Development of Oxygen Radical Sensor for Atmospheric Non-Equilibrium Microwave Discharge Plasma Jet

Presently, an atmospheric-pressure non-equilibrium microwave discharge plasma jet is expected to be applicable in the sterilization and disinfection equipment for dental implants. However, since the atmospheric-pressure plasma is in non-equilibrium state, there have been no simplified means established to measure basic properties of the plasma. We successfully developed a radical sensor, a simplified tool for detecting oxygen radicals released from plasma by using polyester fiber as base material, and methylene blue as dye. When this sensor detects an oxygen radical, the color of the radical sensor changes from blue, the original color, to white. In this report, we are going to explain the results of the experiments in the fabrication process to verify the behavior of this radical sensor. We combined polyester fiber, the base material of the radical sensor, and methylene blue, the dye, to prototype the radical sensor and used it in our experiments. The radical sensor features the mechanism in which the color changes from blue to white when plasma-irradiated. We used the angle meter to measure the hydrophilicity level and verified the etching effects of the oxygen radicals on the base material in order to clarify this discoloration mechanism. From this result, we found out that the hydrophilicity varied greatly as the flow rate of the oxygen gas used as plasma gas changed and that the color-changing mechanism was due to the adsorption effect of the oxygen radicals. We also used X-ray photoelectron spectroscopy (XPS) to analyze the components to further understand the adsorption effect of the oxygen radicals and clarified that the oxygen radicals accounted for the color-changing mechanism of the radical sensor.