Five gaseous reactive oxygen and nitrogen species (RONS) density generated by microwave plasma jet

Microwave plasma jets based on a coaxial transmission line resonator show outstanding advantages such as portability, lower power consumption, and low-temperature operation. In this manuscript, the most important of the five gaseous reactive oxygen and nitrogen species (RONS) densities including OH, O, O₃, NO, and NO₂ densities are measured synchronously, while the plasma jet is treating a biological tissue under different discharge parameters (gas composition, gas flow, skin humidity, and output power). It has been found that the gas composition and the output power are two key factors to regulate the dose of RONS concentrations. For the OH concentration, water vapor in the gas flow plays an important role. By changing the microwave power and the gas composition, the OH concentration changes from 0.4 × 10¹⁴ cm^-3 to 5.54 × 10¹⁴ cm^-3. O is mostly affected by the O₂ percentage in Ar, and 1% percentage is the optimal value. O₃ is proportional to the O₂ percentage in Ar, and 2% O₂ can get a maximum O₃ density of 6.9 × 10¹⁶ cm^-3. NO is in the range of 2 × 10¹³ cm^-3 to 5.4 × 10¹⁴ cm^-3, and NO₂ is in the range of 5.5 × 10¹⁴ cm^-3 to 5 × 10¹⁵ cm^-3. The increase in the humidity of the skin has a positive effect on the concentration of OH, O₃, and NO while a negative effect on the O and NO₂ concentration. For the normal skin with a humidity of 40%, the concentrations of the long lifetime species like O₃ and NO₂ are almost 10^1-2 times those of the other reactive species. This research provides parameter setting guidance for different RONS requirements.