Biogenically Synthesized Silver/Gold Nanoparticles, Mechanism and their Applications: A Review

Green nanoparticle synthesis is a vital branch in nanotechnology. These nanoparticles are synthesized with the aid of phytochemicals in plant extracts. The phytochemicals also stabilize the synthesised nanoparticles eliminating the use of toxic capping agents. Silver and gold (Ag NPs, Au NPs) green nanoparticles are common. They have wide applications in areas such as diagnosis, drug delivery and therapeutics. Despite their great applications, particle agglomeration greatly hinders their usage. As such, we explore various synthetic methods used to obtain green nanoparticles. Reaction mechanisms of the phytochemicals and precursor metals used to obtain the nanoparticles are studied in detail so as to get to the core of the problem. Use of broths obtained by boiling fresh plant leaves, stem, roots, bark or peels of fruits is the most widely used synthetic pathway. Reaction temperature, pH and metal concentration are the crucial factors controlling agglomeration and particle size. Furthermore, incorporation of sunlight in the synthetic pathway was found to be economically important. The functionality of the as-synthesized nanoparticles can be modified through careful selection of the plant material used. Specifically, use of ethnomedical plants such as Azadirachta indica leaves and Hibiscus rosa-sinensis among others is documented to produce nanoparticles with therapeutic functions. It is desirable to obtain small size non-agglomerated green nanoparticles as the size of the nanoparticles affects their antimicrobial activity. In addition, smaller nanoparticles are more effective in drug delivery.