate at very high current densities thus simultaneously achieving higher stability and greater chemical reactivity.

Single-crystal CdSe nanowires prepared via vapor-phase growth assisted with silicon.

Hexagonal cadmium selenide (CdSe) nanowires, with diameter around 20 nm, were synthesized using a simple vapor-phase growth. Silicon (Si) powder acts as a source material assisting the synthesis, which is very important to the formation of the CdSe nanowires. We also suggest that self-catalysis at the Cd-terminated (0001) surface, together with the assistance action of Si, leads to the formation of wire-like structures to be formed. Meanwhile, the assistance of Si is responsible for the fineness and uniformity of the CdSe nanowires. The possible growth mechanism of the CdSe nanowires is proposed, and the optical property of the as-grown CdSe nanowires is characterized.