Sustainable Synthesis of Silver Nanoparticles (Chemical vs Biological) and Their Antimicrobial Activity against Clinical Pathogens

Silver nanoparticles synthesized via fungal-mediated processes represent an innovative and environmentally sustainable alternative to conventional chemical methods, reducing toxicity and ecological risks without compromising their antimicrobial activity, particularly against multidrug-resistant bacteria. This study aimed to optimize the synthesis of silver nanoparticles using chemical and biological approaches, characterize their physicochemical properties, and evaluate their antibacterial efficacy. Chemical synthesis employed sodium borohydride and carboxymethylcellulose, optimized via factorial design, with optimal conditions determined as 0.7 g L^-1 carboxymethylcellulose, 6.0 × 10^-3 mol L^-1 sodium borohydride, and 3.5 × 10^-4 mol L^-1 silver nitrate. Biological synthesis utilized <i>Aspergillus niger</i> in a glucose-casein hydrolyzate medium, varying inoculum volume (1 mL, 1.5 mL, and 2 mL). Characterization techniques included UV-vis spectroscopy, total reflection X-ray fluorescence, and transmission electron microscopy. The microdilution assay evaluated antibacterial efficacy against bacterial strains, including ampicillin-resistant <i>Pseudomonas aeruginosa</i>. Results show that chemically synthesized silver nanoparticles are smaller, more uniform, and consistently spherical than biologically synthesized nanoparticles. Biologically synthesized nanoparticles also display predominantly spherical morphology, with similar average diameters across different inoculum volumes, although lower inoculum concentrations tend to yield smaller particles. Nanoparticles produced through chemical and biological methods exhibit bacteriostatic and bactericidal properties; however, those synthesized chemically consistently outperform their biological counterparts against all bacterial strains tested. Both nanoparticle types demonstrate significant efficacy against antibiotic-resistant bacteria, reinforcing their potential as alternative antimicrobial agents. These findings emphasize the value of biological synthesis approaches for producing sustainable nanomaterials and offer a viable strategy to address the global health threat of drug-resistant pathogens.