Danil Dobrynin

Physical and biological mechanisms of direct plasma interaction with living tissue

Mechanisms of plasma interaction with living tissues and cells can be quite complex, owing to the complexity of both the plasma and the tissue. Thus, unification of all the mechanisms under one umbrella might not be possible. However, the authors are attempting to make first steps in this direction. In this paper, analysis of interaction of floating electrode dielectric barrier discharge (FE-DBD) with living tissues and cells is presented and biological and physical mechanisms are discussed. In physical mechanisms, charged species are identified as the major contributors to the desired effect and a mechanism of this interaction is proposed. Biological mechanisms are also addressed and a hypothesis of plasma selectivity and its effects is offered.

Inactivation of bacteria using dc corona discharge: role of ions and humidity.

Here we present the results of an experimental study of the effect of ions produced in a dc corona discharge on inactivation of bacteria on the surface of agarose gel. Both positive and negative corona discharges in various gases at different humidities were studied. The measurements in air, O(2), N(2), Ar and He mixtures show that there is no inactivation in pure N(2), pure O(2) and an N(2)-H(2)O mixture. The best results were achieved in the case of direct treatment, when discharge was ignited in oxygen and water-containing mixtures. We show that neither UV radiation, ozone or H(2)O(2) nor other neutral active species alone produced by corona have an effect on bacteria viability. It is shown that the main role of charged particles may be related to the faster transport of active peroxide species-cluster ions OH(-)(H(2)O)(n) and H(3)O(+)(H(2)O)(n). The efficiency of these radicals is much higher than that of the oxygen radicals and ions (including [Formula: see text] and O(3)) and that of nitrogen and argon ions.

Non-equilibrium nanosecond-pulsed plasma generation in the liquid phase (water, PDMS) without bubbles: fast imaging, spectroscopy and leader-type model

In this paper we report the results on study of the non-equilibrium nanosecond discharge generation in liquid media. Here we studied the discharge in both water and silicon transformer oil, and present our findings on discharge behaviour depending on global (applied) electric, discharge emission spectrum and shadow imaging of the discharge. We also discuss possible scenarios of non-equilibrium nanosecond discharge development and suggest that the discharge operates in a leader-type regime supported by the electrostriction effect—creation of nano-sized pores in liquid due to high local electric field.

Direct and controllable nitric oxide delivery into biological media and living cells by a pin-to-hole spark discharge (PHD) plasma

Nitric oxide has great potential for improving wound healing through both inflammatory and vascularization processes. Nitric oxide can be produced in high concentrations by atmospheric pressure thermal plasmas. We measured the physical characteristics and nitric oxide production of a pin-to-hole spark discharge (PHD) plasma, as well as plasma-produced nitric oxide delivery into liquid and endothelial cells. The plasma temperature was calculated as 9030 ± 320 K by the Boltzmann method, which was adequate to produce nitric oxide, although the average gas temperature was near room temperature. The plasma produced significant UV radiation and hydrogen peroxide, but these were prevented from reaching the cells by adding a straight or curved tube extension to the plasma device. Plasma-produced nitric oxide in gas reached 2000 ppm and rapidly diffused into liquid and cells. Cells remained viable following plasma treatment and showed a linear increase in cGMP concentration with plasma treatment, indicating an intracellular functional response to PHD plasma NO. These data suggest that this plasma may provide a novel method for delivering NO locally and directly for enhanced wound healing.

Treatment of raw poultry with nonthermal dielectric barrier discharge plasma to reduce Campylobacter jejuni and Salmonella enterica.

Nonthermal plasma has been shown to be effective in reducing pathogens on the surface of a range of fresh produce products. The research presented here investigated the effectiveness of nonthermal dielectric barrier discharge plasma on Salmonella enterica and Campylobacter jejuni inoculated onto the surface of boneless skinless chicken breast and chicken thigh with skin. Chicken samples were inoculated with antibiotic-resistant strains of S. enterica and C. jejuni at levels of 10(1) to 10(4) CFU and exposed to plasma for a range of time points (0 to 180 s in 15-s intervals). Surviving antibiotic-resistant pathogens were recovered and counted on appropriate agar. In order to determine the effect of plasma on background microflora, noninoculated skinless chicken breast and thighs with skin were exposed to air plasma at ambient pressure. Treatment with plasma resulted in elimination of low levels (10(1) CFU) of both S. enterica and C. jejuni on chicken breasts and C. jejuni from chicken skin, but viable S. enterica cells remained on chicken skin even after 20 s of exposure to plasma. Inoculum levels of 10(2), 10(3), and 10(4) CFU of S. enterica on chicken breast and chicken skin resulted in maximum reduction levels of 1.85, 2.61, and 2.54 log, respectively, on chicken breast and 1.25, 1.08, and 1.31 log, respectively, on chicken skin following 3 min of plasma exposure. Inoculum levels of 10(2), 10(3), and 10(4) CFU of C. jejuni on chicken breast and chicken skin resulted in maximum reduction levels of 1.65, 2.45, and 2.45 log, respectively, on chicken breast and 1.42, 1.87, and 3.11 log, respectively, on chicken skin following 3 min of plasma exposure. Plasma exposure for 30 s reduced background microflora on breast and skin by an average of 0.85 and 0.21 log, respectively. This research demonstrates the feasibility of nonthermal dielectric barrier discharge plasma as an intervention to help reduce foodborne pathogens on the surface of raw poultry.

On the electrostrictive mechanism of nanosecond-pulsed breakdown in liquid phase

In this study we have studied the initial stage of the nanosecond-pulsed discharge development in liquid phase. Modelling predicts that in the case of fast rising strong nonhomogeneous electric fields in the vicinity of high-voltage pin electrode a region saturated with nanoscale non-uniformities may be developed. This phenomenon is attributed to the electrostriction mechanisms and may be used to explain development of breakdown in liquid phase. In this work, schlieren method was used in order to demonstrate formation of negative pressure region in liquids with different dielectric permittivity constants: water, ethanol and ethanol–water mixture. It is shown that this density perturbation, formed at the raising edge of the high-voltage pulse, is followed by a generation of a shock wave propagating with the speed of sound away from the electrode, with negative pressure behind it.

Cold Plasma Inactivation of Bacillus cereus and Bacillus anthracis (Anthrax) Spores

Bacillus spores represent one of the most resistant organisms to conventional sterilization methods. This paper is focused on the inactivation of the spores of two Bacillus species, Bacillus cereus and Bacillus anthracis, using atmospheric-pressure dielectric-barrier-discharge (DBD) plasma. Spores treated in liquid or air-dried on a solid surface were effectively inactivated within 1 min of DBD plasma treatment at a discharge power of 0.3 W/cm2. Results of a series of model experiments show that neutral reactive oxygen species and UV radiation play a dominant role in the inactivation of spores. We also show that 45 s of the DBD plasma treatment of air-dried spores placed inside closed plastic or paper envelopes permits up to 7 log reduction of viable spores.

Reactive Oxygen and Nitrogen Species Production and Delivery Into Liquid Media by Microsecond Thermal Spark-Discharge Plasma Jet

The microsecond spark discharge plasma jet is experimentally analyzed, experimentally and numerical modeling is performed. It is shown that discharge appears as a the number of microdischarges resulting in the average gas temperature of the jet of about 40 ^°C-50 ^°C. Fast imaging and numerical modeling are performed in order to study the discharge development on both microsecond and nanosecond time scales. The biochemical study of the production and the delivery of reactive oxygen and nitrogen species ( H₂O₂, NO, O₂^-, “singlet” oxygen, and ONOO-) into liquid phase is performed using fluorescent dyes.

Investigation of positive and negative modes of nanosecond pulsed discharge in water and electrostriction model of initiation

This work investigates the development of nanosecond pulsed discharges in water ignited with the application of both positive and negative polarity pulses to submerged pin-to-plane electrodes. Optical diagnostics are used to study two main aspects of these discharges: the initiation phase, and the development phase. Nanosecond pulses up to 24 kV with 4 ns rise time, 10 ns duration and 5 ns fall time are used to ignite discharges in a 1.5 mm gap between a copper plate and a tungsten needle with radius of curvature of 25 µm. Fast ICCD imaging is used to trace the discharge development over varying applied pulse amplitudes for both positively and negatively applied pulses to the pin electrode. The discharge is found to progress similar to that of discharges in long gaps—long sparks—in gases, both in structure and development. The more important initiation phase is investigated via schlieren transmission imaging. The region near the tip of the electrode is investigated for slightly under-breakdown conditions, and changes in the liquids refractive index and density are observed over the duration of the applied pulse. An attempt to explain the results is made based on the electrostriction model of discharge initiation.

Initiation stage of nanosecond breakdown in liquid

In this paper, based on a theoretical model (Shneider and Pekker 2013 Phys. Rev. E 87 043004), it has been shown experimentally that the initial stage of development of a nanosecond breakdown in liquids is associated with the appearance of discontinuities in the liquid (cavitation) under the influence of electrostriction forces. Comparison of experimentally measured area dimensions and its temporal development were found to be in a good agreement with the theoretical calculations. This work is a continuation of the experimental and theoretical works (Dobrynin et al 2013 J. Phys. D: Appl. Phys. 46 105201, Starikovskiy 2013 Plasma Sources Sci. Technol. 22 012001, Seepersad et al 2013 J. Phys. D: Appl. Phys. 46 162001, Marinov et al 2013 Plasma Sources Sci. Technol. 22 042001, Seepersad et al 2013 J. Phys. D: Appl. Phys. 46 3555201), initiated by the work in (Shneider et al 2012 IEEE Trans. Dielectr. Electr. Insul. 19 1597–82), in which the electrostriction mechanism of breakdown was proposed.