# Antioxidant Properties of Selenium Nanoparticles Synthesized Using Tea and Herb Water Extracts
## 3 Results and Discussion
### Synthesis and Characterization of SeNPs  
The synthesis of SeNPs was conducted parallel by the reduction of sodium selenite with tea or herbal infusion. The synthesis was carried out in two ways: with an increasing concentration of the plant extract with a constant concentration of selenium salts, and in the second variant with an increasing concentration of selenium salts and a constant concentration of the infusion. The recorded UV-Vis spectra of obtained nanoparticles are shown in Figure 2. The presented spectra are similar to those described by us earlier [42]. We also observed a decrease in absorbance at the wavelength of 330 nm. It should be noted that the spectra were recorded using a tea infusion as a blank. The infusion was of the same concentration as that in the reaction mixture. Absorbance less than zero may suggest that the blank absorbs more light than the sample; in other words, the blank has a more intense colour than the sample. In the case of the study of the post-reaction mixture, this is understandable, as the compounds determining the color of the tea may be consumed during the synthesis of SeNPs. The main pigments in fresh tea leaves are chlorophyll and carotenoids. These pigments may condense as they wither and oxidize, becoming darker. During oxidation, the green color of tea's chlorophyll turns black. This leads to the dark color of oxidized teas. The negative absorbance may be evidence that these two groups of compounds are also involved in the reduction of selenium salts to selenium in the form of nanoparticles. It has been proven that UV-Vis spectra of nanoparticles can provide valuable information regarding their size [38]. The basis of this method is the fact that with the increase in the size of nanoparticles, the colour of their suspension changes from yellow (for SeNPs with dimensions of about 20 nm) to red (size of about 100 nm). This entails a shift of the absorption maximum in the UV-Vis spectrum towards higher wavelengths. UV-Vis spectra recorded for SeNPs suspensions obtained by synthesis using chamomile infusion show a maximum at a wavelength of about 400 nm. According to the method proposed by [PERSON] [43], it should be assumed that they have dimensions of about 120 nm. The performed DLS analysis confirmed these assumptions; the suspension is dominated by the fraction with dimensions of 125.9 \(\pm\) 5.31 nm at a 1:1 reagent ratio. The increasing ratio of reactants does not change the size of the obtained nanoparticles. Only with the increase in the concentration of chamomile infusion, the intensity of the absorption band at the wavelength of 400 nm increases, which may suggest an increase in the concentration of nanoparticles with dimensions of about 120 nm (Figure 2). With the increase in the concentration of the extract, the homogeneity of the obtained nanoparticles increases, but the formation of those with dimensions larger than 100 nm is preferred. In our previous work, it has been proven that the antioxidant capacity of nanoparticles is influenced not only by their size but also by their homogeneity [44]. Thus, obtaining nanoparticles with similar dimensions seems to be beneficial from the point of view of their antioxidant capacity but not necessarily from the point of view of their potential biomedical applications as they must be smaller than 100 nm to cross cell membranes. Figure 2: The UV–Vis spectra of synthesized selenium nanoparticles. In the case of mint extract at a 1:1 reagent ratio, larger nanoparticles of 188.4 \(\pm\) 6.35 nm were found. By doubling the concentration of mint extract (1:2 ratio), nanoparticles with much smaller dimensions of 63.1 \(\pm\) 3.0 nm are obtained. A further increase in the concentration of the extract increased the dimensions of the obtained SeNPs (ratio 1:3-72.4 \(\pm\) 4.20 nm and 1:4 nm 95.5 \(\pm\) 6.31). These results come from the DLS analysis; it should be emphasized that this is not visible on the UV-Vis spectrum.