Figure 1.

Diverse synthesis routes of silver nanoparticles (AgNPs). (a) Top-down and bottom-up methods, (b) physical synthesis method, (c) chemical synthesis method, and (d) plausible synthesis mechanisms of green chemistry. The bio-reduction is initiated by the electron transfer through nicotinamide adenine dinucleotide (NADH)-dependent reductase as an electron carrier, forming NAD⁺. The resulting electrons are obtained by Ag⁺ ions, which are reduced to elemental AgNPs (Images adapted and modified from [21]).