Plant-Mediated Green Nanoparticles in Modern Drug Delivery: Advances in Synthesis, Characterization, Therapeutic Applications, and Safety Challenges

Background: With the increasing demand for biocompatible, cost-effective, and environmentally friendly nanocarriers, plant-mediated (green) synthesis of metallic and metal-oxide nanoparticles has become a major direction in pharmaceutical research. Phytochemical synthesis uses the polyphenols, flavonoids, terpenoids, and proteins available in plant extracts as reducing and capping agents to produce nanoparticles that are less toxic and more biologically active than those produced by conventional physicochemical methods. Objective: This study aims to summarise the literature on the synthesis, characterisation, and therapeutic potential of plant mediated nanoparticles over the past five years (2020-2025), focusing on their incorporation into current drug delivery systems. Methodology: We used PubMed, ScienceDirect, Web of Science/Scopus, SpringerLink, and Google Scholar to conduct the structured narrative review. We screened articles published from January 2020 to September 2025 using combinations of keywords, including green synthesis, characterisation, phytochemicals, drug delivery, plant-mediated nanoparticles, and nanotoxicology. We included articles only if they reported a synthesis mechanism, physicochemical characterisation, or a biomedical/toxicological outcome. Findings: Plant-extracted-synthesised silver, gold, zinc oxide and iron oxide nanoparticles show good physicochemical characteristics (around 1-100 nm), which are supported by the results of UV-Vis, FTIR, and XRD, TEM/SEM and dynamic light scattering studies show antimicrobial, anticancer, antioxidant, and targeted drug-delivery activities. However, important barriers to translation remain, including batch-to-batch variability, incomplete phytochemical characterisation, and insuficient long-term toxicity data. Conclusions: Plant-mediated nanoparticles are a potential scalable alternative for next-generation drug delivery, but future applications require standard synthesis protocols and thorough safety testing.