Sterilization of dental bacteria in a flowing N/sub 2/-O/sub 2/ post discharge reactor: roles of plasma species and of temperature

Abstract

Summary form only given. The effect of a N/sub 2/-O/sub 2/ microwave flowing post discharge on the sterilization of different bacteria has been studied. Optimization of the process was performed varying gas mixture, source power, pressure and substrate temperature. For a better understanding of the sterilization mechanisms in post-discharge environments, we have determined the absolute concentrations of N and O atoms by TALIF coupled to previous results obtained by NO titration technique. We have specified the role of each N and O active species and UV emission, coming from recombination of N and O atoms to produce radiative NO molecules, in the sterilization mechanisms. We have shown that without external heating the holder temperature increased with the oxygen concentration in the post discharge and this increase depended on the holder material. This indicates clearly that oxygen atoms are the main species producing elevation of temperature then enhancing sterilization. We have also pointed out the sterilization action of nitrogen atoms when performing pure N/sub 2/ microwave discharge. Finally, we have observed a bacteria concentration decrease of 6 log at 80/spl deg/C after 20 min exposure and of 12 log at 120/spl deg/C after 5 min. exposure, with a N/sub 2/-5%O/sub 2/ gas mixture at a pressure of 5 Torr, a microwave power of 100 watts in a quartz tube of 5 mm internal diameter and a flow rate of 1 slm.