DC operated atmospheric pressure air plasma jet for biomedical applications

We have previously presented a gas discharge assembly based on a microhollow cathode geometry which can be operated with a dc current at atmospheric pressure with ambient air1. By flowing air through the discharge channel at a rate of about 7 Ltr/min a 10-20-mm long plume is observed. The temperature in this expelled afterglow plasma reaches values that are close to room temperature at a distance of 5 mm from the discharge origin. Emission spectra show that atomic oxygen, hydroxyl ions and various nitrogen compounds are generated in the discharge and are driven out with the gas flow. The most prominent secondary discharge product, ozone, is detected in high concentrations. The low heavy-particle temperature allows us to use this exhaust stream on biological samples and tissues without thermal damage. The high levels of reactive species suggest an effective treatment for pathological skin conditions caused, in particular, by infectious agents. In the first experiments, we have successfully tested the efficacy of this afterglow plasma on Candida kefyr (a yeast), E.coli (bacteria), and a matching E.coli strain-specific virus, 0X174 (a bacteriophage). All pathogens investigated responded well to the treatment. In the yeast case, complete eradication of the organism in the treated area could be achieved with an exposure of 90 seconds at a distance of 5 mm. A 10-fold increase of exposure, to 900 seconds caused no observable damage to murine integument. The quantification of the response, and studies of possible mechanisms are underway.