Isolation, characterization, and acute toxicity assessment of brown seaweed Padina pavonica polysaccharide nanosuspensions in adult zebrafish (Danio rerio) with histopathological analysis of spleen and muscle

Marine seaweeds are a rich source of bioactive polysaccharides with significant biomedical potential due to their biocompatibility and diverse functional properties. The present study focuses on the extraction, characterization, biological activity, and acute toxicity assessment of a PVA-stabilized Padina pavonica polysaccharide nanosuspension. The extraction yield of the polysaccharide was approximately 16% (w/w). DLS analysis revealed particle sizes predominantly in the nanoscale range with a major intensity peak around 100 nm. SEM analysis further confirmed particle sizes of 100 nm. while zeta potential analysis showed a surface charge of approximately − 28 mV, indicating good colloidal stability. SEM analysis confirmed irregular to quasi-spherical morphology with moderate aggregation at the nanoscale. The nanosuspension exhibited concentration-dependent antibacterial activity against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa, with maximum inhibition zones of 20 mm, 25 mm, and 18 mm, respectively, at 100 µg/mL. Antioxidant activity assessed by DPPH assay demonstrated 63% radical scavenging at 100 µg/mL, with an IC₅₀ value of approximately 78 µg/mL, compared to 48 µg/mL for ascorbic acid. Acute toxicity evaluation in adult zebrafish showed high survival rates, with approximately 85% survival at 50 µg/mL and 65% at 100 µg/mL after 96 h, with no significant histopathological alterations in spleen and muscle tissues. Since mortality did not reach 50% within the tested range, LC₅₀ could not be determined. Overall, the findings demonstrate that the developed nanosuspension exhibits promising biological activity with low toxicity, supporting its potential application in nanomedicine and drug delivery.