Eco-engineered selenium nanoparticles via Mentha arvensis phytochemistry for dual mitigation of methylene blue dye pollution and aquatic pathogen Aeromonas hydrophila: Mechanistic and biocompatibility insights

Mentha arvensis leaf extract was used to synthesize selenium nanoparticles (MA-SeNPs) via a green chemistry approach. Q-TOF LC/MS analysis revealed the presence of phenolic acids, flavonoids, sterols, coumarins, and triterpenoids in the extract, which acted as reducing and stabilizing agents during nanoparticle formation. However, despite the growing interest in green-synthesized SeNPs, the use of M. arvensis phytochemistry for the fabrication of SeNPs and the evaluation of their dual functionality in dye remediation and aquatic pathogen control remain largely unexplored. As synthesized MA-SeNPs exhibited a distinct UV–Vis absorption peak at 440 nm, an apparent optical bandgap of 3.52 eV, and a zeta potential of −26.9 mV, indicating good colloidal stability. FTIR analysis confirmed the involvement of phytochemicals from M. arvensis leaf extract in the synthesis of MA-SeNPs. SEM analysis showed predominantly spherical MA-SeNPs with particle sizes ranging from 15 to 90 nm (average 46.1 nm), whereas DLS analysis revealed a larger hydrodynamic diameter of 93 d. nm, reflecting the contribution of surface-bound phytochemicals and the solvation layer. The amorphous nature of the MA-SeNPs was determined by XRD. The MA-SeNPs demonstrated efficient photocatalytic degradation of methylene blue (MB) dye, achieving approximately 88% degradation within 240 min and following pseudo-first-order kinetics. The nanoparticles exhibited potent antibacterial activity against the aquatic pathogen Aeromonas hydrophila , with an MIC of 81 μg/mL and an MBC of 115 μg/mL. Microscopic observations revealed dose-dependent inhibition of A. hydrophila biofilm formation by MA-SeNPs. The antibacterial mechanism involved reactive oxygen species (ROS) generation, membrane disruption, and leakage of cellular contents. MA-SeNPs were biocompatible with zebrafish embryos at concentrations ≤150 μg/mL and provided dose-dependent protection against A. hydrophila infection, with near-complete embryo survival at 100 μg/mL. These findings highlight the potential of MA-SeNPs as eco-friendly and effective antimicrobial agents for controlling A. hydrophila infection in aquaculture.