DC powered atmospheric pressure micro-plasmajet for biomedical applications

Summary form only given. Nonthermal (cold) plasmas operated in air at atmospheric pressure offer an appealing method for the processing and decontamination of surfaces. Most existing devices are operated with radiofrequency high voltages. Microhollow cathode discharges (MHCDs), on the other hand, allow us to generate a direct current driven plasma jet in atmospheric pressure gases, including air. The discharge is sustained by a voltage of only several hundred volts applied to two plane metal electrodes which are separated by a dielectric insulator. The plasma is confined in a cylindrical channel drilled through all layers. With a thickness of the dielectric of 0.25 mm and a diameter of the channel of less than 1 mm a stable glow discharge can be sustained. By flowing air or nitrogen through the channel into atmospheric pressure air, a well-defined plasma (afterglow) jet is generated with a typical, visible length of 10-20 mm. The gas temperature of air and nitrogen plasmas inside the channel was measured by means of emission spectroscopy using the 0-0 band within the second positive system of nitrogen. Increasing the flow rate from 0 to 200 ml/min resulted in a decrease in gas temperature from 2000 K to 800 K in the channel. The lower temperature allows us to replace high temperature ceramics and metals, such as alumina and molybdenum, respectively, with less expensive and easier machinable materials. The turbulent gas flow effectively cools the plasma jet down further to temperatures close to room temperature at a distance of 5 mm from the nozzle. This allows using this micro-plasma jet for treatment of heat sensitive materials and surfaces. E.g., the wettability of polypropylene (melting point 170degC) was increased by 70% when treated with the plasma jet. Other applications include the gentle cleaning and decontamination of organic materials. Studies on the treatment of fungal, viral, and bacterial skin diseases with the plasma jet are underway