Cold Atmospheric Pressure Air Plasma Microjet for Medical Applications

Summary form only given. In recent years, several devices, able to generate a cold plasma-plume at atmospheric pressure in air, have been demonstrated. The plasma is generally operated with radiofrequency high voltages or pulsed high voltages applied with repetition rates in the radiofrequency range. In addition, stable operation requires running the discharge in a noble gas such as argon or helium. Ambient air is incorporated into the operating gas, accounting for only a few percent of the mixture. An alternative solution is offered by micro-discharge geometries. We have recently developed a dc-voltage driven micro-discharge that overcomes this limitation and can be operated in pure air at atmospheric pressure or higher. The discharge is sustained by only several hundred volts applied between two electrodes in a microhollow cathode geometry. By flowing the operating gas (air or nitrogen) through the discharge into atmospheric pressure air, a well-defined plasma (afterglow) jet is generated with a typical, visible length of 10- 20 mm. Reactive species such as hydroxyl-molecules, atomic oxygen and ozone are expelled with the gas flow and can react with materials at a distance of up to a few centimeters. Combined with the low heavy particle temperature, the afterglow stream generated is particularly suitable for the treatment of heat sensitive materials, e.g. plastics, or tissues such as skin. First experiments on the efficacy of the plasma in biomedical applications were done on Candida. The related yeast infection is generally treated with antibiotics. However, increased resistance to antibiotics is considered to be a leading factor in the increased rate of infections. In comparison: a single treatment of 90 seconds with the plasma microjet can remove the fungus completely in a 1 cm² area.