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 this talk, a demonstration is reported showing that the plasma needle kills Streptococcus mutans(S. mutans) bacteria under conditions that are attractive for clinical applications in dentistry. 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. Images of the sample, taken after both plasma treatment and incubation, reveal that S. mutans was killed uniformly within a circle of diameter 5 mm. This demonstrates that plasma-needle treatment can deliver a desirable site-specific disinfection. We also found other operating conditions where bacteria were killed in a ring-shaped region. While this would be undesirable for clinical treatment, it offers an opportunity to gain an understanding plasma transport processes. Optical imaging and spectroscopy diagnostics of the plasma needle glow were performed. The ring-shaped killing pattern is explained by the spatial distribution of energetic electrons, as revealed by Abel-inverted images of the glow. The presence of radicals OH and O, which are known to be bactericidal was verified using OES