Fig. 9. Images of comparative antibacterial studies of different nanoparticles SiO₂, SiO₂@Au, SiO₂@Ag and SiO₂@Au–Ag at different concentration 50 μg mL⁻¹, 100 μg mL⁻¹, 150 μg mL⁻¹, 200 μg mL⁻¹ against bacteria E. coli and S. aureus with respect to positive control of ampicillin (200 μg mL⁻¹).