Sterilization of bacteria at low discharge voltage by using microplasma

In this paper, Gram-negative Escherichia coli JCM20135 and Gram-positive Bacillus subtilis JCB20036 were used as the target to be sterilized. The experiments were performed with air and nitrogen as the carrier gas, in order to investigate the influence of different radical species in the microplasma, on the bacteria cultures. Two stainless steels electrodes covered with dielectric barrier materials were faced together. By applying a high frequency AC voltage (about 25 kHz), microplasma was generated between the electrodes. Sterilization by microplasma was confirmed at a relatively low discharge voltage of 1.0 kV when the carrier gas was both air and nitrogen. The sterilization rate by air plasma was better than the results by nitrogen plasma due to the combination effect of ozone, high electric field, UV radiation and other radicals. The sterilization rate of E. coli was better than the results for B. subtilis due to the characteristics of the cell wall, which is different in thickness and chemical composition.