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

Abstract—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 nonequilibrium
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 a 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
the 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.