Size-tunable Sargassum polycystum mediated synthesis of silver nanoparticles and its larvicidal effect on Aedes aegypti

One-pot green synthesis of silver nanoparticles (AgNPs) utilising marine brown seaweed ( Sargassum polycystum ) extract was developed. In this study, the size profile of the silver nanoparticles produced is investigated and it is found to be tunable by varying the synthesis parameters such as concentration of seaweed extract, concentration of silver nitrate, temperature, and pH. Various instrumentation and techniques such as Ultraviolet–Visible (UV–Vis) spectroscopy, dynamic light scattering (DLS), x-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDX), Fourier-transformed infrared spectroscopy (FT-IR) and high resolution transmission electron microscope (HR-TEM) were used to characterise the AgNPs. The findings shows that varying pH, temperature, and silver nitrate (AgNO 3 ) concentration in the reaction resulted AgNPs with different sizes. While controlling the ratio between the AgNO 3 and seaweed concentration greatly affects the polydispersity index (PDI) of the produced AgNPs. In this study, small size AgNPs with 0.72 ± 0.02 nm and PDI 0.581 ± 0.014 as detected by DLS analysis can be produced under reaction conditions of pH 11 and 85 °C. Besides that, the larvicidal potential of AgNPs was studied against Instar III Aedes agypti larvae with a tested concentration range of 20–100 ppm. The LC 50 against A. aegypti larvae were found to be 103.10 ppm at 24 h and 46.67 ppm at 48 h. In addition, the synthesised AgNPs exhibit very low toxicity against non-target species Artemia salina. The outcome of this study has provided insights towards the significance of tuning various synthesis conditions to produce small sized and improved polydispersity of the AgNPs. The study has also revealed the potential use of the seaweed mediated synthesized AgNPs to control Aedes mosquito larvae population whilst not harming the non-target species such as brine shrimp, Artemia salina.