2151-805X/11/$35.00 © 2011 by Begell House, Inc. 179 Plasma Medicine, 1(3–4): 179–189 (2011) Design of Experiment-based Testing of Air, Charged Ions, and Hydrogen Peroxide in a Direct Current Steady-State Plasma Sterilizer Arun Balasundaram, 1 Igor Alexeff, 2 * Rapinder S Sawhney 1 1 Department of Industrial and Information Engineering and 2 Department of Electrical Engineering, University of Tennessee, Knoxville *Address all correspondence to: Igor Alexeff, Department of Electrical Engineering, University of Tennessee, 315 Ferris Hall, 1508 Middle Drive, Knoxville, TN 37996-2100; alexeff@utk.edu. ABSTRACT: Three primary factors, hydrogen peroxide, charged ions, and air (oxygen), were evaluated in the kill rate of Escherichia coli bacteria. The results were evaluated by analysis of variance and regression analysis. Air and charged ions are found to be extremely effective. These two factors in combination strongly enhance each other. The hydrogen peroxide did not enhance the kill rate. KEY WORDS: plasma sterilizer; air, charged ions, hydrogen peroxide; DC barrier discharge, ANOVA test, E. coli I. INTRODUCTION Our resistive barrier discharge (RBD) has been demonstrated to be successful on Escherichia coli, Pseudomonas fuorescens (5RL), spores, and bacteriophages. It has been tested successfully in sterilizing pagers contaminated with methicillin-resistant Staphylococcus aureus at the St. Jude Research Hospital in Memphis, Tennessee. Here, we evaluate 3 primary factors in the atmospheric pressure RBD: hydrogen peroxide, charged ions, and air (oxygen). The experiment used analysis of variance (ANOVA) and regression analysis. The tests used 144 Petri dishes and the E. coli bacteria. Hydrogen peroxide was used as a replacement for the water conductor on the RBD electrode. The charged ions were removed by a double charged wire mesh between the discharge and the Petri dish. The air was displaced by a slow fow of nitrogen into the experimental area. The basic conclusions are that air and charged ions both are extremely effective in killing bacteria. In addition, air and charged ions together strongly enhance each other. In our experiments, hydrogen peroxide did not enhance the kill rate. The effects of electric felds and ultraviolet light were not tested. Electric felds are excluded from the exposure area by the design of the apparatus. Ultraviolet light from our discharge was measured previously and was found to be very low compared with ultraviolet light from a mercury discharge tube. Interest and research efforts in the feld of atmospheric pressure nonthermal plasma have grown signifcantly during the past decade. The need for robust sterilization tech- niques that preserve surface integrity in the feld of biological decontamination has only helped the cause. 1–4 Atmospheric pressure nonthermal plasma discharges are known to