Green synthesis of gold nanoparticles using Gracilaria corticata: Evaluation of acute toxicity, genotoxicity, and histopathological alterations in zebrafish (Danio rerio).

Gold nanoparticles (AuNPs) synthesized using green methods have gained significant attention for their environmental, biomedical and aquaculture applications. In the present study, AuNPs were biosynthesized using Gracilaria corticata extract and evaluated for their physicochemical characteristics, biological activities, and toxicological impact. Phytochemical screening confirmed the presence of bioactive compounds, including flavonoids, tannins, saponins, and alkaloids, which is interference to nanoparticle synthesis and stabilization. UV-Visible spectroscopy showed a characteristic surface plasmon resonance peak at 531 nm, while FTIR analysis indicated the involvement of hydroxyl, aromatic, and amine functional groups. SEM analysis revealed spherical and hexagonal nanoparticles with an average size of 2.6 nm, and EDS confirmed the elemental composition of gold. The synthesized AuNPs exhibited dose-dependent anti-inflammatory activity and significant antioxidant potential, as demonstrated by DPPH and nitric oxide scavenging assays. Toxicity assessment in Danio rerio revealed concentration- and time-dependent effects, with reduced survival and behavioral alterations at higher concentrations (100 and 250 μg/ml). Genotoxic evaluation using the comet assay showed increased DNA damage in gill and liver tissues, while histopathological analysis revealed hepatocellular vacuolation without severe necrosis. These findings suggest that although biosynthesized AuNPs possess promising bioactive properties, they may induce sublethal toxic effects at elevated concentrations, highlighting the importance of dose optimization for environmental and biomedical applications.