Previous studies show that nitrogen gas plasma generated by a fast-pulsed power supply using a static induction thyristor has both virucidal and bactericidal effects. In this study, nitrogen gas plasma was further evaluated for its potential effects on prions, which are well known to be the most resistant pathogen to both chemical and physical inactivation. Aliquots (10 μL) of mouse brain homogenate infected with Chandler scrapie prion were spotted onto cover glasses and subjected to nitrogen gas plasma. Treated samples were recovered and subjected to further analyses. Control prion samples were prepared in exactly the same way but without plasma treatment. Protein misfolding cyclic amplification (PMCA) showed that nitrogen gas plasma treatment at 1.5 kilo pulse per second for 15 or 30 min caused a reduction in the in vitro propagation level of PrPres (proteinase K-resistant prion protein), which was used as an index of abnormal prion protein (PrP^Sc). Moreover, mice injected with prion treated with plasma for 30 min showed longer survival than mice injected with control prion, indicating that nitrogen gas plasma treatment decreased prion infectivity. Altogether, these results suggest that nitrogen gas plasma treatment can inactivate scrapie prions by decreasing the propagation activity and infectivity of PrP^Sc.

Experiments reported here were conducted using atmospheric nitrogen gas remote plasma with a pulsed power source. The sterilization efficiency, major sterilization factors and most appropriate sterilization conditions were determined. By varying several factors such as hotplate temperature, relative humidity, water vapor supply location, etc., the most appropriate sterilization conditions were identified. The temperature of the hotplate was varied from 55 °C to 75 °C and with this 20 °C increase in temperature, sterilization was completed in half the time. In this experiment, it was confirmed that the combined effect of a relative humidity (RH) of 0.5% and nitrogen gas was superior to the use of nitrogen gas alone. Furthermore, it was clarified that the optimal humidity was in the range of 0-5 % RH. When RHs of 0, 0.5 and 5% were tested, 0.5% RH was found to be optimal for sterilization. The location of the water vapor supply was changed relative to the hotplate, and use of the most remote port upstream of the reactor resulted in the most efficient sterilization. In addition, the results correlated with the amount of NO radicals generated. The NO radical is the precursor of OONO・- (peroxynitrite anion radical). The sterilization factors associated with this experiment were NO radicals, H2O2, OH radicals, O2・- (superoxide anion radicals) and OONO・-. Only OONO・- production correlated with sterilization efficiency. Therefore, OONO・- is thought to be the major factor for nitrogen gas plasma sterilization. In addition, as already described, the highest sterilization efficiency was with 0.5% RH and the amount of OONO・- produced correlated with the RH. These data support the idea that OONO・- is the major contributing factor for nitrogen gas plasma sterilization. The D values for this experiment were approximately 10 min.