Synthesis of metallic and semiconductor nanoparticles through physical and chemical routes has been extensively reported. However, green synthesized metal nanoparticles are currently in the limelight due to the simplicity, cost-effectiveness and eco-friendliness of their synthesis. This study explored the use of aqueous leaf extract of Costus afer in the synthesis of silver nanoparticles (CA-AgNPs). The optical and structural properties of the resulting silver nanoparticles were studied using UV-visible spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infra–red spectrophotometer (FTIR). TEM images of the silver nanoparticles confirmed the existence of monodispersed spherical nanoparticles with a mean size of 20 nm. The FTIR spectra affirmed the presence of phytochemicals from the Costus afer leaf extract on the surface of the silver nanoparticles. The electrochemical characterization of a CA-AgNPs/multiwalled carbon nanotubes (MWCNT)-modified electrode was carried out to confirm the charge transfer properties of the nanocomposites. The comparative study showed that the CA-AgNPs/MWCNT-modified electrode demonstrated faster charge transport behaviour. The anodic current density of the electrodes in Fe(CN)6]4−/[Fe(CN)6]3− redox probe follows the order: GCE/CA-Ag/MWCNT (550 mA/cm2) > GCE/MWCNT (270 mA/cm2) > GCE (80 mA/cm2) > GCE/CA-Ag (7.93 mA/cm2). The silver nanoparticles were evaluated for their antibacterial properties against Gram negative (Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa) and Gram positive (Bacillus subtilis and Staphylococcus aureus) pathogens. The nanoparticles exhibited better inhibition of the bacterial strains compared to the precursors (leaf extract of Costus afer and silver nitrate). Furthermore, the ability of the nanoparticles to scavenge DPPH radicals at different concentrations was studied using the DPPH radical scavenging assay and compared to that of the leaf extract and ascorbic acid. The nanoparticles were better DPPH scavengers compared to the leaf extract and their antioxidant properties compared favorably the antioxidant results of ascorbic acid. The green approach to nanoparticles synthesis carried out in this research work is simple, non-polluting, inexpensive and non-hazardous.

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A simple and cost-effective material composed of polyacrylonitrile nanofibers containing different concentrations of moringa (MR) leaf extracts was fabricated for antimicrobial properties and wound dressing. The fabricated materials were characterized by scanning electron microscopy, thermal gravimetric analysis, and Fourier transmission infrared spectroscopy. The antibacterial sensitivity of the developed polyacrylonitrile-moringa extract nanofibers was evaluated against Staphylococcus aureus and Escherichia coli by the agar diffusion method. A pronounced antibacterial activity was observed with the increase in the incorporated moringa leaf extract concentration within the polyacrylonitrile-moringa extract nanofibers against the bacterial strains. The best antibacterial sensitivity was observed for nanofibers containing 0.5 g of moringa leaf extract which had an inhibitory zone of 15 mm for E. coli and 12 mm for S. aureus. Furthermore, the cost-effective and biodegradable nanofibrous polyacrylonitrile–moringa extract nanofiber was also used to conduct further studies regarding wound dressing. The result reveals that the increase in the concentrations of moringa leaf extract influenced the healing properties of the material. For days 1, 4, and 7 of the wound dressing experiment, the % wound closure of the rat was the highest for the nanofiber containing 0.5 g of moringa leaf extract (35, 87, and 95%, respectively) compared to the positive control medical gauze (29, 75, and 93%, respectively).

The health challenges associated with pathogens and ectoparasites highlight the need for effective control approaches. Metal nanoparticles have been proposed as highly effective tools towards combatting different microbial organisms and parasites. The present work reports the antimicrobial and larvicidal potential of biosynthesized Ag/Ag2O nanoparticles using aqueous leaf extract of Eupatorium odoratum (EO). The constituents of the leaf extract act as both reducing and stabilizing agents. The UV-VIS spectra of the nanoparticles showed surface plasmon resonance. The particle size and shape of the nanoparticles was analysed by transmission electron microscopy (TEM). The larvicidal study was carried out using third and fourth instar Culex quinquefasciatus larvae. The mosquito larvae were exposed to varying concentrations of plant extract (EO) and the synthesized nanoparticles, and their percentage of mortality was accounted for at different time intervals of 12 h and 24 h periods of exposure. The nanoparticles were more lethal against third and fourth instars of Culex quinquefasciatus larvae at the 24 h period of exposure with lower lethal concentration values (LC50 = 95.9 ppm; LC90 = 337.5 ppm) and (LC50 = 166.4 ppm; LC90 = 438.7 ppm) compared to the plant extract (LC50 = 396.8 ppm; LC90 = 716.8 ppm and LC50 = 448.3 ppm; LC90 = 803.9 ppm, respectively). The antimicrobial properties of the nanoparticles were established against different clinically-isolated microbial strains and compared to that of the plant extract (EO) and standard antimicrobial drugs. The nanoparticles were generally more active than the plant extract against the selected microbial organisms. The Gram-negative bacterial strains Escheerichua coli and Salmonella typhi were more susceptible towards the nanoparticles compared to the Gram-positive strains and the fungal organism.

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