Cola nitida-Mediated Biogenic Synthesis of Silver Nanoparticles Using Seed and Seed Shell Extracts and Evaluation of Antibacterial Activities

Abstract

In this study, seed and seed shell extracts of Cola nitida were investigated for the biogenic synthesis of silver nanoparticles (AgNPs) under ambient condition. The biosynthesized AgNPs were characterized through visual development of colour, UV–vis spectroscopy, Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The antibacterial activities of the AgNPs were determined using some multidrug-resistant clinical isolates. The biosynthesized AgNPs depicted brown and yellowish orange colour using seed and seed extract, respectively, with maximum absorbance readings at 457.5 and 454.5 nm. The FTIR spectrum showed strong peaks at 3292.49, 2086.98 and 1631.78 cm−1 for seed extract-mediated AgNPs, while peaks of 3302.13, 2086.05 and 1633.71 cm−1 were obtained for seed shell extract-mediated AgNPs, all indicating that proteins were the capping and stabilization molecules in the biogenic synthesis of AgNPs. The AgNPs were spherical in shape with sizes ranging from 8 to 50 and 5 to 40 nm for seed and seed shell-mediated AgNPs, respectively. The energy-dispersive X-ray (EDX) analysis showed the presence of silver as a prominent metal, while the selected area electron diffraction (SAED) pattern conformed to the face-centred cubic phase and crystalline nature of AgNPs. At various concentrations ranging from 50–150 μg/ml, the AgNPs inhibited growth of multidrug-resistant strains of Klebsiella granulomatis, Pseudomonas aeruginosa and Escherichia coli to the tune of 10–32 mm. Comparatively, seed shell extract-mediated AgNPs had better activities with minimum inhibitory concentration (MIC) of 50 μg/ml against all the tested isolates, while the MICs of seed extract-mediated AgNPs were obtained as 50, 80 and 120 μg/ml against E. coli, P. aeruginosa (wound) and P. aeruginosa (burn), respectively. This study has demonstrated the feasibility of eco-friendly biogenic synthesis of AgNPs using seed and seed shell extracts of C. nitida, and the report to the best of our knowledge is the first reference to extracts of C. nitida for the green synthesis of AgNPs.