Green biosynthesis of single and bimetallic nanoparticles of iron and manganese using bacterial auxin complex to act as plant bio-fertilizer

Iron and manganese nanoparticles (NPs) were synthesized through a simple and rapid method using bacteria supernatant containing auxin complex (indole-3-acetic, IAA) and evaluated as plant nanofertilizer. Successful biosynthesis of FeOx NPs and MnOx NPs, and bimetallic MnOx/FeOx NPs were demonstrated through transmission electron microscopy (TEM), which showed the presence of spherical agglomerated NPs, and UV-visible spectroscopy, which confirmed an absorbance peak around 250-300 nm. Fourier Transform Infrared spectrometer (FTIR) revealed correspondent bands of auxin at the synthesized NPs confirming that the auxin complex acted as reductive/capping agent. In general, bimetallic MnOx/FeOx NPs from bacterial supernatant showed best result on plant growth, especially in germination rates, root growth and fresh weight in maize plantlets, and thus can be used as micronutrient nanofertilizer.