Roland Gesche

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.

Non-thermal atmospheric pressure HF plasma source: generation of nitric oxide and ozone for bio-medical applications

A new miniature high-frequency (HF) plasma source intended for bio-medical applications is studied using nitrogen/oxygen mixture at atmospheric pressure. This plasma source can be used as an element of a plasma source array for applications in dermatology and surgery. Nitric oxide and ozone which are produced in this plasma source are well-known agents for proliferation of the cells, inhalation therapy for newborn infants, disinfection of wounds and blood ozonation.Using optical emission spectroscopy, microphotography and numerical simulation, the gas temperature in the active plasma region and plasma parameters (electron density and electron distribution function) are determined for varied nitrogen/oxygen flows. The influence of the gas flows on the plasma conditions is studied. Ozone and nitric oxide concentrations in the effluent of the plasma source are measured using absorption spectroscopy and electro-chemical NO-detector at variable gas flows. Correlations between plasma parameters and concentrations of the particles in the effluent of the plasma source are discussed. By varying the gas flows, the HF plasma source can be optimized for nitric oxide or ozone production. Maximum concentrations of 2750 ppm and 400 ppm of NO and O3, correspondingly, are generated.

Electric probe investigations of microwave generated, atmospheric pressure, plasma jets

We examine the applicability of the Langmuir-type of characterization for atmospheric pressure plasma jets generated in a millimeter-size cavity microwave resonator at 2.45 GHz. Wide range I-V characteristics of helium, argon, nitrogen, air and oxygen are presented for different gas fluxes, distances probe-resonator, and microwave powers. A detailed analysis is performed for the fine variation in the current around the floating potential. A simplified theory specially developed for this case is presented, considering the ionic and electronic saturation currents and the floating potential. Based on this theory, we conclude that, while the charge carrier density depends on gas flow, distance to plasma source, and microwave absorbed power, the electron temperature is quite independent of these parameters. The resulting plasma parameters for helium, argon, and nitrogen are presented.

Integrated Microwave Atmospheric Plasma Source (IMAPlaS): thermal and spectroscopic properties and antimicrobial effect on B. atrophaeus spores

The Integrated Microwave Atmospheric Plasma Source (IMAPlaS) operating with a microwave resonator at 2.45 GHz driven by a solid-state transistor oscillator generates a core plasma of high temperature (T > 1000 K), therefore producing reactive species such as NO very effectively. The effluent of the plasma source is much colder, which enables direct treatment of thermolabile materials or even living tissue. In this study the source was operated with argon, helium and nitrogen with gas flow rates between 0.3 and 1.0 slm. Depending on working gas and distance, axial gas temperatures between 30 and 250 °C were determined in front of the nozzle. Reactive species were identified by emission spectroscopy in the spectral range from vacuum ultraviolet to near infrared. The irradiance in the ultraviolet range was also measured. Using B. atrophaeus spores to test antimicrobial efficiency, we determined log10-reduction rates of up to a factor of 4.

Low-Power Microwave Plasma Conductivity

Plasma conductivity is of general interest for both fundamental research and specific applications. For this purpose, plasma equivalent impedance and complex conductivity are measured at 2.2 GHz, at pressures between 1 and 103 mbar, as a function of microwave power in a slot-type resonator, predominantly capacitively coupled to plasma. The plasma impedance is self-adjusting, maintaining a quasi-constant microwave amplitude. The sign of the imaginary part of the impedance (or conductivity) depends on pressure and, consequently, on electron density. The reactive part becomes significant if the Debye length is comparable with the size of the resonator and the plasma frequency is close to the microwave driving frequency.

Global models for the microwave driven double icp plasma jet

Summary form only given. For many technical applications, microwave driven plasma jets are possible alternatives to conventional RF plasma sources. They are of uncomplicated construction, and have the advantages of small size and large electrical efficiency.

Langmuir-type of investigations of atmospheric pressure plasma jets

The new generation of microplasma sources, generating plasma jets of few millimeter size at atmospheric pressure, requires specific methods of characterization.

Ignition delay of microplasmas at atmospheric pressure

Micarowave field breakdown conditions in gases are important whenever using plasma in pulsed mode. The plasma properties during the steady state regime are different from those during the ignition time.

Microwave excitation of metal halide plasma lamps

High pressure metal halide plasma (HID) lamps as compact light sources are characterized by high efficiency, excellent color rendering and long lifetime. Usually the lifetime is mainly influenced by electrode erosion leading to wall blackening and a reduction of the luminous flux. Therefore it is of actual research interest to have an electrodeless power input into HID lamps. More then ten years ago there was a high power electrodeless sulfur lamp with a microwave excitation commercially available1. New trends with lower power HID units below 50 W including research on electrodeless HID lamps could expand the field of application and break into new markets. This work discusses the high frequency power input and the plasma behavior in high pressure lamps2,3. Therefore several lamp geometries and lamp fillings were tested. The lamps were made of quartz and ceramics containing Ar as an ignition gas and several metal halides as light emitting substances. The lamps were ignited by an external high voltage pulse and operated in a special resonator configuration at frequencies around 2.45 GHz. The main energy input by inductive coupling was varied between 5 and 30 W. The power supply was built on a semiconductor basis. Input power, spectral distribution in the visible spectral range and vessel temperature were observed by a vector network analyzer, a fiber spectrometer and an infrared camera respectively. To enhance the vapor pressure of the additives, the lamps were also operated in a vacuum chamber. Variations in the filling, the input power and the wall temperature lead to changes in the spectral output, color temperature, color rendering and to changes in the coupling with the circuit. Further experiments are planed to study the influence of other resonator configurations and lamp shapes.

A Novel Self-Pinching Gate Biasing Scheme for Safe Operation and Characterization of GaN HEMTs

This letter presents a novel gate bias configuration for GaN HEMTs that ensures a safe operation of this kind of device by protecting the gate from forward turn-on. The bias circuit includes a simple series diode in the DC path that blocks any positive current from the gate, in other words it restricts the gate diode of the device to operate in forward bias. The new bias circuit ensures a safe operating condition of FET/HEMT transistors during forward turn-on while not hampering or degrading performance under normal operating condition.