Disinfection of S. Mutans Bacteria Using a Plasma Needle at Atmospheric Pressure

Summary form only given. The "plasma needle" device produces a small-diameter low-power atmospheric-pressure glow discharge. 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. The nozzle has a diameter of a few millimeters, and the plasma that flows out of the nozzle has a comparable diameter. The nozzle is placed a few millimeters from the surface that is to be treated, and the plasma jet is directed onto that surface. When desired, the plasma needle can be operated at a power so low that the glow is barely visible to the unaided eye. Using small-diameter plasma allows site-specific disinfection of spots with a diameter of a few millimeters. In the test, the plasma was applied to a suspension of S. mutans that was plated onto the surface of agar nutrient in a Petri dish. S. mutans is the most important microorganism for causing dental caries. The sample is imaged after plasma treatment and incubation. These tests reveal the conditions where S. mutans are killed, and the size of the treated spot. We investigate the role of bacterial concentration in the sample, and evaporation during treatment. As in our previous experiments, we also investigate the role of gas flow, treatment time, RF voltage, and needle-to-sample separation.