Plasma generated from pure air and air-Ar ambient conditions produced various reactive species identified following optical emission spectroscopy (OES) analysis (Fig. XX). The results show that the Reactive Nitrogen Species (RNS) which is corresponding to ~300-400 nm from excited N2 molecules is the primary component generated under pure air plasma ambient. On the other hand, there was significantly increasing of both Reactive Oxygen Species (ROS) from excited Ar molecule which is corresponding to ~600-900 nm wavelength under air mixed with Ar.
It has been known that the cold plasma is generated by subjecting gas to high energy (electric voltage) at atmospheric pressure that ionizes the gas resulting in the formation of reactive species, electrons, and ultraviolet light (>300 nm) [20]. The reactive species such as Reactive Oxygen Species (ROS) and Reactive Nitrogen (RNS) play a significant role in biochemistry interaction due to the oxidation−reduction (redox) processes, especially in therapeutic roles in aerobic and plant biology. ROS and RNS have been shown to pose a broad spectrum of biological functions (from harmful to beneficial) depending on the dose and the species of organism exposed [1–4]. In eukaryotic microorganisms such as fungi, ROS regulates hyphae growth and differentiation of conidia and fruiting bodies [10–13], and fungal development is associated with changes in ROS levels. Plasma treatment did not affect plant health (or growth) and gene upregulation may have been due to the production of ROS and RNS that have been shown to activate plant resistance mechanisms [51– 53]. Therefore, the overall result suggest that the atmospheric hybrid cold plasma under air-Air ambient is more efficient than pure air ambient for modifying the surface wettability, resulting in water imbibition enhancement (see Optical emission spectra (OES) during plasma operation figure). In this work, however, UV interaction is not considered to be the primary mechanism for surface modification and microorganism deactivation because of low energy supply and ultrathin penetration depth which is in agreement with the literature reports.