Biocompatible goethite crystal phase iron oxide nanoparticles from Pithecellobium dulce exhibit dye degradation potential and protective effect against aquatic pathogen Aeromonas hydrophila infection in a zebrafish model

• Goethite phase IONPs were green synthesized using P. dulce fruit extract. • IONPs effectively degraded methylene blue, methyl orange, and malachite green dyes. • IONPs showed antimicrobial activity against A. hydrophila with MIC and MBC of 73.34 ± 2.81 and 89.60 ± 3.74 µg/mL, respectively. • IONPs' antimicrobial action involves membrane damage, ROS generation, and biomolecules leakage. • IONPs are biocompatible up to 50 µg/mL and alleviate zebrafish embryos mortality rate from A. hydrophila infection. This study investigated green synthesis of iron oxide nanoparticles (IONPs) using Pithecellobium dulce fruit extract and evaluated their antioxidant, dye degradation, and antimicrobial properties against Aeromonas hydrophila . Q-TOF LC/MS analysis of P. dulce fruit extract revealed bioactive compounds including gallic acid, naringenin, myricetin 3-O-rhamnoside, alpha – linolenic acid, kaempferol 3-O-glucoside, and quercetin-O-glucoside. FTIR analysis confirmed the green synthesis of IONPs. The XRD pattern indicated IONPs were in the goethite phase. The IONPs showed a stability of − 30.9 mV and an average size of 16.86 nm. The IONPs exhibited antioxidant activity in DPPH and ABTS assays, with IC 50 values of 64.06 ± 2.80 and 68.29 ± 0.89 µg/mL, respectively. Dye degradation was assessed using methylene blue (MB), methyl orange (MO), and malachite green (MG) dyes. At 14 min, MG, MB, and MO degraded by 36.8, 47, and 59.2%, respectively, indicating that MG is more stable than MB and MO. Antimicrobial activity against A. hydrophila revealed minimum inhibitory (MIC) and minimum bactericidal (MBC) concentrations of 73.34 ± 2.81 and 89.60 ± 3.74 µg/mL, respectively. IONPs exhibited antimicrobial activity through membrane damage, ROS generation, and protein and nucleic acid leakage. Biocompatibility tests using zebrafish embryos showed no toxicity and mortality up to 50 and 100 µg/mL IONPs, respectively. The protective efficacy of IONPs (up to 50 µg/mL) against A. hydrophila infection in zebrafish embryos showed a dose-dependent reduction in developmental abnormalities and mortality rates using the immersion batch technique. This study demonstrates potential of green-synthesized goethite IONPs for managing A. hydrophila infections in aquaculture and environmental remediation.