Reactive Oxygen Species in a Non-thermal Plasma Microjet and Water System: Generation, Conversion, and Contributions to Bacteria Inactivation-An Analysis by Electron Spin Resonance Spectroscopy

Hydroxyl radical ((OH)-O-center dot) and singlet oxygen (O-1(2)) were detected by electron spin resonance (ESR) spectroscopy in a direct current He/O2 (2%) non-thermal plasma microjet-water system. O-center dot(2)- is shown to be the precursor of (OH)-O-center dot. The concentrations of O-1(2) and (OH)-O-center dot are evaluated to be around 6 X 10(-4) and 1.2 X 10(-5)M, respectively. The survival rates of S. aureus exposed to plasma for 20s in 1ml H2O, SOD (100 U, for scavenging O-center dot(2)-, D-Man (0.15 M, for scavenging (OH)-O-center dot), and L-His (0.15 M, for scavenging (OH)-O-center dot and O-1(2)) solutions were 0.7, 1.6, 13.4, and 40.9%, respectively, indicating that O-1(2) contributes the most to the inactivation.