Green Pathways to Silver Nanoparticles: A Comparative Review of Plant, Microbial, and Biopolymer-Mediated Synthesis

Silver nanoparticles (AgNPs) have emerged as one of the most extensively investigated nanomaterials due to their distinctive physicochemical properties, including nanoscale dimensions, large surface area-to-volume ratio, surface plasmon resonance, and broad-spectrum antimicrobial activity. These attributes have enabled their application in pharmaceuticals, biomedical devices, wound management, diagnostics, food packaging, and environmental remediation. Conventional physical and chemical synthesis methods frequently employ toxic reagents, hazardous solvents, and energy-intensive processes, raising serious concerns regarding environmental sustainability and biocompatibility. Consequently, green synthesis strategies have gained prominence as eco-friendly alternatives aligned with the principles of green chemistry. This review presents a comprehensive and critical comparison of plant-mediated, microbe-mediated, and biopolymer-assisted synthesis of silver nanoparticles. Mechanistic pathways, influencing parameters, advantages, limitations, and recent advancements associated with each approach are systematically discussed. Particular emphasis is placed on nanoparticle characterization, biological and pharmacological activities, biocompatibility, toxicity, scalability, and regulatory considerations. Comparative evaluation reveals that while plant- and microbial-mediated routes offer simplicity and biological functionality, biopolymer-assisted synthesis provides superior reproducibility, stability, and pharmaceutical suitability. The review highlights existing challenges and future perspectives for the clinical and industrial translation of green-synthesized silver nanoparticles.