Inactivation of Staphylococcus aureus in Water by a Cold, He/O2 Atmospheric Pressure Plasma Microjet

A direct-current, atmospheric pressure, cold plasma microjet (PMJ) sustained in a quasi-steady gas cavity in liquid was used to inactivate Staphylococcus aureus suspended in distilled water. While helium gas (with 2% O-2 as additive) was used as working gas, an effective inactivation(>99%) was achieved in 6 min. The inactivation of bacteria was further verified by surface morphology examination and LIVE/DEAD Baclight bacterial viability test (fluorescence microscopy). The overall pH and temperature of the liquid were monitored during the plasma treatment and were found to be below the critical values for the survival of S. aureus. Hydroxyl radical ((OH)-O-center dot) was detected via electron spin resonance (ESR) spectroscopy, and alongside other intermediate reactive species, is attributed to the effective inactivation of S. aureus. End-on optical emission spectroscopy show strong atomic oxygen emission both in air and in water.