The Effect of Gap Distance between a Pin and Water Surface on the Inactivation of Escherichia coli Using a Pin-to-Water Plasma

Atmospheric plasmas have been applied for the inactivation of microorganisms. Industrials demand to investigate the relation of the key reactive species induced by plasmas and the operating parameters including boundary conditions in order to control plasma treatment processes. In this study, we investigated the effect of gap distance between a pin-electrode and water surface on inactivation efficacy. When the gap distance decreased from 5 mm to 1 mm, the reduction of Escherichia coli (E. coli) was increased to more than 4 log CFU/mL. The reactive oxygen species measured optically and spectrophotometrically were influenced by gap distance. The results from electron spin resonance (ESR) analysis showed that the pin-to-water plasma generated hydroxyl radical (OH center dot) and singlet oxygen (O-1(2)) in the water and superoxide radical (O-2(-)center dot) served as a precursor of OH center dot. The inactivation of E. coli was significantly alleviated by sodium azide (O-1(2) scavenger), indicating that O-1(2) contributes the most to bacterial inactivation. These findings provide a potentially effective strategy for bacterial inactivation using a pin-to-water plasma.

Automated summary

This study investigated the effect of gap distance between a pin-electrode and water surface on the inactivation efficacy of Escherichia coli (E. coli). The results showed that as the gap distance decreased, the reduction of E. coli increased, and the reactive oxygen species were influenced by the gap distance. Electron spin resonance analysis revealed that the pin-to-water plasma generated hydroxyl radical and singlet oxygen, with superoxide radical serving as a precursor of the hydroxyl radical. Importantly, singlet oxygen (O-1(2)) contributed the most to bacterial inactivation.