Bactericidal Effect of Nanopulse Generated Plasma on <italic>Bacillus subtilis</italic> Spores at Different Humidity Levels

Abstract

The antimicrobial properties of non-thermal plasma (NTP) offer promising applications in sterilizing temperature-sensitive materials. This study investigates how treatment parameters affect the inactivation of Bacillus subtilis spores using a surface dielectric barrier discharge powered by a nanopulse supply. This setup enables NTP exposure without direct sample contact and under controlled conditions. The effects of sample distance (3−45 mm), exposure time (5–30 min), and relative humidity (RH) (40%–90%) were evaluated. Sporicidal activity was assessed using a previously established protocol, and gas-phase species in NTP were analyzed by Fourier-transform infrared spectroscopy (FTIR). All parameters significantly influenced inactivation. Notably, 90% RH led to up to 4-log greater spore reduction, highlighting the critical role of humidity in enhancing NTP efficacy.