The effect of silver nitrate concentration on biological synthesis of silver nanoparticles by aspergillus niger and the evaluation of its antibacterial properties

Abstract

Recently, biosynthesis of nanoparticles has attracted scientist’s attention due to its costeffective production and less toxic wastes during the process of synthesis compared to chemical and physical methods. Moreover, many studies have reported that biosynthesized nanoparticles, especially silver nanoparticles (AgNPs), demonstrated a broad-spectrum antibacterial activity. Therefore, this synthesis method could be a good alternative way to develop environmentalfriendly nanotechnology. In this study we investigated the biosynthesis of AgNPs using cell free extract (CFE) from Aspergillus niger and enhanced the product yields by the optimization of silver nitrate (AgNO₃) concentrations. These AgNPs were characterized through UV-visible spectrophotometry, transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurement. The 5-80 nm of spherical AgNPs were visualized using TEM. A peak at 420 nm was observed by UV-visible spectrophotometry, and the result showed that the maximum synthesis of AgNPs was obtained at 2 mM of AgNO₃ concentration under the condition parameters of 30°C incubation temperature at pH of 7 and the use of 25 grams of fungal biomass. The antibacterial activities of the AgNPs were investigated against Grampositive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli) by determination of inhibition zones using agar-well diffusion method. The various doses of AgNPs (1000, 500 and 250 μg/mL) exhibited antibacterial activity; the inhibition zones of S. aureus were in the range of 9.3-12.7 mm, whereas E. coli showed unclear inhibition zones. To sum up, our study demonstrated a successful biosynthesis method of AgNPs using A. niger and the application of this nanomaterial as an antibacterial agent.