Green synthesis of silver nanoparticles using aqueous leaf extract of Premna integrifolia (L.) rich in polyphenols and evaluation of their antioxidant, antibacterial and cytotoxic activity

Abstract

Premna integrifolia L. is widely distributed in tropical and subtropical regions. In the present study, green silver nanoparticles were synthesized efficiently after mixing 1 mmol/L AgNO3 and 4% aqueous leaf extract at neutral pH (7.0) after 25 min sunlight exposure. The aqueous leaf extract was enriched with polyphenols. It had higher flavonoid (67.23 ± 1.23 µg/mg gallic acid equivalent) than phenolic content (58.10 ± 2.29 µg/mg rutin equivalent). The bio-synthesized silver nanoparticles were characterized by different spectroscopic and microscopic studies. The synthesized nanoparticles were spherical in shape and ranged from 9 to 35 nm in size. The crystalline nature of the nanoparticles was confirmed on the basis of high-resolution transmission electron microscopy (HRTEM), high-resolution scanning electron microscopy (HRSEM), X-ray diffractometry (XRD) and selected area electron diffraction (SAED) analyses. The presence of silver ions in the biosynthesized nanoparticles was demonstrated based on energy-dispersive X-ray (EDX) data (3.5 keV). The functional groups involved in the nanoparticle synthesis were analysed using FT-IR. These silver nanoparticles showed good antibacterial activity against human pathogenic gram-positive (Staphylococcus aureus, Enterococcus faecalis) and gram-negative (Shigella dysenteriae, Shigella flexneri and Vibrio parahaemolyticus) bacteria. The silver nanoparticles exhibited good in vitro antioxidant and cytotoxic activity to human cervical cancer cell line (SiHa).