Biomedical functionalities and teratogenic risks of bioengineered ZnO nanoparticles in post-fertilization zebrafish...

Zinc oxide nanoparticles (ZnO NPs) are widely utilized in several commercial applications. Although their toxicity and associated oxidative stress have been extensively studied, the toxicity they induce during embryonic development remains largely unknown. In this study, ZnO NPs were fabricated via a green synthesis approach using the leaf extract of Aegle marmelos (Am@ZnO NPs), and their developmental toxicity toward post-fertilized zebrafish embryos was investigated. The synthesized Am@ZnO NPs exhibited a UV-Vis absorbance peak at 372 nm. X-ray diffraction (XRD) analysis confirmed the presence of crystalline material with a grain size of 14.16 nm. The functional molecules involved in synthesis were identified using Fourier-transform infrared (FTIR) spectroscopy. Notably, distinct IR bands were recorded at 3501, 3120, 2785, 2198, 2064, 1885, 1530, and 875 cm^-1 for both the leaf extract and Am@ZnO NPs. Scanning electron microscopy (SEM) showed predominantly spherical-shaped particles, while transmission electron microscopy (TEM) revealed hexagonal morphologies, with particle sizes ranging from 10 to 20 nm and a mean particle size of 16 ± 1.2 nm nm. Energy-dispersive X-ray spectroscopy confirmed the weight percentages of Zn and O as 77.91% and 22.09%, respectively. The well diffusion assay exhibited an inhibition zone of 25.6 ± 0.9 mm at 100 μg/mL against Corynebacterium striatum accompanied by a significant (p < 0.05) reduction in biofilm formation (94.40%) at the same concentration. Furthermore, the radical scavenging activity reached 86.36% for DPPH and 75.32% for H₂O₂ at 100 μg/mL (p < 0.05). Embryotoxicity assays revealed that the no statistically significant embryonic mortality was observed in zebrafish exposed to 2-10 μg/mL of Am@ZnO NPs compared to the control group. At 96 hpf, the highest dose (10 μg/mL) resulted in a minimal mortality rate of 20%. Notably, embryos treated with 2, 4 and 6 μg/mL of Am@ZnO NPs exhibited significantly lower hatching rates of 0, 4 and 8%, respectively, at 96 hpf. Moreover, severe developmental deformities-including unhatched coagulated eggs, tail malformations, lordosis, kyphosis, scoliosis, and a lack of somite formation were observed at 96 hpf. These findings help elucidate the toxicity mechanisms of Am@ZnO NPs during zebrafish development. Furthermore, this study provides the scientific community with key insights into nano-embryotoxicity, establishing a baseline for future research to design safer nanomaterials.