## 3 Results and Discussion
### Biological Assessments  
#### 3.3.1 Antioxidant Activity  
The potential antioxidant activity was assessed for silver metallic/bimetallic nanoparticles via DPPH\({}^{\bullet}\) free radical assay. The IC\({}_{50}\) values were calculated in mg/mL by applying the exponential curve that involved a relationship between the sample concentrations versus the percentages of the remaining DPPH\({}^{\bullet}\)[56]. The results (Figure 6) verified that the _Beta vulgaris_ L. extract revealed the most potent activity for scavenging the DPPH\({}^{\bullet}\) free radical with IC\({}_{50}\) at 0.299 \(\pm\) 0.073 mg/mL. The antioxidant capacity of the extracted _Beta vulgaris_ L. was much greater using the higher concentration of the sample, and thus 74.7% inhibition was calculated at 0.902 mg/mL, while the antioxidant capacity was reduced to 32.77% at the lower concentration (0.113 mg/mL). It was noticed that the inhibition efficiencies of the tested metallic and bimetallic nanoparticle solutions were reduced compared to the aqueous extract of _Beta vulgaris_ L. Accordingly, the Ag-mNPs revealed an IC\({}_{50}\) value at 0.404 \(\pm\) 0.067 mg/mL, and then the antioxidant capacities were reduced again in the case of bimetallic nanoparticles, for instance, the Ag-TiO\({}_{2}\) bmNPs (IC\({}_{50}\) = 0.797 \(\pm\) 0.063 mg/mL) and Ag-SeO\({}_{2}\) bmNPs (IC\({}_{50}\) = 1.473 \(\pm\) 0.104 mg/mL). At the higher concentrations of the prepared nano-solutions, Ag-mNPs revealed a percentage of inhibition at 52.9% (1.958 mg/mL), the Ag-TiO\({}_{2}\) bmNPs revealed a percentage of inhibition at 58.08% (1.099 mg/mL), and Ag-SeO\({}_{2}\) bmNPs revealed a percentage of inhibition at 46.04% (1.351 mg/mL). The free radicals of DPPH\({}^{\bullet}\) (a purple color) in the solution tended to stabilize via reactions with antioxidant molecules that are rich in stable radical sources. The stabilization of DPPH\({}^{\bullet}\) free radicals changed the purple color of DPPH into colorless at the higher sample concentrations. The ability of the tested sample to scavenge the free radicals of DPPH\({}^{\bullet}\) in the solution indicated the antioxidant capacity. In the case of _Beta vulgaris_ extract, the hydroxyl groups provided stable hydroxyl radicals that trapped the free radicals of DPPH\({}^{\bullet}\). The reactive oxygen and nitrogen species in the extracted components of the plant extract are the factors that increase the antioxidant capacity. Also, the phenolic components, as estimated from the phytochemical analysis, enable the trapping of the free radicals of DPPH\({}^{\bullet}\). The phenolic components provided stable free radicals via the delocalization of the radical on the phenyl ring. Our results agree with the recently reported work by [57]. The release of hydrogen atoms in the antioxidant mechanism can be termed as specified in Figure 7.  
On the other hand, the antioxidant activity of aqueous _Beta vulgaris_ extract and silver metallic/bimetallic nanoparticle solutions was also assessed via phosphomolybdate assay (Tables 1 and S3). The results verified that the _Beta vulgaris_ extract displayed the most potent activity with total antioxidant capacity (TAC) at 2388.524 \(\pm\) 7.226 (mg AAE/100 gm DS). The antioxidant activity was reduced for the Ag-mNPs (TAC = 1326.292 \(\pm\) 8.835 mg AAE/100 gm DS) than the plant extract. The order of the antioxidant potency of the  
Figure 6: The antioxidant results via DPPH assay: (**a**) Plotted % scavenging activity versus sample concentration. (**b**) A comparison of the antioxidant results. samples was found that the aqueous extract was much more potent than Ag-mNPs or Ag-TiO\({}_{2}\) bmNPs, and Ag-SeO\({}_{2}\) bmNPs was the last in the order of potency. These results were matched with the antioxidant potency estimated via the DPPH free radical assay. The process relies on the reduction of phosphomolybdate ions in the presence of an antioxidant, leading to the creation of a green phosphate/MoV complex. This complex is then quantitatively measured using spectrophotometry.