title: The dependence of the sporicidal effects on the power and pressure of RF-generated plasma processes.
abstract: The sporicidal effect of 20 different radio-frequency plasma processes produced by combining five different gas mixtures [O(2), Ar/H(2) (50/50%), Ar/H(2) (5/95%), O(2)/H(2) (50/50%), O(2)/H(2) (95/5%)] with four power/pressure settings were tested. Sporicidal effects of oxygen-containing plasmas were dependent on power at low pressure settings but not at high pressure settings. In the absence of oxygen no power dependency was observed at either high or low pressure settings. Survivor curves obtained with the use of nonoxygen plasmas typically had a tailing tendency. Only a mixture-optimized Ar/H(2) (15/85%) plasma process was not encumbered by tailing, and produced a decimal reduction time (D value) below 2 min for Bacillus stearothermophilus spores. Scanning electron microscopy showed that a CF(4)/O(2) plasma did more damage to the substrate than the 15/85% Ar/H(2) plasma. The present results indicate that UV irradiation inactivation is swift and power and pressure independent. Additionally, it is produced at low energy. However, it is not complete. Inactivation through etching is highly power and pressure dependent; finally, inactivation by photodesorption is moderately power and pressure dependent. A sterilization process relying on this mechanism is very advantageous because it combines a highly sporicidal effect with low substrate damage.
authors.affiliation: The National Centre for Hospital Hygiene (CAS), Statens Serum Institut, Copenhagen S, Denmark. ksl@ssi.dk
authors.forename: Klaus S
authors.initials: KS
authors.lastname: Lassen
authors.forename: Bolette
authors.initials: B
authors.lastname: Nordby
authors.forename: Reinar
authors.initials: R
authors.lastname: Grün
mesh_terms: D000704:Analysis of Variance; D001128:Argon; D004566:Electrodes; D004866:Equipment Contamination / Q000517:prevention & control; D004867:Equipment Design; D004864:Equipment and Supplies / Q000382:microbiology; D005740:Gases; D001411:Geobacillus stearothermophilus / Q000528:radiation effects; D006859:Hydrogen; D008027:Light; D008855:Microscopy, Electron, Scanning; D010100:Oxygen / Q000378:metabolism; D011312:Pressure; D011846:Radio Waves; D013171:Spores, Bacterial / Q000528:radiation effects*; D013242:Sterilization; D013997:Time Factors; D014466:Ultraviolet Rays
chemical_list: D005740:Gases; D001128:Argon; D006859:Hydrogen; D010100:Oxygen