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Summary form only given. It has been demonstrated recently that direct treatment of relatively smooth surfaces by non-thermal dielectric barrier discharge (DBD) in air is highly effective in killing bacteria and fungi. The key aspect of the direct treatment was shown to be contact with electrical charges. These results hold significant promise for medical applications of direct DBD such as sterilization of wound surfaces. However, a typical DBD in air can be highly non-uniform, particularly on topographically non-uniform surfaces such as most of the living tissues. As a result, it is not clear that pathogens can be destroyed as effectively on the recessed areas between the ridges of real tissue by the conventional DBD in air. In this study authors have investigated effectiveness of a DBD excited by nanosecond rise and fall time voltage pulses in killing bacteria covering topographically non-uniform surfaces. Sterilization experiments were conducted on the E. coli covered agar surface acting as one of the DBD electrodes. The nanosecond-pulsed DBD (ns-DBD) was tested on non-uniform surfaces and produced uniform plasma independent of the surface topography. Sterilization effectiveness of ns-DBD also has been compared with that of a conventional DBD, i.e. microsecond-pulsed DBD (ms- DBD). Experiments reveal that the ns-DBD sterilizes a larger surface area than the ms-DBD does for the same duration and power. Moreover, experiments on non-uniform surfaces showed that the ns-DBD can penetrate into the recessed areas and sterilizes completely whereas the ms-DBD fails to do so. In summary, ns-DBD with short rise time and high overvoltage is insensitive to the morphological non-uniformities of the surface. Thus DBDs with nanosecond rise times are potentially more convenient for in vivo and hospital sterilization. Although several investigators did report uniform DBD systems, to the authors' knowledge the uniform discharge reported here is the only one to have been demonstra- ed at atmospheric pressure in open moist air over topographically non-uniform surfaces.
Date of Conference: 1-5 June 2009