Silver nanoparticles from leafy green extract of Belgian endive (Cichorium intybus L. var. sativus): Biosynthesis, characterization, and antibacterial activity

•First report on the synthesis of AgNPs using leafy green extract of Belgian endive.•Biosynthesized AgNPs were characterized with UV–vis, TEM, XRD, and SERS.•Biosynthesized AgNPs showed antibacterial effect at picomolar concentration levels. [Display omitted] We report for the first time a green, simple, and low-cost synthesis of silver nanoparticles (AgNPs) by mixing AgNO3 solution with the aqueous leaf extract of Belgian endive, a variety of Cichorium intybus L., without any harmful reducing and capping agents. The biosynthesis of AgNPs was observed by the color charge from colorless (metal salt solution) to a yellowish brown (nanoparticle colloidal dispersion), which was confirmed by UV–vis spectroscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD). UV–vis spectra showed the surface plasmon resonance signature of AgNPs around 420nm, TEM revealed that nanoparticles were quasi-spherical with an average diameter ranging from 19 to 64nm depending on the metal salt concentration, and XRD pattern indicated that the biosynthetic process produced face-centered cubic AgNPs. Surface-enhanced Raman spectroscopy analysis showed that the AgNPs were capped with bioactive molecules from the leaf extract, which are also believed to be responsible for the bio-reduction of silver ions. The antibacterial activity of the biosynthesized AgNPs was studied using both the disk diffusion and minimum inhibitory concentration methods against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa, and they were found to be effective at picomolar concentration levels.