Effects of the physical parameters of a microwave plasma jet on the inactivation of fungal spores

• We developed a microwave plasma jet source for biological application.
• We identified the physical conditions of plasma inhibiting fungal growth.
• We demonstrated that plasma effects could be varied among different fungal species.

In spite of their importance in human life, filamentous fungi have not been actively explored in the application of plasma to them. A plasma jet source at the atmospheric pressure was excited by 2.45 GHz microwaves and operated at low energy regime with an average power of 0.8 W–1.6 W. This microwave plasma was applied to examine fungal inactivation and find physical conditions of plasma (electrical power, pulse widths, and fed gases) at which the highest inhibition effects on fungal growth was achieved. Spore germination and hyphal growth of the fungus were dramatically decreased when oxygen was used in the plasma discharge, and this might be due to the elevation in the level of Oxygen (O) radical. The level of O radical in the plasma generated from Ar and oxygen was also enhanced by the increased power and pulse width. Hyphal growth of the fungus was more inhibited when greater power or longer pulse was applied. It appears that plasma effects were varied among different fungal species. Different levels of inhibition on spore germination and growth of three filamentous fungi, Neurospora crassa, Fusarium graminearum, and Fusarium oxysporum was observed.