## 3 Results and Discussion
Each storage medium in this figure consisted of eight portions of non-chemically treated unirradiated samples and measured in the same way as the irradiated samples, as described in Figure 5. It may be observed that the median intensity of the background signals in both storage conditions were all at the same level, but the data sets between the two mediums showed a very different distribution view. One can also notice from the plots in Figure 6 that the background signals obtained from the freezer-stored samples span much the same range of values and were more variable than in the vacuum-stored samples. Moreover, some individual outlying data points can be seen in the vacuum-stored samples which may be caused by intra-individual variations within the group of samples. Nevertheless, the stability of the background signals observed in storage conditions with either low humidity at room temperature or low humidity at sub-zero temperature can be regarded as good overall, and conclusions regarding the effect of low or lack of oxygen to the signal stability were equivocal and formed the needs of further scrutiny. Figure 7 compares the intra-individual variations of the ESR signal peak-to-peak amplitude (App) measured before and after treatment with DTT in unirradiated fingernail samples stored in the (a) vacuum chamber and (b) freezer. Each storage consisted of four sample collections and the time interval between sample collections was 2 weeks. Each experimental data point shown in this plot is an average of spectral measurements on three portions of unirradiated fingernail samples obtained from a single donor, and the reported errors are the standard deviation. The background signals of the samples were measured as the peak-to-peak intensity from the main singlet of the ESR spectra. Measurements were taken prior to chemical treatment, soon after the corresponding drying conditions in the chemical treatment process, and at 1, 2, 3, and 7 days after chemical treatment. Figure 4.0 Distribution of the ESR signal peak-to-peak amplitude (App) from non-chemically treated unirradiated fingernail samples stored inside the (**a**) vacuum chamber with 2% air humidity at 20 \({}^{\circ}\)C and (**b**) freezer with 3% air humidity at -20 \({}^{\circ}\)C recorded at different times. As seen in this figure, there was a significant intra-individual variation in the recorded initial background signals between the samples from the same individual, whereupon no pre-treatment was applied. After application of DTT treatment, however, the background signals were observed to be broadly consistent with each other, giving rise to the opportunity to correct for such uncertainties in the intra-individual variations within the same group of samples. Furthermore, the recorded App of the native background signals have been reduced and are quite stable over the 24 h time delay between chemical treatment and storage of the samples: no substantial gain in the peak-to-peak intensity was encountered in both storage conditions. This finding is interesting and could be useful as many of the previous studies advanced differing views that pre-existing native background signal tends to grow after drying in ambient air conditions and thus cannot be entirely removed in the spectra [42]. Further investigations into this notable observation should be made with applications of other antioxidant materials that could have similar effects.