## 2 Materials and Methods
### CAP Equipment and Inactivation Procedure  
As mentioned before, two electrode configurations were used, i.e., a DBD and an SBD electrode. For both electrodes, the discharge was generated between two electrodes covered by a dielectric layer. The diameters of the electrodes were 5.5 and 5.0 cm for the DBD and SBD configuration, respectively. For both configurations, the dielectric layer had a diameter of 7.5 cm. An enclosure was provided around both electrodes to increase the residence time of the plasma species and to obtain a more controlled environment. Both enclosures (22.5 cm \(\times\) 13.5 cm \(\times\) 10 cm and 10 cm \(\times\) 10 cm \(\times\) 4 cm for the DBD and SBD electrode, respectively) were not airtight, which resulted in the presence of impurities from the environment. In case of the DBD configuration, the electrode gap was set at 0.8 cm and the sample (or the UV-TEC strip or the small volume of water) was placed between those electrodes. For the SBD configuration, on the other hand, there was no electrode gap and both electrodes were located on the top of the enclosure. Here, the sample (or the UV-TEC strip or the small volume of water) was placed below the two electrodes while ensuring a similar distance between the sample and the electrodes as was the case for the DBD. In Figure 1, a schematic representation of both electrode configurations has been included as well as a photographic image of both specifically used plasma set-ups.  
For all experiments, the plasma was generated in a gas mixture of helium (purity 99.996%, at a flow rate of 4 L/min) and oxygen (purity \(\geq\) 99.995%). Two different oxygen levels were examined, i.e., 0.0 and 1.0% (_v/v_), which resulted in oxygen flow rates of 0 and 40 mL/min, respectively. The plasma power supply transforms a low voltage DC input (0-60 V) into a high voltage AC signal (0-20 kV), at a frequency up to 30 kHz. As mentioned before, two different input voltages were examined, i.e., 13.88 and 21.88 V. Throughout this manuscript, the terms 'power of the discharge' or 'discharge power' will be used to refer to this change in input voltage. Depending on the applied electrode configuration and oxygen level, this resulted in eight different peak-to-peak voltages ranging between 2.5 and 8.0 kV and eight different dissipated plasma power values ranging between 1.5 and 7.0 W, respectively. These values can be observed in Table 1. In order to simplify the presentation and the interpretation of the results, the input voltages will be included on the different figures/graphs. Finally, for all experiments, the frequency was set at 15 kHz.  
Figure 1: Schematic representation and photographic image of the DBD and SBD electrode configurations used within this study.  
Finally, before energizing the high-voltage power source, the reactor chambers were flushed for 2 or 4 min (SBD and DBD, respectively) to ensure a homogeneous gas mixture. Samples, which were rinsed 3 times with sterile phosphate buffered saline (PBS) solution (to remove the remaining planktonic cells) and allowed to dry prior to treatment, were always treated for 10 min. This treatment time was selected based on the study of [PERSON] et al. [17], which proved that further inactivation could not be obtained if the treatment time was prolonged due to the occurrence of a tailing phase. For the UV-TEC strips and the small water volumes, a similar CAP treatment time was applied.