One-pot synthesis of silver nanocomposites from Achyranthes aspera: An eco-friendly larvicide against Aedes aegypti L.

Abstract

Objective: To formulate silver nanocomposites from Achyranthes aspera leaf extracts and evaluate its larvicidal activity against Aedes aegypti. Methods: The silver nanocomposites were synthesized from Achyranthes aspera leaf extracts. The process was optimized and traced through UV-visible and photon correlation spectroscopy. The larvicidal potential of silver nanocomposites of Achyranthes aspera leaf extracts was assessed against the early fourth instars of Aedes aegypti and three non-target organisms. Furthermore, the most effective and eco-safe nanocomposite was characterized by different biophysical techniques including scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform-infrared spectroscopy (FT-IR). Results: The formulated silver nanocomposites exhibited efficient larvicidal efficacy against Aedes aegypti. Bioassay with silver nanocomposites formulated using different AgNO 3 concentrations (3, 4, and 5 mM) revealed respective LC50 values of 37.570, 6.262 and 1.041 μg/mL; 5.819, 1.412 and 0.489 μg/mL; and 5.519, 1.302 and 0.267 μg/mL after 24, 48 and 72 h. The silver nanocomposites with 4 mM AgNO3 were selected for characterization. SEM and TEM analysis revealed spherical, poly-dispersed structure with varied diameters of 1-25 nm. The XRD analysis established the crystalline and face-centred-cubic structure of silver nanocomposites with the maximum peak at a 2θ value of 37.42°. The EDX pattern showed the presence of Ag, O and C in the nanocomposites in their order of weight%. The FT-IR displayed visibly distinct peaks in different ranges demonstrating the intricacy of silver nanocomposites. In addition, the lethal concentrations of silver nanocomposites of Achyranthes aspera leaf extracts against Aedes aegypti larvae were non-toxic to non-target organisms including Gambusia affinis, Daphnia magna and Moina macrocopa. Conclusions: Silver nanocomposites synthesized with leaf extract of Achyranthes aspera provide a cost-effective and eco-safe alternative to conventional insecticides, and can be utilized as a potent mosquito nano-larvicide.

Keywords

• achyranthes aspera; aedes aegypti; larvicidal; silver nanocomposites; sem-tem; edx; xrd; ft-ir