UV-visible spectra of (A) aqueous suspension of Ag-SiO2 NPs at 1000, 100, 10, 1, and 0.1 μg/mL (top to bottom) and (B) aqueous solution of Ag-c NPs at 85, 42.5, 8.5, 0.85, 8.5 × 10−2, and 8.5 × 10−3 μg/mL (top to bottom). (C, D) Antibacterial effect in culture tube after 24 hours’ incubation of (C) Ag-SiO2 NPs (lefthand tube contains 100 μg/mL Ag-SiO2 NPs and E. coli, and righthand tube contains only E. coli control); (D) Ag-c NPs (lefthand tube contains 42.5 μg/mL Ag-c NPs with E. coli, and righthand tube contains only E. coli control). (E, F) Growth test of E. coli on agar plates. (E) Lefthand plate contains Ag-SiO2 NPs + E. coli, and righthand plate contains only E. coli control, which contains ~1.78 × 106 cfu of E. coli. (F) Lefthand plate contains Ag-c NPs + E. coli, and righthand plate contains only E. coli control, which contains ~1.28 × 106 cfu of E. coli.