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