An atmospheric low‐temperature microwave plasma torch has been developed and applied to disinfection. The size of the plasma output is relatively large (35 mm in diameter). Ar gas at a flow rate of 2.2 slm and 85 W microwave power are used. Plasma discharges are produced between the tip of each electrode and the inner surface of the cylinder. When an Escherichia coli culture is placed for 2 min at 20 mm below the torch, where the gas temperature is sufficiently cool, the bacteria are almost completely killed within a 40 mm diameter circle. The UV radiation is one of the major players responsible for killing bacteria, others being the reactive species and the charged particles.

A mechanism for sterilizing Escherichia coli by a flowing postdischarge and UV radiation of argon plasma at atmospheric pressure was investigated by analyzing the surviving cells and the potassium leakage of cytoplasmic material and by morphological observation. Inactivation of E. coli results from the destruction of the cytoplasmic membrane and the outer membrane under plasma exposure and the destruction of nucleic acids by exposure to ultraviolet radiation from the plasma source.

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Chemical characteristics and bactericidal properties of two low-temperature atmosphericpressure Ar plasma devices are investigated: one of them with UV and the other with almost no UV on treated samples. The control of the UV radiation is achieved by two nozzles. One has a straight shape, and the other has a 908-bent. The bent nozzle blocks the light produced inside the torch, whilst allowing the plasma gas to reach the samples. The use of the straight nozzle allows the treatment by both the plasma gas and UV. We demonstrate that even an almost UV-free plasma treatment has bactericidal properties. Our measurements suggest that reactive species represent the main bactericidal factor of our low-temperature plasma.