The authors would like to thank for this helpful comment. We changed the subsection as described below. With stating that argon-nitrogen mixtures mainly emit high amounts of radiation, the authors want to emphasize, that the sterilization efficiency is based on radiation rather than interaction of radicals with the sample. In low-pressure argon-nitrogen plasmas, the only significant possible radical is atomic nitrogen. As atomic nitrogen is not known for high etching efficiency towards organic materials, the main reason for inactivation of D. radiodurans is based on radiation effects. Furthermore, Argon-Nitrogen plasmas emit high amounts of radiation compared to Argon-Oxygen plasmas, as shown for example in [5]. The data in [5] is not comparable in absolute values, as the system was changed afterwards. Absolutely calibrated spectra were measured and have been submitted in another publication. The authors think that estimating the inactivation efficiency towards D. radiodurans based on the UV dose cannot be performed on a reliable bases due to the following reasons: First, the inactivation efficiency towards spores is not only depending on the overall dose of the emitted radiation, but especially on the dose per wavelength. This has been demonstrated by Munakata et al. for B. subtilis spores (Munakata et al., Photochemistry and Photobiology, Blackwell Publishing Ltd, 1991, 54, 761-768). To the authors’ knowledge, there is no publication measuring the wavelength depending inactivation efficiency of B. radiodurans in the VUV. Second, the samples are mixed with Mars Analog Soil and most of the samples are covered with it. This leads to a very inhomogeneous exposure of the samples which can only be estimated arbitrarily. To address the reviewer’s comments, subsection 2.3 has been modified as follows: An argon-nitrogen mixture (100:5 sccm) was used with continuous power of 500 W, as it emits significantly higher amounts of radiation in the bactericidal wavelength region from 100 nm to 400 nm compared to an argon-oxygen mixture (100:5 sccm) [5]. The absolute values presented in [5] are not applicable to the results shown here, due to modification of the plasma system concerning the power coupling. Nevertheless, the significantly higher emission of the argon-nitrogen mixture is shown. Absolute values of the radiation dose in the range from 100 nm to 400 nm of the system configuration used in this study were measured and submitted [6]. A possible radical that can interact with the samples is atomic nitrogen. As atomic nitrogen is not known for etching of organic materials, we assume that inactivation in the argon-nitrogen mixture is based on radiation effects. [6] Raguse, M.; Fiebrandt, M.; Denis, B.; Stapelmann, K.; Eichenberger, P.; Driks, A.; Eaton, P.; Awakowicz, P.; Moeller, R. Understanding of the importance of the spore coat structure and pigmentation in the Bacillus subtilis spore resistance to low pressure plasma sterilization. Submitted to Journal of Physics D: Applied Physics.
The plasma conditions are not described sufficiently. It is only stated that the argon-nitrogen mixture ‘mainly emits high amounts of radiation in the wavelength region from 100 nm to 400 nm’ without specifying what high fluences at the sample site are. The term amount is not applicable here. With the knowledge of the spectral irradiance in the UV range from 100 to 400 nm the authors could have made a calculation to estimate the inactivation of D. radiodurans by the UV component of the plasma.