## 3 Results
### Determination of the Effective Treatment Area  
The plasma treatment of agar plates inoculated with _S. aureus_ DSM 799/ATCC 6538 as a test microorganism resulted in the formation of inhibition zones (defined as areas without visible growth). The shape of the zone was circular for vertical treatment and became increasingly elliptical with increased tilting (Figure 5). The width and length of the zones decreased at least slightly (by 7-14%) and increased (by 30-36%), respectively, with rising incidence angle (Figure 6a,b). The total effective area increased with rising treatment time and tilting (Figure 6c). Thus, the effective area for a 50\({}^{\circ}\) tilt was 25% bigger than for the vertical treatment for 45 s.  
For the ROS, depending on the applied treatment axis, a circular or elliptic shape of the effective area was determined (Figure 7a,b). The plasma treatment of the starch-potassium iodide plates resulted in three effective zones which can be separated from the center to the outside into primary, secondary and peripheral zones. The primary zone was the area where the visible effluent had direct contact with the starch-potassium iodide plates. This zone was characterized by a dark brown to deep black spot. The secondary zone had a brownish color and was formed directly around the primary zone. The peripheral zone was a diffuse dark yellow area on the outside. These different zones can be separated by a Matlab program resulting in a false color photo with the primary zone in green, the secondary zone in blue and the peripheral zone in red (Figure 7c,d). Depending on the applied treatment axis, the zones were circular or elliptic with a comet-like shape. If the samples were treated vertically, a circular effective area was obtained which was characterized by all three zones (Figure 7a,c). With increasing tilting of the kINPen(r) MED-\(\beta\), the shape of the effective zones became increasingly comet-like with an intense center spot and an expanding tail (Figure 7b,d). The correlation between the antimicrobial efficacy and the ROS determination (Figure 8) showed that the width between the secondary and the peripheral zone and the length of the inhibition zone were similar to the peripheral zone of the ROS formation (for 45 s and 0\({}^{\circ}\), 25\({}^{\circ}\), 50\({}^{\circ}\)). Figure 5: Effective treatment area of kINPen® MED-\(\beta\) visualized by inhibition zone assay at 8.5 mm distance after 45 s plasma treatment for (**a**) perpendicular treatment and (**b**) an incidence angle of 50\({}^{\circ}\) (side 1: inclination of the kINPen® MED-\(\beta\) as shown in Figure 2c, side 2: area with plasma plume propagation); test bacterium: _Staphylococcus aureus_ DSM 799/ATCC 6538). The total area of the inhibition zones (_S. aureus_) increased (Figure 6c) whereas ROS decreased slightly by 9% with rising incidence angle (Figure 9). Thus, the total area of the inhibition zone in the antimicrobial assay for 50\({}^{\circ}\) was 16% larger than that of the ROS analysis. The data obtained from VUV irradiation tests for different treatment angles showed that the excited fluorescent dye for VUV emitted green light in a circular shape for a vertical treatment. The excited fluorescent dye for VUV emitted green light in a circular shape for a vertical treatment (Figure 10a). In the case of a tilted treatment despite central positioning of the plasma jet, the impact point of the radiation shifted slightly to the right due to the additional shielding window on top of the dye (Figure 10). It was expected that the plasma would propagate slightly on top of the shielding window and hence the impact point would move further. Thus, the formed shape of the excited area is rather an inverse comet compared to the area for ROS. In the case of UV, the fluorescent dye emitted blue light (Figure 10b) in similar shapes to the VUV tests (Figure 10a), while the overall area was much larger for the UV test. Three zones could also be separated from the center to the outside into primary, secondary and peripheral zones (Figure 10c,d).