A critical review on quantitative growth evolution of biomediated gold and silver nanostructures

Phytosynthesis of metallic nanoparticles has attracted significant interest due to its unique and advantageous features, such as cost-effectiveness, one step fabrication approach, ecofriendly and reliance on renewable resources. However, quantitative growth evolution of phytomediated gold and silver nanostructures is relatively scarce and little explored, despite the strong correlation of surface characteristics with their exponentially growing potential medical and industrial applications. Therefore, it becomes highly needful to thoroughly understand the quantitative growth dynamics of plants-mediated gold (AuNPs) and silver nanoparticles (AgNPs) for achieving their tuneable surface features, which may ultimately play a vital role in enhancing their efficacy for drug delivery, catalysis, and antibacterial functions. In this context, current review aims to elucidate the growth behaviour of biofabricated AuNPs and AgNPs, emphasizing the need for a clear mechanistic structural understanding. Such insights are expected in enabling, phytofabrication of nanoparticles with controllable surface properties, thereby improving their functional performances. This review has elucidated the key mechanisms, involved in formation and size enlargement of AuNPs and AgNPs, comprising of nucleation and growth, directed by oxidized biomolecules. The evolution of the growth stage, known as the dominant rate-determining step in particle size development, is critically analyzed, alongside subsequent processes of diffusion and surface adsorption, collectively governing the nanostructure formation. The involvement of phytochemicals in directing the surface characteristics of nanoparticle during the early phase of synthesis is discussed, with a particular focus on their encapsulating influence on surface adsorption and diffusion inhibition, represented by Orientation Attachment (OA) mechanism. Furthermore, the late-stage evolution of nanoparticle is also conclusively explained, highlighting the diffusion-controlled growth, led by desorption or poor biostabilization of biocompounds, as governed by the Ostwald Ripening (OR) mechanism. Overall, this review provides a quantitative framework for understanding the growth mechanisms, controlled by diffusion and surface adsorption in phytofabrication of AuNPs and AgNPs, enabling their controlled production with tailored properties for diverse applications.