Caesalpinia coriaria leaf extracts mediated biosynthesis of metallic silver nanoparticles and their antibacterial activity against clinically isolated pathogens

• Silver nanoparticles were synthesized using Caesalpinia coriaria aqueous extract.
• Synthesized silver nanoparticles were characterized by UV–vis spectroscopy, SEM, EDX, XRD and FT-IR.
• Antimicrobial activity was evaluated against clinically isolated human pathogens.

A rapid method for synthesis of silver nanoparticles using the leaf extracts of Caesalpinia coriaria that has high level of tannin contents is reported. For leaf extracts preparation, two methods were adopted and compared with their extracellular synthesis of metallic silver nanoparticles. Stable silver nanoparticles produced by treating an aqueous solution of AgNO3 (5 mM) with the leaf extracts as reducing agent of Ag+ to Ag0. The formation of the silver nanoparticles (AgNPs) in the reaction mixture was determined using the surface plasmon resonance band shown in UV–vis spectroscopy. To identify the active biomolecules responsible for the reduction of Ag+ ion and the stabilization of AgNPs synthesized the functional group available in C. coriaria leaf extracts (CCLE) was studied by Fourier transmission infrared (FT-IR) spectroscopy. The X-ray diffraction (XRD) analysis showed the crystalline structure of metallic silver ions. The energy dispersive X-ray spectroscopy (EDX) analysis of AgNPs was confirmed the presence of pure elemental silver ion with no other impurity peaks. The morphology and topography of the AgNPs were determined using field emission scanning electron microscopy (FESEM). The size of the silver nanoparticles was differed by the kind of leaf extracts used for synthesis. The morphology of the AgNPs synthesized using boiled leaf extracts was found to be triangle shape with diameter range from 40 nm to 52 nm whereas in the case centrifuged leaf extracts, three shapes viz., triangle, hexagonal and spherical were noticed with an average size between 78 nm and 98 nm. Furthermore the synthesized AgNPs were found to show potential antimicrobial activity against multidrug resistant Gram-positive (Escherichia coli and Pseudomonas aeruginosa) and Gram-negative (Klebsiella pneumoniae, and Staphylococcus aureus) clinically isolated human pathogens. The present results clearly indicated that the CCLE is a good nontoxic source for extracellular synthesis of AgNPs in eco-friendly way as compared to other methods. Thus C. coriaria leaf extracts provide a potential source for development of commercially important industrial products including cosmetics and nanomedicines by tagging nanoparticels with tannins in the future.