On the other hand, the weaker reducing agent trisodium citrate (TSC) contributes to the formation of relatively large
silver nanoparticles, having a wider size distribution. It can also result in a variation in the shape of the nanoparticles i.e.
spherical nanoparticles are accompanied with undesired generation of rods, cubes, and triangles. Thus, using either of
the reducing agents, it may be difficult to synthesize silver nanoparticles both, above 50 nm and below 10 nm having a
well-defined shape with desired monodispersity. The co-reduction method employing two different reductants (i.e., NaBH4
and TSC) may offer better control on nucleation and growth of nanoparticles. This may aid in the synthesis of different sizes of AgNPs using slight variations in the same protocol.
The preparation, characterization and size-specific antibacterial efficacy of silver nanoparticles over a wide size range is
described in this article. We refer to a facile, one pot synthesis for the generation of stabilized AgNPs over a wide size range (5–100 nm) achieved by varying the reaction conditions. The proposed dual thermal treatment encourages fast nucleation followed by growth of silver nanoparticles at approximately the same rate, resulting in relatively monodispersed nanoparticles. Also, a variation in pH of the reaction medium facilitated fine tuning of particle morphology from quasi-spherical to nearly spherical shape. Though in recent times few studies have evaluated the size-dependent antimicrobial activity of silver nanoparticles, a detailed and substantial study to explore the entire size range from 5–100 nm, is lacking. The current study also investigates a size-selective comparison of their antimicrobial activity against various Gram-positive and Gramnegative bacterial strains. A comprehensive study of antimicrobial activity was made on the basis of bacterial growth kinetics using different amounts of silver nanoparticles, along with MIC/MBC values determined based on liquid cultures using different sizes of silver nanoparticles. While we limit our study to the antibacterial application, relatively larger nanoparticles synthesized using our method can potentially be exploited for other interesting purposes, such as, SERS based diagnostics, bio-sensing, and bio-imaging.