Silver nanoparticles: green synthesis using Phoenix dactylifera fruit extract, characterization, and anti-oxidant and anti-microbial activities

Abstract

Hydro-alcoholic (2:8 v/v) extract of the pulp of Phoenix dactylifera fruit pulp obtained using Soxhlet extraction (70 °C, 6 h) was found to contain alkaloids, sterols, tannins, flavonoids, cardiac glycosides, proteins, and carbohydrates. An aqueous solution (20% v/v) of the extract led to the synthesis of silver nanoparticles (AgNPs) from 0.01 M AgNO₃ solution as confirmed by the surface plasmon resonance at 445 nm determined using UV–visible spectroscopy after 24 h. The synthesized AgNPs were found to be mostly spherical and complexed with phytochemicals from the extract. The size of AgNPs ranged from 12.2–140.2 nm with mean diameter of 47.0 nm as characterized by scanning electron microscopy (SEM). The elemental composition of the AgNPs complexed with the phytochemicals was found to be 80.49% silver (Ag), 15.21% carbon (C), and 4.30% oxygen (O) on a weight basis by energy-dispersive spectroscopy (EDS). Using the α,α-diphenyl-β-picrylhydrazyl (DPPH) assay, an anti-oxidant activity of 89.15% for 1 µg L⁻¹ ultrasonically homogenized ethanolic solution of complexed AgNPs was obtained (equivalent to 0.20 mg mL⁻¹ gallic acid solution), while methanolic solution of plant extract possessed an EC₅₀ value of 3.45% (v/v) (equivalent to 0.11 mg mL⁻¹ gallic acid solution). The plant-nanosilver broth was also found to possess effective anti-microbial activity against Escherichia coli ATCC 8739, Staphylococcus aureus ATCC 6538, and Candida albicans ATCC 10231 as assessed by the disc diffusion assay. However, the plant extract showed negligible anti-microbial activity.