Study on sterilization effect of different forms of atmospheric pressure plasma jet

Atmospheric pressure plasma jet (APPJ) has a significant effect on the inactivation of pathogenic microorganisms such as bacteria, virus and fungus. However, sterilization effect of APPJ is restricted by many factors: forms of the power supply (pulse, AC, DC, etc.), parameters of the voltage (amplitude, frequency), time and distance of processing, and the parameters of working gas. In this paper, the system consisting of the pulse power supply and the plasma generation device which uses coaxial cylinder tube, are developed by our research team independently. The system can generate plasma jets of low temperature under atmospheric pressure, using helium as working gas. In the experiment, Escherichia coli, which is typical and common in our environment, was used as the processing object to analyze the sterilization effect of APPJ under different power supply parameters, gas flow rate and processing time. In this paper the composition of plasma jet was analyzed by testing infrared spectra of it and the structure of bacteria was observed by scanning electron microscope (SEM) to study the principle of sterilization. The experimental results show that the active ingredients in APPJ will directly act on bacteria, making the bacterial structure destroyed, cell components lost completely and finally the bacteria inactivated; or the cell fragmentation will occur under the electric field, leading to the thorough loss of bacterial morphology. With the increase of the voltage amplitude or the gas velocity, the sterilization ratio of Escherichia coli increases continuously. Also lengthening the processing time is an effective measure to enhance the sterilization ratio of APPJ. When the processing time exceeds 1 minute, sterilization ratios under different parameters of power supply and gas flow rate can reach 90% or more. The sterilization effect of plasma jet can be obviously seen. Compared to traditional methods such as thermal, chemical and radiate sterilization, APPJ sterilization is more effective, cleaner and free from contamination.