Inactivation of bacteria by a mixed argon and oxygen micro-plasma as a function of exposure time

Purpose: A radio-frequency dielectric barrier discharge (DBD) was applied as a micro-plasma device for the inactivation of bacteria, e.g., Escherichia coli. Materials and methods: The cultured bacteria were placed on a polydimethyl siloxane (PDMS) film and placed inside the DBD cavity. The bacteria were exposed to micro-plasmas of varying oxygen/argon ratios for different exposure times. The survival of the bacteria was measured by determining bacterial growth using optical methods. Results: The excited oxygen species increased with the increase in the oxygen to argon ratio as measured by optical emission spectroscopy (OES), but the increase of excited oxygen species in argon micro-plasma did not enhance the inactivation of bacteria. In contrast, increases in the time the bacteria were exposed to the micro-plasma were of importance. The results show that a continuous plasma flow containing energetic and reactive species may result in electro-physical interactions with bacteria exposed to the plasma leading to their inactivation. Conclusion: For currently-employed DBD device, addition of 0.5% oxygen to the argon micro-plasma for an exposure time of 30 sec was optimum for the inactivation of E. coli.