Optimised microwave-assisted biosynthesis of silver nanoparticles from Nothapodytes foetida leaf extracts and its anti-microbial activities

Abstract

The present investigation reports the biogenesis of silver nanoparticles (Ag NPs) using extracts of a medicinal plant Nothapodytes foetida. Total phenolic content (TPC) and ferric reducing antioxidant power (FRAP) assay were carried out for the microwave-assisted extract (MAE) of N. foetida using methanol as solvent and the conditions for extraction were optimised by response surface methodology (RSM). The effects of operating variables such as extraction time, temperature and ratio of sample to solvent were studied using central composite design (CCD). A mathematical model with a high determination coefficient (R2) for TPC (0.991) and FRAP (0.995) was obtained. The optimal conditions of extraction for TPC were 48.6 ºC, 23.15 min and 2.04:30 (g/mL) and for FRAP 52.31ºC, 12.32 min and 1.67: 30 (g/mL). Under these conditions, the experimental yields of TPC and FRAP were 2.426 mg gallic acid equivalents (GAE)/g dry powder and 14.985mg of FeSO4·7H2O/g of dry powder, respectively. Ag NPs were characterised using UV–Vis spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The synthesised Ag NPs have also shown potent activity against the human pathogenic Staphylococcus aureus.