Biosynthesized iron oxide nanoparticles using Trichoderma harzianum with applications for phytopathogen control.

In the pursuit of a sustainable transition toward green synthesis, the biological production of nanomaterials emerges as an attractive alternative for generating nanomaterials with controlled physicochemical properties. In this work, Fe-based nanostructures were biosynthesized using Trichoderma harzianum with iron precursor concentrations of 5 mM (Fe5) and 10 mM (Fe10), followed by thermal treatment. SEM, AFM, and TEM analyses revealed that precursor concentration governs particle size and aggregation, while annealing drives the phase evolution from Fe3O4 based composition in the as-synthesized nanomaterials to a crystalline α-Fe2O3 phase, as confirmed by XRD and XPS. These techniques further indicate that this transformation is associated with the removal of capping biomolecules and the oxidation of Fe(II) to Fe(III). Biologically, Fe5 and Fe10 acted as potent biostimulants, enhancing T. harzianum growth, sporulation, and pigmentation without inhibition. Dual-culture assays demonstrated that both materials significantly increased the fungus's antagonistic activity against Fusarium oxysporum, Fusarium verticillioides, and Phytophthora infestans. These results highlight the potential of biosynthesized Fe oxide nanoparticles as dual-function platforms that couple nanotechnology and biological control for sustainable crop protection.