Green synthesis of silver nanoparticles using Eulophia herbacea (Lindl.) tuber extract and evaluation of its biological and catalytic activity

The present work is a report on phytosynthesis of silver nanoparticles (AgNPs) carried out using an aqueous extract of the tuber of Eulophia herbacea Lindl. (Orchidaceae) and evaluation of its antimicrobial and catalytic potential. The extract efficiently reduced aqueous silver ions and generated stable and bioactive nanoparticles. The maximum reduction of AgNO3 was achieved when 1 mM AgNO3 was incubated with 2% w/v extract for 5 h. The biosynthesized AgNPs exhibited surface plasma resonance at 447 nm. The zeta potential was -15 mV. Scanning electron microscopy study showed that the average particle size of the AgNPs was 11.70 +/- 2.43 nm and that they were non-agglomerated. An Energy Dispersive X-ray study provided support for the presence of elemental silver. X-ray diffraction studies confirmed that the AgNPs were crystalline and had a face-centered cubic geometry. The AgNPs showed excellent antibacterial and antifungal activity against common human pathogens. This activity was comparable with that of standard antibiotics. The catalytic potential of the AgNPs was studied through the reduction of methylene blue and congo red. The results showed that the AgNPs synthesized using the present method are biologically and catalytically active.