Focusing mechanism for an increased H2O2 plasma sterilization efficiency

Abstract

A modified dc glow discharge facility operating at low H₂O₂ pressure was used in the sterilization of samples contaminated with B. subtilis. Parallel electrodes of stainless steel having diameters 12.0 cm and separated by 1.0 cm are encapsulated by a 0.7 mm thick copper sheet formed into a cylinder of 7.0 cm height and 15.0 cm diameter. The glow is obtained at initial gas filling pressures 0.5−1.0 Torr, discharge conditions 8.0 mA current and 400.0 V potential. The copper shield biased at −100 V showed an electric field directing the negative particle flux from anode to cathode, quenching it towards the axial zone of the discharge where the sample is located. The resulting sterilization efficacy increased by 46%; the decimal reduction value obtained in 2.5 minutes and sample temperature measured at 38°C. Optical emission spectra revealed the presence of the OH free radical at 245 nm and dominated by peroxides O₂⁻ at 275 nm, 300 nm, 345 nm, and 346 nm UV radiations between 240 nm and 280 nm are germicidal.