Green synthesis of gold nanoparticles using neem seed extract: Antioxidant, antimicrobial, and catalytic properties

Gold nanoparticles are one of the most distinguished nanoscale metallic materials that have garnered more attention among the various noble metallic nanoparticles with potential applications in catalysis, biotechnology, pharmacology, medical imaging, optics, etc., because of their low toxicity, biocompatibility, and high surface to volume ratio that can be functionalised with various ligands. Due to the their medicinal, biological and economic importance, Azadirachta indica A. Juss. seeds were selected for the biosynthesis of gold nanoparticles (AuNPs) due to their low cost, one step, eco-friendly and no need for reducing and stabilizing agents. Optimization of various parameters was performed during the biosynthesis of gold nanoparticles, which influenced the size and morphology of the synthesized nanoparticles (NPs). AuNPs' surface plasmon resonance (SPR) was detected between 530 and 550 nm. Characterization of the biosynthesized NPs was performed by using different techniques. Under optimal conditions, the size of the nanoparticles was found to be between 10 and 25 nm. An aqueous extract of the seeds was compared to the antioxidant and antimicrobial (antibacterial and antifungal) properties of gold nanoparticles. The efficient catalytic activity of AuNPs was observed in the first order reduction reaction of 4-nitrophenol to 4-aminophenol with a rate constant of 0.103 min-1. The results showed that an efficient, low-cost green method for the biosynthesis of AuNPs using A. indica seed aqueous extract, with significant biological and catalytic properties.