Subatmospheric Pressure Microsecond Spark Discharge Plasma Jet for Surface Decontamination

For safe handling and transport, the exterior surfaces of a container used to collect microorganisms should be disinfected. Though conventional methods are highly reliable, they could damage the container or destroy the contents, rendering the collection of microorganisms pointless. In this paper, a pulsed subatmospheric pressure microsecond spark discharge plasma jet, referred to as a pin-to-hole discharge (PHD), was used as a source of ultraviolet (UV) radiation and reactive oxygen and nitrogen species (RONS) for the sterilization of inoculated surfaces with limited thermal impact. A device was created to generate an overlapped region of treatment on a cylindrical body from an array of these PHDs. The surface was inoculated with vegetative bacteria (Escherichia coli), sporulated bacteria (Bacillus atrophaeus), or a simulated dirt and spore solution and then treated with the plasma array. Gas composition effects on the bacterial load reduction were explored, and the combination of RONS from air was found to be an improvement of the effects from pure oxygen. Increasing treatment time caused an increase in bacterial load reduction, regardless of the distance or gas composition. Treatment of simulated soil inoculation showed suppressed sterilization results which asserted the fact that addition of UV radiation from the discharges improved bacterial inactivation from PHDs. The radial array of pulsed subatmospheric pressure microsecond spark discharges was shown to reduce the bacterial load on the inoculated surface by 5-log within 20 min of treatment from a discharge in air.