Sterilization effect of nitrogen oxide radicals generated by microwave plasma using air

• A sterilization experiment using a microwave plasma at 60 °C or less was conducted.
• The number of bacilli was 1/10th the original number in about 10 min.
• The sterilization factor is the nitrogen oxide radicals made by microwave plasma.

Plasma sterilization has attracted attention as a safe and low cost sterilization method compared to conventional sterilization methods such as EOG (ethylene oxide gas) sterilization and high-pressure steam sterilization. In this research, a plasma is generated by irradiating air with microwaves. Sterilization is caused by 0-radicals and NO-radicals. In order to carry out sterilization efficiently, optimal setting of equipment conditions is required. The pressure required for optimal conditions of the equipment, the microwave output, and the equipment used have been examined. A biological indicator (BI), Geobacillus stearothermophilus (ATCC7953), was used. It was found that sterilization was successful when the pressure in the vacuum chamber for microwave output of 280 W was 60 Pa.