Disinfection of {\it S.~mutans} Bacteria Using a Plasma Needle at Atmospheric Pressure

The plasma needle device produces a millimeter-size low-power glow discharge at atmospheric-pressure. It is intended for dental or medical applications. Radio-frequency high voltage is applied to a single needle electrode located inside a concentric gas-flow nozzle. A low-speed helium plasma jet flows out of the nozzle and mixes with ambient air. The jet is impinges on a surface that is to be treated, which in our test was a suspension of {\it S.~mutans} bacteria that was plated onto the surface of agar nutrient in a Petri dish. {\it S.~mutans} is the most important microorganism for causing dental caries. Imaging the sample after plasma treatment and incubation reveal the conditions where bacteria are killed, and the size of the treated spot.