Remote Plasma Treatment of Bacteria using Non-Equilibrium Atmospheric Pressure Air Dielectric Barrier Discharge (DBD)

Summary form only given. Atmospheric pressure air dielectric barrier discharge (DBD) was used for remote treatment of bacteria. The DBD system consists of two water-cooled Al electrodes (75 mm in diameter), attached to dielectric (Al₂O₃) plates 115 mm times 115 mm times 1 mm with a thermal conducting paste. Operating frequency was fixed to 3.4 kHz, and the interelectrode gap was set to 3.6 mm. The biological sample was located in a separate compartment 5 cm away from the plasma region, and the air activated by the discharge was passing through that chamber at different flow rates. At this long distance from the discharge and at high pressure no charge particles could reach the bacterial sample. The temperature of the sample was kept below 320 K. At these operating conditions, the major reason for the fast bacterial deactivation is the generation of chemically active long-lived species (O₃, NO_x, etc.). We found that the killing rate of bacteria in this experimental setup is strongly dependent on the air flow rate: at low gas flow rate (1 l/min) the killing was not pronounced, while at higher flow rate (10 l/min) reduction of at least 5 orders of magnitude was observed after 180 sec. of remote plasma treatment. Furthermore, changes in the metabolic behavior of bacteria due to exposure to radicals generated by plasma were studied, using Biolog´s GN2 plate, a 96-well microtiter plate containing 95 different carbon substrates, the composition of which is dominated by amino acids, carbohydrates, and carboxylic acids. Comparison between the sole-carbon-source-utilization profiles of the original bacteria (controls) and profiles of bacteria that survived and grew following exposure to the radicals will be presented