An oxygen-radical generator for the decontamination of biological warfare agents

An arc-seed microwave plasma torch, which is operated at a 60 Hz periodic mode (with about 40 % duty cycle), runs stably at low airflow rate, and produces an abundance of reactive atomic oxygen in its plasma effluent, is applied to study the effects of atomic oxygen on bacterial spores. Bacillus cereus is chosen as the biological agent. Drops of bacterial-spore solution are inoculated onto glass/paper slide-coupons and desiccated into dry samples as well as inoculated onto the wells of 96-well microplates as wet samples. Decontamination experiments are performed with the airflow rate of 0.393 l/s, corresponding to a maximum concentration of atomic oxygen produced by the torch. The experimental results show that all spores in dry samples on glass slide-coupons, placed at distances of 3, 4, and 5 cm away from the nozzle of the torch, are killed in less than 8, 12, and 16 seconds, respectively. The torch also kills spores in the paper coupon placed inside an envelope without damaging the envelope. At an exposure distance of 4 cm, the measured kill time (i.e., 10-fold reduction time) is about 9 seconds. The experiments further show that the plasma effluent can penetrate into water to kill B. cereus spores. The kill times are about 10, 24, and 31 seconds at exposure distances of 3, 4, and 5 cm, respectively. Morphological studies were performed via scanning electron and atomic force microscopes, which took two and three-dimensional images of untreated and exposed but still viable spores in wet samples to record the changes in their morphological structures and shapes caused by the plasma effluent. The loss of appendages and exosporium in the structure as well as squashed/flattened cell shapes were observed.