# Antibacterial Activity of Green Synthesised Silver Nanoparticles on _Saccharomyces cerevisiae_
## 3 Results and Discussion  
The absorption spectra of the samples obtained from the aqueous yeast extract were analysed (Figure 1). The sample marked as control was a 20% glucose solution. All spectra had an absorption peak of approximately 400 nm. However, the highest peaks were from samples to which silver nitrate had been added at concentrations of 0.5 mM and 1.0 mM. The values of optical density in these peaks were 1.17 and 1.34 respectively, which was 1.8 and 2.2 times higher than the control sample. The next step was to analyse the absorption spectra of the samples obtained from the supernatant. An interesting fact was that the levels of optical absorption of the samples in this study were much higher than in the study of samples of yeast lysate (Figure 2). Again, the highest peaks were shown in samples where silver nitrate concentrations of 0.5 mM and 1.0 mM were used. In these samples, the values of optical density were 9.88 and 8.52 respectively, which were 1.8 and 1.7 higher than the values in the control sample. Furthermore, it should be noted that the values of the optical density of the samples to which silver nitrate had been added at concentrations of 1.5 mM and 2.0 mM were below that of the control sample. Figure 1: The absorption spectrum of samples obtained from yeast extract. The yeast extracts were obtained from samples of yeast _S. cerevisiae_ 7 IB cultured in 20% glucose solution with the addition of: (1) sterile dH\({}_{2}\)O, (2) 0.5 mM AgNO\({}_{3}\), (3) 1.0 mM AgNO\({}_{3}\), (4) 1.5 mM AgNO\({}_{3}\) and (5) 2.0 mM AgNO\({}_{3}\). Figure 2: The absorption spectrum of samples obtained from the supernatant. The supernatants were obtained from samples of yeast _S. cerevisiae_ 7 IB and cultured in 20% glucose solution with the addition of: (1) sterile dH\({}_{2}\)O, (2) 0.5 mM AgNO\({}_{3}\), (3) 1.0 mM AgNO\({}_{3}\), (4) 1.5 mM AgNO\({}_{3}\) and (5) 2.0 mM AgNO\({}_{3}\). The optical density values in the peaks were compared in samples to which silver nitrate was added at concentrations of 0.5 mM and 1.0 mM to the yeast lysate and supernatant. The optical density of the supernatant was 8.5 times higher for a concentration of 0.5 mM and 6.2 times higher for a concentration of 1.0 mM. The data obtained indicated that the supernatant contained more silver nanoparticles than the yeast lysate. Furthermore, the most effective concentrations were found to be 0.5 mM and 1.0 mM. The results of studies of the spectra of samples correlated with numerous studies on the biosynthesis of silver nanoparticles. For example, silver nanoparticles obtained by biosynthesis using yeast extract as a reducing and capping agent had an absorption peak of 400 nm [12]. In another study, nanoparticles were obtained from _Rumex hypernosedus_ extract, a plant widespread in large areas of North America. The absorption peak of these nanoparticles was 425 nm, which corresponded to the absorption through surface plasmon in silver nanoparticles [13]. Another work described the synthesis of silver nanoparticles by the yeast strain _Saccharomyces_ Sp. BDU-XR1, which was isolated from spontaneous yogurt used in Azerbaijan. The peak of the absorption spectrum of nanoparticles was found in the range of 410-420 nm in a UV spectrophotometer [14]. Thus, compared with the results obtained here, it can be concluded that the supernatants and yeast lysates obtained contained silver nanoparticles. Of course, additional research would be needed to confirm this, but this study confirmed that the supernatant probably contained more nanoparticles of silver than the yeast lysate. Using a qualitative reaction, the approximate concentration of silver ions in each of the samples was determined. The summary results are presented in Table 1.  
In addition, the probability of the results was checked using the Wilcoxon test, which produced interesting results.