Germicidal efficiency and mechanisms of escherichia coli by remote oxygen plasma

Double Langmuir electron probes and electron spin resonance (ESR) were used to measure the distribution of electrons, ions and free radicals in remote oxygen plasma. The germicidal effect (GE) of Escherichia coli on the surface of medical polytetrefluoroethylene (PTFE) film by remote oxygen plasma was investigated, and then, the quantity of protein leakage and the production of lipid peroxide in bacterial suspension as well as DNA agarose electrophoresis were measured after sterilization to analyse the inactivation mechanisms. The results show that in remote oxygen plasma, the concentrations of electrons and ions decrease rapidly with the increasing distance from the center of induction coil, which approach to zero at 30 cm, whereas the concentration of free radicals reduces slowly, namely, decrease 30% within 40 cm. GE reaches 3.42 in discharge zone (0 cm) and exceeds 3.32 within 40 cm when plasma treatment parameters are set as plasma RF power at 100 W, treatment time at 60 s and oxygen flux at 40 cm³/min. Fast etching action on cell membrane by electrons, ions and attacking polyunsaturation fatty acid (PUFA) in cell membrane by free radicals are the primary reasons of oxygen plasma sterilization in discharge and remote zone, respectively. The GE of UV radiation in remote oxygen plasma gets feeble.