Biosynthesizing of silver nanoparticles using microorganisms or various plant parts have proven more environmental friendly, cost-effective, energy saving and reproducible when compared to chemical and physical methods. This investigation demonstrated the plant-mediated synthesis of silver nanoparticles using the aqueous leaf extract of Thevetia peruviana. UV–Visible spectrophotometer was used to measure the surface plasmon resonance of the nanoparticles at 460 nm. Fourier Transform Infrared showed that the glycosidic –OH and carbonyl functional group present in extract were responsible for the reduction and stabilization of the silver nanoparticles. X ray diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy and Selected Area Electron Diffraction analyses were used to confirm the nature, morphology and shape of the nanoparticles. The silver nanoparticles are spherical in shape with average size of 18.1 nm. The synthesized silver nanoparticles showed activity against fungal pathogens and bacteria. The zone of inhibition observed in the antimicrobial study ranged between 10 and 20 mm.

Biosynthesized silver nanoparticles (AgNPs) usingCassia hirsutaaqueous leaf extract were reported in this study. The synthesis was optimized by measuring various parameters such as temperature, time, volume ratio, and concentration. The surface plasmon resonance at 440 nm for 30°C and 420 nm for both 50°C and 70°C measured using the UV-Vis spectrophotometer confirmed the formation of AgNPs synthesized usingC.hirsuta(CAgNPs). The functional groups responsible for the reduction and stabilization of the NPs were identified using Fourier Transform Infrared (FTIR). The morphology, size, and elemental composition of the NPs were obtained using scanning electron microscope (SEM), transmission electron microscope (TEM), and energy dispersive X-ray spectroscopy (EDX). X-ray diffractometer was used to identify the phases and crystallinity of CAgNPs. Crystalline spherical NPs with average diameter of 6.9 ± 0.1 nm were successfully synthesized. The thermal analysis of CAgNPs was observed from DSC-TGA. The larvicidal results against the different larva instar stage ofCulex quinquefasciatusgave LC₅₀= 4.43 ppm and LC₉₀= 8.37 ppm. This is the first study on the synthesis of AgNPs usingC.hirsutaand its application against lymphatic filariasis vector. Hence, it is suggested that theC.hirsutasynthesized AgNPs would be environmentally benign in biological control of mosquito.

Native South Africans make use of Helichrysum aureonitens Sch. Bip. extracts for the treatment of a variety of infections and they are important in traditional medicinal preparations. This study investigated the effect of seasonal variation and geographical location on the antibacterial and antifungal activities of H. aureonitens. Material was collected in two different seasons: early spring, with high rainfall and high temperatures (October), and late autumn, with low rainfall and lower temperatures (May). Further analysis was carried out using ¹H-NMR based metabolomics to analyse and compare the chemical profiles of the plants in both seasons and locations. Plant materials were collected from two sites for each season, at Wakefield farm (KwaZulu-Natal), representing a colder, wetter environment, and Telperion (Mpumalanga), representing a drier and warmer environment. Leaves of H. aureonitens were tested against bacteria (Proteus vulgaris (P. vulgaris) and Bacillus subtilis (B. subtilis)) as well as fungi (Aspergillus flavus (A. flavus), Aspergillus nomius (A. nomius), Cladosporium cladosporioides (C. cladosporioides), Fusarium oxysporum (F. oxysporum) and Penicillum halotolerans (P. halotolerans)). Extracts from the October harvest showed significant activities against the Gram-negative bacterium P. vulgaris compared to the May harvest, with an MIC value of 62.5 µg/mL. Similar activity was observed between the extracts from the wet season across the two geographically different locations. There was generally very good antifungal activity observed for all the species, with the exception of A. nomius, which had MIC values ranging from 0.39–1.56 µg/mL. Extracts of plant materials harvested in the wetter region had a significantly higher activity against A. flavus and F. oxysporum in both seasons than those from plants harvested in the drier region. Telperion-harvested plants exhibited better activity against F. oxysporum in the autumn. Hydrogen-1 NMR metabolomic analysis confirmed the significant effects of the seasons and the peculiar climates of different localities on the secondary metabolite profile of H. aureonitens.