# Antioxidant Properties of Selenium Nanoparticles Synthesized Using Tea and Herb Water Extracts
## 3 Results and Discussion
### Synthesis and Characterization of SeNPs
In each case, there are also particles with dimensions of about 100 nm in the suspension, which is consistent with the spectrum, but the fraction of dominant SeNPs is significantly smaller than this value. With increasing concentration of the extract, an increase in the dimensions of the SeNPs was observed. The value of R\({}^{2}\) for this dependency is 0.735. When the synthesis is carried out at a constant concentration of mint extract and increasing concentration of selenium, a decrease in the size of SeNPs was recorded. There is a clear relationship with the coefficient R\({}^{2}\) equal to 0.709. In each case, however, the obtained nanoparticles are larger than 100 nm and are, respectively: for Se/mint ratio 1:1- 188.4 \(\pm\) 6.35 nm, 2:1- 166.6 \(\pm\) 4.75 nm, 3:1- 144.5 \(\pm\) 5.10 nm, and 4:1- 125.9 \(\pm\) 3.95 nm. The determined SeNPs values from DLS analysis are consistent with the obtained UV-Vis spectrum. The spectra of the nanoparticle suspensions obtained from the synthesis with the use of tea infusions suggest a high inhomogeneity. Using green tea extract, only at a 1:1 reagent ratio, the size of the dominant fraction is below 100 nm, namely 50.0 \(\pm\) 3.20 nm. The remaining fraction of nanoparticles has particles with sizes larger than 120 nm. Increasing the concentration of the extract in the reaction mixture increases the size of the obtained nanoparticles, from 125.9 \(\pm\) 4.3 nm (1:2 ratio) up to 288 \(\pm\) 10.5 nm (1:4 ratio). The correlation coefficient R\({}^{2}\) for this relationship is high and amounts to 0.806. Increasing the concentration of selenium also causes a significant increase in the size of the nanoparticles, but in this case, there is no clear correlation between these parameters. In all cases, their sizes are significantly higher than 100 nm (for a 4:1 ratio, size of 125.9 \(\pm\) 11.3 nm) or even higher than 200 nm (at 2:1 and 3:1 ratios). These relationships were quite visible in the UV-Vis spectrum, where an increase in the intensity of the absorption band was observed at wavelengths higher than 300 nm (it is \(\lambda_{\rm max}\) for SeNPs with dimensions of 100 nm according to [PERSON] [38]). Synthesis with black tea produced nanoparticles smaller than 100 nm only in the case of a four-fold excess of Se and the size of their dominant fraction was 95.5 \(\pm\) 3.75 nm. With the reagent concentration ratio of 1:1, nanoparticles with dimensions of 131.8 \(\pm\) 10.2 were observed in DLS analysis. Further increasing the concentration of reagents increases the size of the SeNPs (except for the aforementioned 4:1 ratio). It should be noted that the main problem of the synthesis using black tea infusion is the lack of homogeneity of the obtained nanoparticles. They are differentiated in terms of size, with the predominance of those remarkably larger than 100 nm, which significantly limits their potential use in medicine. Apart from size, another important parameter characterizing SeNPs is polydispersity index (PDI). It is used estimate the average uniformity of a particle solution. From the point of view of antioxidant capacity, it is also very important. In our previous work, we postulated that the greater the homogeneity of nanoparticles, the higher their antioxidant capacity [44]. According to the theory, the sample can be considered as monodisperse when the PDI value is less than 0.1. The PDI values for all SeNPs obtained are summarized in the Table 2.  
For most of the obtained SeNPs, the PDI values were high, which proves their lack of monodispersity. There is no relationship between the concentration of the infusion used for SeNPs synthesis and the PDI value. Surprisingly, the lowest PDI values were obtained for SeNPs synthesized at a two-fold excess of plant extract in relation to selenium. These values were close to 0.1 and amounted to 0.129 for SeNPs obtained from green tea, 0.109 from chamomile, 0.105 from black tea, and 0.082 from mint, respectively.