Atmospheric Air Plasma Streamers Deliver Nanosecond Pulses for Focused Electroporation

Background: For electrotherapies that involve electrodes and high-intensity electric fields, such as in tissue ablation, we report a method of pulse delivery that can focus the electric field away from the electrodes, as demonstrated in vitro.Materials and Methods: To electroporate cells in a monolayer seeded in a 35 mm culture dish, two atmospheric-pressure plasma channels generated by two thin, copper foil electrodes above the surface of the solution provided the current and established the electric field.Results: Depending on the pulse duration, the plasma channels were observed as corona (100 ns), streamer (300 ns), and mixture of streamer and arc (1 mu s). With the Yo-pro-1 and propidium iodine uptakes as electroporation markers, the corona plasma did not cause observable electroporation. The streamer and arc mixed plasma allowed a large area of monolayer cells to be electroporated. Only the streamer channels allowed the focused electroporation of the cells at the center area on the culture dish, while the areas directly under the electrodes showed weak or no response. It is a desired effect that could not be achieved by electrodes directly touching cells or cell solution.Conclusion: The focused poration was most likely caused by nanosecond pulsed electric fields, not by plasma chemistry.