BIOSYNTHESIS OF SILVER NANOPARTICLES USING LEAF OF Jatropha tanjorensis AND EVALUATION OF THE ANTIBACTERIAL, ANTIOXIDANT AND TOXICITY ACTIVITIES

Abstract

Jatropha tanjorensis is a common weed of field crops with tremendous ethnobotanical importance. Plant-based silver nanoparticles (AgNPs) have been advocated for increased efficiency in drug delivery. This study was designed to synthesise AgNPs from leaves of J. tanjorensis and investigate its antibacterial, antioxidant and toxicity properties. To this end, fresh leaves of the plant were collected, rinsed, dried and pulverised. Proximate and mineral composition of the fresh leaves were determined according to standard protocols. Methanol crude extract (MLE) of the leaf was prepared using methanol as solvent. Three fractions; N-Hexane (HLF), ethyl acetate (ELF) and aqueous (ALF) fractions were then obtained from the MLE. Quantitative and qualitative phytochemical screening and antioxidant potentials of the extracts were determined. Silver nanoparticles were synthesised from all the extracts and characterised. The antibacterial efficacies of the crude methanol leaf extract (MLE) and fractions (HLF, ELF and ALF) and their respective AgNPs solutions were tested against four pathogenic bacteria; Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Streptococcus pyogenes using Agar well diffusion. The Minimum Inhibitory concentration (MIC) and Bactericidal (MBC) concentration were determined. Toxicity evaluations of the most potent AgNP solution were done following standard procedures. Results of proximate analyses revealed that the fresh leaves of J. tanjorensis were richest in Nitrogen Free Extract (NFE) (30.09±1.71 %); and potassium (624.24±9.44 mg/100g) and phosphorus (423.42±6.37 mg/100g). Qualitative and analyses revealed the presence of secondary metabolites, while quantitative analyses showed that cyanide and phytate contents were highest in all the extracts. The quantity of these metabolites were solvent-dependent. Antioxidant analyses showed a dose-dependent scavenging activities against 1,1-diphenyl,1,2 picryhydrazly (DPPH); with MLE being most potent with inhibition concentrations values of 0.425, 0.637 and 0.807 µg/ml for IC50, 75 and 95. Visible colour change indicated the reduction of silver nitrate to its oxide, and formation of AgNPs with absorbance range of 409.40 to 414.60 nm. The AgNPs shows weight loss at temperature of 300 and 480o C in DTA/TGA analyses which suggested that MLE AgNPs solution were heat stable. Nano-sizing revealed AgNPs size ranging from range of 13.86 and 81.11 nm (mean value = 61.79 nm). The antibacterial/ growth inhibitory activities of the extracts were dose-, concentration- and organism-dependent. The activities of the extracts and fractions were enhanced as AgNPs solutions. The MLE AgNPs solution was the most potent and most enhanced of all the AgNPs solution; with zones of inhibition of 21.50±0.71, 43.50±3.54 and 27.00±1.41 mm against S. aureus, S. pyogenes and P. aeruginosa, respectively. Among the organisms, S. pyogenes and P. aeruginosa were most sensitive to all extracts and AgNPs solutions. Acute toxicity studies revealed no mortality at 5000 mg/kgbw. Sub-acute toxicity test revealed that haematological indices and body weights were not significantly (p>0.05) affected by the concentrations tested (150, 300 and 600 mg/kgbw). Organ function tests and histopathological analyses revealed dose dependent toxicity of the extracts on the histology of the liver and kidney. The study revealed enhanced activities of leaf extracts of J. tanjorensis as AgNPs solutions. These AgNPs solutions could, therefore, be good candidates for efficient and effective drug delivery.