# Dry Bio-Decontamination Process in Reduced-Pressure O\({}_{2}\) Plasma
## 3 Results  
### Decontamination Effect of UV Radiation in Oxygen Plasma  
The decontamination efficiency of oxygen plasma total and UV radiation individual (excluded the charge particles and free radicals generated by plasma discharge using the LiF) was investigated at the same operation parameters, respectively, from E as functions of plasma RF power, treatment time and gas flow rate. The samples were positioned at the center of the induction coil in the Pyrex glass tube of the reactor. Figure 2 shows the comparison of both the decontamination effects of oxygen plasma total and UV radiation individually. From Figure 2, for one thing, it could be clearly seen that the E of oxygen plasma total showed a strong dependence on the conditions mentioned above, and the effective bio-decontamination was carried out when oxygen plasma discharge under the conditions of 100 W, 60 s and 40 cm\({}^{3}\cdot\)min\({}^{-1}\), where the E was largest, up to 3.42.  
Figure 2: _Cont._  
In addition, the decontamination rate of _E. coli_ by oxygen plasma as a function of O\({}_{2}\) flow rate increased firstly (\(p<0.05\)) and subsequently decreased (\(p<0.05\)) with the increase of gas flow and was optimal at a flow rate of 40 cm\({}^{3}\cdot\)min\({}^{-1}\). This phenomenon was due to the inactivation effect of _E. coli_ depending on the average energy, number, and residence time of reactive species in the discharge zone. Reactive species had higher average energy and longer residence time in discharge zone at low flux than high flux, however, the number of species were limited, as opposed to high flow rate, which directly affected the performance of plasma on microbial inactivation. For another thing, the E of UV radiation individual changed only within a narrow range, from 0.4 to 1.5, in the whole process no matter how many changes these conditions underwent. These values indicate that during effective bio-decontamination, the contribution of UV radiation to decontaminating features of the oxygen plasma is less. This conclusion is also confirmed by the following.  
It is known that UV radiation kills bacilli through destroying the DNA of cells. So, we investigated the state of DNA after oxygen plasma treatment in order to further ascertain the effect of UV radiation on _E. coli_. Figure 3 displays the DNA agarose electrophoresis of _E. coli_ after three treatment conditions such as control, UV radiation individual and plasma total treatment at 100 W power, 60 s treatment time and 40 cm\({}^{3}\cdot\)min\({}^{-1}\) oxygen flow rate. As far as we know, if the skeleton of DNA is destroyed to generate small DNA fragments or light molecular DNA when exposes _E. coli_ to UV radiation or plasma [22; 23], which will produce tail phenomena during the DNA agarose electrophoresis [24]. But the diagrams in Figure 3 (2), which were treated by UV radiation individually, indicate that there are only fewer tail phenomena compared to oxygen plasma total Figure 3 (3). This result makes sure again that UV radiation in oxygen plasma slightly acts on bacilli during bio-decontamination process.  
Figure 2: Comparison of the decontamination effect between oxygen plasma total and UV radiation individual under different treatment conditions (**a**) Time 60 s, O\({}_{2}\) flow 40 cm\({}^{3}\cdot\)min\({}^{-1}\), Pressure 45 Pa; (**b**) Power 100 W, O\({}_{2}\) flow 40 cm\({}^{3}\cdot\)min\({}^{-1}\), Pressure 45 Pa; (**c**) Power 100 W, Time 60 s, Pressure 45 Pa. Capital letters A–E are distinguished from a–d to represent statistical significance in direct exposure.