Abstract
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.
Highlights
Nanoparticles with controlled size, shape and structure are important building blocks for many optical, magnetic, electronic, and biomedical applications [1]
Metal nanoparticles exhibit phenomena when when metal electrons in the conduction band collectively oscillate in resonance with certain wavelengths of metal electrons in the conduction band collectively oscillate in resonance with certain wavelengths incident light
The significance values obtained from one way analysis of variance (ANOVA) were below 0.05; there were significant differences in the different means
Summary
Nanoparticles with controlled size, shape and structure are important building blocks for many optical, magnetic, electronic, and biomedical applications [1]. The synthesis of silver nanoparticles can be achieved by using various methods which involve chemical reduction [5], photochemical reduction [6], electrochemical reduction [7], and heat vaporization [8]. These processes all involve different toxic chemicals as reducing agents or stabilization agents for the silver ion. In order to circumvent the complication of toxicity in the synthesis of silver nanoparticles due to their potential biological applications, plants or plant extracts have been established to have a leading role in the. Phytosynthesis (the use of plant extracts in synthesis of nanoparticles) of metal nanoparticles incorporates the use of weed, seeds, gums, fruits, roots, bark, sap and flowers [9]
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