Abstract
Green synthesis of nanoparticles (NPs) employs biological resources such as plant extracts, microorganisms, and biomolecules as reducing and stabilising agents, offering an environmentally benign alternative to conventional physical and chemical methods. This approach minimises the use of toxic reagents and harsh conditions, reduces energy consumption, and often yields nanomaterials with superior biocompatibility and functional surface chemistry. Plant-mediated and microbe-mediated routes have emerged as the most widely explored green strategies for synthesising metal and metal-oxide nanoparticles including silver, gold, platinum, palladium, zinc oxide, titanium dioxide, and iron oxides. Phytochemicals or microbial metabolites act as electron donors (reducing metal ions) and as capping agents that control nucleation, growth, and stabilization, thereby influencing size, shape, crystallinity, and surface charge. Biogenic nanoparticles exhibit promising applications across biomedicine, catalysis, environmental remediation, food and agriculture, and sensing, frequently matching or surpassing the performance of conventionally produced nanomaterials while offering improved sustainability. Nonetheless, challenges remain, including batch-to-batch variability, incomplete mechanistic understanding, scale-up limitations, and the need for systematic toxicological and life-cycle assessments.