Chemical Synthesis of Silver Nanoparticles: A Comparative Study of Antibacterial Properties

Background: Recent studies have suggested significant antimicrobial properties of silver nanoparticles (AgNPs), offering a ray of hope during the height of antibiotic resistance. However, their efficacy largely depends on the particle size and colloidal stability. Although higher stability of AgNPs is associated with improved antimicrobial activity, excessive stability weakens their reactivity with the bacterial membrane. The objective of the research is to evaluate different reducing agent combinations to achieve optimal particle size and colloidal stability for maximum bactericidal efficacy. Materials and Methods: The synthesis of AgNPs was carried out using silver nitrate using five different chemical reduction methods to compare their antimicrobial activity. After purification, the freeze-dried AgNPs were characterized by UV-visible spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and dynamic light scattering (DLS). The minimum bactericidal concentration (MBC) of the AgNP formulations were investigated by plate counting method against the methicillin-resistant E. coli. Finally, the synthesized AgNPs were tested against the resistant strains of E. coli, Salmonella, Klebsiella, Bacillus, and Staphylococcus by the well diffusion method to evaluate and compare their inhibition zones. Results and Discussions: The average particle size for different formulations of nanoparticles ranges from 30.91 nm to 93.85 nm, while the zeta potential ranges from -8.0 mV to -41.1 mV. The minimum bactericidal concentration (MBC) for all AgNP formulations was determined against gram-negative E. coli, and AgNPs synthesized with only trisodium citrate were found to be the most effective with 99.75% bactericidal efficacy at 20 ppm concentration due to their optimal particle size and stability. However, AgNPs synthesized with polyethylene glycol and polyvinyl pyrrolidine were found to be the most effective against the resistant bacterial strains in the well diffusion assay. Conclusion: The reducing agents affect the particle size and stability of synthesized AgNPs, resulting in significant variations in their antibacterial activity, warranting further study.