Sterilization of Surfaces with a Handheld Atmospheric Pressure Plasma

Low temperature, atmospheric pressure plasmas have shown great promise for decontaminating the surfaces of materials and equipment. In this study, an atmospheric pressure, oxygen and argon plasma was investigated for the destruction of viruses, bacteria, and spores. The plasma was operated at an argon flow rate of 30 L/min, an oxygen flow rate of 20 mL/min, a power density of 101.0 W/cm³ (beam area = 5.1 cm²), and at a distance from the surface of 7.1 mm. An average log reduction of viable spores of 10 was obtained after only 20 seconds of exposure to the reactive gas. By contrast, it takes more than one hour to kill anthrax in an autoclave. The plasma properties were investigated by numerical modeling and chemical titration with nitric oxide. The numerical model included a detailed reaction mechanism for the discharge as well as for the afterglow. It was predicted that at a delivered power density of 29.3 W/cm³, 30 L/min argon, and 0.01 volume% O₂, the plasma generated 1.9 x 10¹⁴ cm^-3 O atoms, 1.6 x 10¹² cm^-3 ozone, 9.3 x 10¹³ cm^-3 O₂(1Δg), and 2.9 x 10¹² cm^-3 O₂(1Σ+g) at 1 cm downstream of the source. The O atom density measured by chemical titration with NO was 6.0 x 10¹⁴ cm^-3 at the same conditions. It is believe that the oxygen atoms and to a lesser extent the O₂(1Δg) metastables were responsible for killing the anthrax and other microorganisms.