Unlocking the potential of gold nanoparticles with insights into green synthesis, mechanisms, characterization and multifunctional applications.

Gold nanop articles (AuNPs) have garnered significant attention in biomedical research owing to their unique physicochemical properties, including biocompatibility, tunable stability, and versatile surface chemistries. However, conventional physical and chemical synthesis methods often depend on hazardous reagents and energy-intensive conditions, raising environmental and health concerns regarding their use. Green synthesis has emerged as a promising eco-friendly alternative, employing biological entities such as plants, bacteria, fungi, and algae as natural biofactories. This review explores advances in the biogenic synthesis of AuNPs and outlines the mechanisms of bioreduction and capping mediated by diverse biomolecules. A detailed overview of characterization techniques, including spectroscopy and microscopy, is provided to demonstrate the relationship between nanoparticle properties and their biomedical efficacy. The multifunctional applications of green-synthesized AuNPs are examined, with an emphasis on their antibacterial, antifungal, antiviral, anticancer, anti-inflammatory, and antioxidant properties. Mechanistic insights, including membrane disruption, reactive oxygen species (ROS) generation, DNA damage, and apoptosis induction, are discussed. Finally, this review highlights the challenges hindering large-scale production and clinical translation, including the need for standardized protocols and mechanistic understanding, while offering perspectives on future research directions. These findings establish a foundation for innovations in nanomedicine, underscoring the importance of bio-based synthesis for safe and effective healthcare solutions.