## 3 Results and Discussion
### In Vitro Cytotoxic Effect on Cancerous Cell Lines Using Synthesized AgNPs  
The preparation of NPs that can eradicate cancerous cells while leaving normal cells unharmed will be a crucial step towards improving harsh toxicities linked with drug administration. In vitro cytotoxicity analysis is a valuable tool for screening synthesized compounds with potential anti-cancer activity. The MTT assay evaluated the level of cell death. MTT is reduced in the mitochondria, and the absorbance measured is suggestive of the mitochondrial activity of the cell population, and hence the amount of viable cells [121]. As shown in Figure 11A-C, the percentage of cell survival for all synthesized extracts were dose-dependent. All AgNPs at various concentrations showed high cytotoxicity against all cell lines (Figure 11A-C). NPs can efficiently enter the tumor micro-environment and prevent cancer cells from metastasizing [122; 123; 124]. Controls 1, represented 100% of viable cells, while control 2 contained DMSO only. For HEK293, the highest cellular viability was observed at 15 \(\upmu\)g/mL when treated with the powdered leaf and stem AgNPs. Furthermore, at 240 \(\upmu\)g/mL, the lowest percentage for cell viability was observed in the fresh stem AgNPs (Figure 11A). Medium-high cytotoxicity was observed with the synthesized NPs even at lower concentrations (15 \(\upmu\)g/mL). The percentage of cellular viability for HeLa was highest at 15 \(\upmu\)g/mL when exposed to the powdered stem AgNPs, whereas at 240 \(\upmu\)g/mL the lowest viability was observed when exposed to the methanol stem AgNPs (Figure 11B). The percentage viability for the MCF-7 cell line was greatest at 15 \(\upmu\)g/mL when exposed to the powdered stem AgNPs, and lowest at 240 \(\upmu\)g/mL when treated with the methanol stem and fresh leaf AgNPs (Figure 11C). Cell viabilities were above 30% for most NPs at varying concentrations (Figure 11A-C). As the NP concentration increased, so did their toxicity for the cell lines. Statistical analysis showed that all extracts had significantly different activities across all concentrations (\(p<0.05\)). Figure 11: The in vitro cytotoxicity assessment (% cell viability) of silver nanoparticles (AgNPs) derived from the leaf and stem extracts of _B. albostellata_. (**A**) HEK293 human embryonic kidney cells; (**B**) HeLa cervical carcinoma cells; (**C**) MCF-7 breast adenocarcinoma cells. (* \(p\) <0.05 and **_p_ <0.001 were deemed statistically significant across the varying concentrations, ranging from 15 to 240 \(\upmu\)g/mL). The results are expressed as means \(\pm\) standard deviation (SD), with \(n\) = 3, and represented as a percentage relative to the control sample. Control Leaves 1—cells only; Control Stems 1—cells only; Control Leaves 2—DMSO control only; Control Stems 2—DMSO control; LM—Leaf methanol extract; SM—Stem methanol extract; FL—Fresh leaf material; FS—Fresh stem material; PL—Ground leaf powder; PS—Ground stem powder. The IC\({}_{50}\) values of the synthesized AgNPs in the three mammalian cell lines are represented in Table 6. Significant cytotoxic activity was observed in the HEK293 cell line upon exposure to the methanol leaf AgNPs, with an IC\({}_{50}\) value of 9.02 \(\upmu\)g/mL. However, lower cytotoxicity was found in the stem AgNPs (61.66 \(\upmu\)g/mL). Fresh leaf and stem AgNPs displayed moderate cytotoxicity in the HEK293 cell line (IC\({}_{50}\) 47.86 and 33.04 \(\upmu\)g/mL), while lower cytotoxic levels were observed for the powdered leaf and stem AgNPs (IC\({}_{50}\) 100 and 61.24 \(\upmu\)g/mL) (Table 5). Methanol leaf and stem AgNPs displayed the highest cytotoxicity in the HeLa cell line, with IC\({}_{50}\) values of 5.87 and 12.58 \(\upmu\)g/mL, respectively. Fresh leaf and stem AgNPs displayed moderate cytotoxicity in the HeLa cell line (IC\({}_{50}\) 29.64 and 32.14 \(\upmu\)g/mL), whereas lower cytotoxic levels were observed in the powdered leaf and stem AgNPs (IC\({}_{50}\) 69.18 and 54.70 \(\upmu\)g/mL) (Table 6).