A comparative analysis of capping and reducing agents of microbial cell Aspergillus niger and Bacillus subtilis for biosynthesis of Ag doped ZnO nanoparticles

In this study, green synthesis of Ag doped ZnO (AZNPR) has been carried out using the sol-gel method at pH 8.0, using two types of microbial cells, namely Aspergillus niger and Bacillus subtilis as capping and reducing agents. This work centred on the phytomediated biosynthesis and characterisation of AZNPR and its biological utility. Based on infrared analysis, phytochemicals present in microbial cells are extracellular enzymes namely proteolytic, amylolytic, lipolytic, cellulolytic, and pectinase, which can be extracted from A. niger and B. subtilis and are responsible for controlling the growth of AZNPR. The formation of AZNPR was characterised using different analyses. The FTIR shows absorption band located at ∼864 cm⁻¹ that shows the interaction between Ag and ZnO. The XRD results showed the presence of crystalline AZNPR in the forms of hexagonal wurtzite ZnO and Ag. Microstructural and size examination showed that AZNPR was in the form of nanorods with homogeneous distribution with a size of rods in A. niger media 137.0 nm, while in B. subtilis media 197.4 nm. The Ag–ZnO nanorods revealed the ability to inhibit Candida albicans species, a fungus causing infectious disease, with an inhibition zone measuring 2.1–3.2 mm at 24 h.