*2.1. Biosynthesis of Se-NPs*

Se-NPs were produced using *Bacillus megaterium* culture supernatant (as reducing and stabilizing agents). Bacteria were subcultured on nutrient broth media in conical flasks and incubated with shaking aerobically at 37 ◦C for 48 h. After an incubation period, the bacterial cells were removed from the suspension by filtration through a 0.44 µm PVDF filter; then, they were centrifuged at 10,000 rpm to remove occasional bacterial cells and

macromolecules [33]. The next step was mixing cell-free supernatant with the selenious acid suspension (1 mM) by quotient (1:1) *v*/*v*. The mixtures were stirred at a controlled room temperature of about 25 ◦C. The process of selenious acid reduction was monitored by color change of the cell-free supernatant from colorless to reddish color [22–25]. The suspension of SeNPs was further centrifuged at 12,000 rpm for 30 min, and the collected precipitate pellet was dried and weighed. The concentration was calculated as follows: 1 mg of SeNPs was dissolved in 1 mL of DMSO, where the final concentration was 1000 µg/mL.
