Sterilization characteristics of narrow tubing by nitrogen oxides generated in atmospheric pressure air plasma

The sterilization characteristics of active species generated by an atmospheric dielectric barrier discharge plasma using air and oxygen at the inner surface of silicone tubing were investigated. A dielectric barrier discharge torch plasma device was installed at one end of the tube and generated long-lived active species that flowed into the tube. A strip-type biological indicator with a 105-cell bacterial spore was placed at the opposite end of the 60 cm tube. Sterilization was completed within 30 min by active particles generated from the air plasma. The main factors contributing to the sterilization by air plasma were HNO3 and N2O5. When organic materials (keratin, aspartic acid, and dipicolinic acid) reflecting components of the bacterial spore, were treated by the sterilization procedure there was little effect on dipicolinic acid. Keratin was oxidized by ozone and NOx generated from the oxygen and air plasmas, respectively. Aspartic acid underwent little change in composition from ozone generated from the oxygen plasma, whereas nitro (NO2), nitroso (NO), and aldehyde (CHO) groups were formed from ozone and NOx generated from the air plasma.