Development of catalyst materials being effective for microwave sterilization

Recently, airborne virus infections have emerged as some of the most challenging medical problems. To prevent the threat of infection, the processes of sterilization have been studied widely. Microwave sterilization has many advantages in comparison with conventional methods. It is able to raise the temperature of a material in a short time and selectively heat the material. This results in the reduction of usage and the rapid completion of sterilization. We developed a novel microwave sterilization system that can raise the temperature in quite a short time using a lower microwave power (100 W). Filters made with Kao wool (Al2O3) were coated with TiO2 (anatase) by sol-gel method and used to trap microorganisms. In addition, these filters were coated with Pt or Ag by impregnated method. We also prepared a Tyranno-fiber textile filter and a honeycomb SiC filter. Two microorganisms, Bacillus subtilis ATCC 9372 and Bacillus stearothermophilus ATCC 7953, were used in this experiment, where either microorganism was loaded onto a filter. After irradiation, filters loaded with B. subtilis and B. stearothermophilus were incubated for 48 h in a TSB medium (Bacto™ Tryptic Soy Broth, Becton, Dickinson and company sparks, MD) at 37 and 56 °C, respectively. B. subtilis and B. stearothermophilus loaded on to Ag-impregnated filters were sterilized in 30 and 15 s, respectively. The Tyranno-fiber textile filter and the honeycomb SiC also filter showed effective microwave sterilization. These results showed that this system could sterilize B. subtilis and B. stearothermophilus in quite a short time and that microwave absorbable materials are effective as microwave sterilization filters.