Unraveling the Positive Role of Fe ₃ O ₄ Nanoparticle Size and Coating in Wheat Growth and Oxidative Resistance

The application of ferroferric oxide nanoparticles (Fe 3 O 4 NPs) in nanoenabled agriculture has expanded rapidly, yet the mechanisms linking their physicochemical properties to crop growth remain unclear. This study aims to elucidate how the surface coatings and particle sizes of Fe 3 O 4 NPs regulate wheat root development and metabolic responses. Wheat roots were exposed hydroponically to Fe 3 O 4 NPs with different coatings and sizes at 0.01–10.0 mg/L. Citrate (Cit)- and polyvinylpyrrolidone (PVP)-coated large-sized NPs (50, 100 nm) and 20 nm naked Fe 3 O 4 NPs at 10 mg/L significantly enhanced root morphological traits (4%–66%). Fe 3 O 4 NPs effectively scavenged •OH, •O 2 –, and H 2 O 2 (37%–84%), while 20 nm naked and large Cit-/PVP-coated Fe 3 O 4 NPs upregulated carbohydrate, amino acid, and lipid metabolites related to ROS detoxification and root growth. Response ratio, PLS-PM, and relative importance analyses revealed coatings as the dominant factor followed by size. These findings are critical for predicting the role of NPs in influencing sustainable agriculture.