Abstract
We report here biosynthesis of silver nanoparticles (AgNPs) using aqueous extracts of (i) Azadirachta indica leaves and (ii) Citrullus colocynthis fruit and their larvicidal activity against Aedes aegypti. The UV–Vis spectroscopy absorption peaks occurred in the range of 412–416 nm for A. indica AgNPs and 416–431 nm for C. colocynthis AgNPs indicating the silver nature of prepared colloidal samples. The scanning electron microscopy examination revealed the spherical morphology of both types of NPs with average size of 17 ± 4 nm (A. indica AgNPs) and 26 ± 5 nm (C. colocynthis AgNPs). The X-ray diffraction pattern confirmed the face-centred cubic (FCC) structure with crystallite size of 11 ± 1 nm (A. indica AgNPs) and 15 ± 1 nm (C. colocynthis AgNPs) while characteristic peaks appearing in Fourier transform infrared spectroscopy analysis indicated the attachment of different biomolecules on AgNPs. The larvicidal activity at different concentrations of synthesized AgNPs (1–20 mg l−1) and extracts (0.5–1.5%) against Aedes aegypti was examined for 24 h. A concentration-dependent larvicidal potential of both types of AgNPs was observed. The LC50 values were found to be 0.3 and 1.25 mg l−1 for C. colocynthis AgNPs and A. indica AgNPs, respectively. However, both extracts did not exhibit any notable larvicidal activity.
Highlights
Nanotechnology, owing to unique, extraordinary and incredible properties of materials at nanoscale, has revolutionized almost every field of science and technology
Addition of extract induces the reduction of these Ag-ions to free Ag-atoms (Ag0) by gaining the electrons. This reduction can be termed bio-reduction or plant-assisted reduction, because it is caused by different biomolecules such as protein and phytochemicals present in the extract which serve as reducing agent [25]
The colour of the reaction solution may change from transparent to light yellow to yellowish brown and dark brown depending upon the type of the extract used. This timedependent colour change during the synthesis (10 min for A. indica AgNPs and 20 min for C. colocynthis AgNPs), indicates the different phases of nucleation and growth process occurring in the reactions [26]
Summary
Nanotechnology, owing to unique, extraordinary and incredible properties of materials at nanoscale, has revolutionized almost every field of science and technology. We chose Azadirachta indica and Citrullus colocynthis for the synthesis of AgNPs, because both of these plants are famous for good medicinal properties and exhibit effective biological activities. The C. colocynthis fruit contains many biomolecules including alkaloids, glycosides, flavonoids and fatty acids which are famous for important biological activities, such as anti-microbial, anti-oxidants, cytotoxic, anti-diabetic, anti-lipidemic and insecticidal [12] That is why it is considered one of the best medicinal plants and is used in different biomedical applications including anti-microbial, anticancer activities [12,13,14]. Inhibiting larvae in water by conventional ways using pesticides can increase the toxic risks for environment and humans Natural pesticides such as plant extracts can be simple and side effect-free promising methodologies. A. indica and C. colocynthis-mediated AgNPs were synthesized, characterized and tested for their larvicidal activity against A. aegypti and it was found that these AgNPs can potentially be considered good anti-larvicidal agents
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