Priyadarshini Rajasekaran

Biological effects of nitric oxide generated by an atmospheric pressure gas-plasma on human skin cells

Physical plasmas which contain a mixture of different radicals, charged species and UV-radiation, have recently found entry in various medical applications. Though first clinical trials are underway nothing is known about the plasma components mediating the biological effects seen and safety concerns have been neglected. We here use for the first time a plasma device equipped with a bent quartz capillary to omit UV-radiation by directing the gas flux only, containing high concentrations of NO, onto cultured human skin cells. This enables us to compare the effects of plasma produced radical species alone - mainly NO - and in combination with the also emitted UV-radiation on cells. Evaluation of cell death after different treatment times with the capillary present shows no sign of apoptosis in primary human keratinocytes even after 15 min plasma exposure. In human skin endothelial cells however, toxicity is elevated after treatment for more than 10 min. In contrast, without the capillary treatment of both cell types results in maximal cell death after 10 min. Measuring nitrite and nitrosothiols reveals that plasma-treatment leads to an increase of these NO-products in buffer solution and cell culture medium. Using an intracellular fluorescent NO-probe and analysing the nitrosation status of plasma exposed skin cells we can prove that NO indeed reaches and penetrates into these cells. Non-toxic exposure times modulate proliferation in both cell types used, indicating that the gas species, mainly NO, are biological active.

DBD plasma source operated in single-filamentary mode for therapeutic use in dermatology

Our dielectric barrier discharge (DBD) plasma source for bio-medical application comprises a copper electrode covered with ceramic. Objects of high capacitance such as the human body can be used as the opposite electrode. In this study, the DBD source is operated in single-filamentary mode using an aluminium spike as the opposite electrode, to imitate the conditions when the discharge is ignited on a raised point, such as hair, during therapeutic use on the human body. The single-filamentary discharge thus obtained is characterized using optical emission spectroscopy, numerical simulation, voltage–current measurements and microphotography. For characterization of the discharge, averaged plasma parameters such as electron distribution function and electron density are determined. Fluxes of nitric oxide (NO), ozone (O3) and photons reaching the treated surface are simulated. The calculated fluxes are finally compared with corresponding fluxes used in different bio-medical applications.

Characterization of transient discharges under atmospheric-pressure conditions applying nitrogen photoemission and current measurements

The plasma parameters such as electron distribution function and electron density of three atmospheric-pressure transient discharges namely filamentary and homogeneous dielectric barrier discharges in air, and the spark discharge of an argon plasma coagulation (APC) system are determined. A combination of numerical simulation as well as diagnostic methods including current measurement and optical emission spectroscopy (OES) based on nitrogen emissions is used. The applied methods supplement each other and resolve problems, which arise when these methods are used individually. Nitrogen is used as a sensor gas and is admixed in low amount to argon for characterizing the APC discharge. Both direct and stepwise electron-impact excitation of nitrogen emissions are included in the plasma-chemical model applied for characterization of these transient discharges using OES where ambiguity arises in the determination of plasma parameters under specific discharge conditions. It is shown that the measured current solves this problem by providing additional information useful for the determination of discharge-specific plasma parameters.

Space-resolved characterization of high frequency atmospheric-pressure plasma in nitrogen, applying optical emission spectroscopy and numerical simulation

Averaged plasma parameters such as electron distribution function and electron density are determined by characterization of high frequency (2.4 GHz) nitrogen-plasma using both experimental methods, namely optical emission spectroscopy (OES) and microphotography, and numerical simulation. Both direct and stepwise electron-impact excitation of nitrogen emissions are considered. The determination of space-resolved electron distribution function, electron density, rate constant for electron-impact dissociation of nitrogen molecule and the production of nitrogen atoms, applying the same methods, is discussed. Spatial distribution of intensities of neutral nitrogen molecule and nitrogen molecular ion from the microplasma is imaged by a CCD camera. The CCD images are calibrated using the corresponding emissions measured by absolutely-calibrated OES, and are then subjected to inverse Abel transformation to determine space-resolved intensities and other parameters. The space-resolved parameters are compared, respectively, with the averaged parameters, and an agreement between them is established.

Quantitative characterization of a dielectric barrier discharge in air applying non-calibrated spectrometer, current measurement and numerical simulation

A non-calibrated spectrometer is used for quantitative characterization of a dielectric barrier discharge (DBD) in air wherein optical emission spectroscopy (OES) is completed by current measurement and numerical simulation. This diagnostic method is applicable when the cross-sectional area of the active plasma volume and the current density can be determined. The nitrogen emission in the spectral range of 330?406?nm is used for OES diagnostics. The electric field in the active plasma volume is determined by applying the measured spectrum, well-known Franck?Condon factors for nitrogen transitions and numerically simulated electron distribution functions. The measured electric current density is used for the determination of electron density in plasma. Using the determined plasma parameters, the dissociation rates of nitrogen and oxygen in active plasma volume are calculated, which can be used for the simulation of chemical kinetics.

Basics and Biomedical Applications of Dielectric Barrier Discharge (DBD)

Plasmas are partially ionized gases and are described as the “fourth state” of matter. Irving Langmuir coined the word ‘plasma’, in 1928, for the ionized gas in which electrons, ions, and excited particles are suspended similar to the cells suspended in the blood plasma. Naturally-existing plasma includes the sun and the stars, lightening, polar lights, etc. Artificially-produced plasmas are fluorescent lamps, neon signs, plasma displays and monitors, etc. Much more applications of plasma have been made possible in the recent decades. There are several methods for plasma generation. One among them is by applying sufficient electric field in different gas mixtures confined in a low-pressure chamber. Such lowpressure plasmas are suitable for tailoring the surface properties of different materials, for film deposition, for sterilization of non-living matter, etc. However, treatment of pressuresensitive objects and materials is not possible using a low-pressure system. Treatment of living tissues, as in the case of medical treatment, is possible only with plasma devices which operate at atmospheric pressure. Because of high pressure, discharge ignition at atmospheric conditions requires high voltage and can arouse high current density. The gas temperature in active plasma volume increases up to several thousand degrees. By such treatment, the living object is over heated (hyperthermia) and partially evaporated. Such plasma sources are used in surgery as plasma scalpel and blood coagulator (Stoffels, 2007). For gentle treatment of living object at atmospheric pressure conditions, limitation of current flowing through the treated object is necessary. This can be achieved by placing the object slightly away from the active plasma volume as in the case of “indirect” plasma treatment. The other ways are short voltage pulsing (Ayan, 2008 & Walsh, 2008) and using a dielectric barrier (otherwise called ‘insulator’) that drastically reduces electric current through the treated object. Devices using the latter are so-called “dielectric barrier discharges (DBD)” which are useful for “direct” treatment of living object which comes in immediate contact with the plasma.