Physicochemical Parameters and Antibacterial Activity of Biosynthesized Silver Nanoparticles from Carica papaya Leaf Extract

Abstract

In this research work, Silver nanoparticles were synthesized from Carica papaya leaf extract via green route. The physicochemical parameters including boiling point, color, odor, density, pH as well as the solubility of papaya leaf extract were first determined before proceeding with the synthesis of silver nanoparticles. The formation of Silver Nanoparticles first, was identified by color change from light brown to dark brown after the nucleation of the metal ions indicating that phytoconstituents of Carica papaya resulted in the reduction of Ag+ to Ag0, a phenomenon that could be attributed to the surface Plasmon absorption. The bio fabricated silver nanoparticles were characterized using UV – Visible and SEM to be certain of its formation before being deployed in the antibacterial studies. The UV-Vis spectral analysis showed maximum absorbance of 1.05 at a corresponding wavelength (λ max) of 400nm reflecting the surface Plasmon resonance of silver NPs from papaya leaves which is characteristic of Silver Nanoparticles. SEM image revealed that, the synthesized silver nanoparticles have a spinel like structure and an average size of about 50nm. The antibacterial studies of Silver nanoparticles were conducted against B. subtilis, K. pneunoniae, P. aeruginosa, E. coli, and S. typhi. Different concentrations of 100, 200, 300, 400 and 500μg/L of Silver nanoparticles were tested against each pathogen. The inhibition zone increases generally with increase in concentrations of silver nanoparticles. At higher concentration of 500μg/L, the zones of inhibition were in the following order; 24.44mm, 17.64mm, 17.52mm, 16.88mm, and 16.00mm for B. subtilis, P. aeruginosa, E. coli, K. pneumoniae and S. typhi respectively. The zone of inhibition for Augmentin was found to be higher compared to silver nanoparticles for each pathogen, except for P. aeruginosa where it is almost the same, an indication of high activity of silver nanoparticles against P. aeruginosa due to the comparability with Augmentin. For each concentration investigated, B. subtilis demonstrated higher zone of inhibition as compared to other pathogens studied in this work, hence, Ag NPs may be a potential antibiotic.