Ultrasmall Superparamagnetic Fe3O4 Nanoparticles Green-Synthesized with Cosmos caudatus : Phytochemical Surface Coordination and Suppression of MCF-7 Migration

Phytochemical-mediated synthesis of superparamagnetic iron oxide nanoparticles (SPION) is dominated by a narrow set of plant substrates, and extending this chemical space to phylogenetically distinct species remains an open question. Herein, we report the first application of Cosmos caudatus Kunth leaf extract, rich in quercetin glycosides, catechins, and chlorogenic acid, to the green sonochemical synthesis of superparamagnetic iron oxide nanoparticles (CC-SPION), benchmarked against an extract-free control (Bare-SPION). Acoustic cavitation combined with phytochemical reduction produced a crystalline inverse-spinel iron oxide in 25 min at near ambient temperature. TEM revealed near-monodisperse, semispherical primary particles of 7.30 ± 0.88 nm smaller than green-synthesized iron oxides in related studies; the TEM primary-particle diameter (7.30 nm) and XRD crystallite size (7.25 nm) were in close agreement, with FE-SEM reporting larger drying-induced aggregates (7.7–17.5 nm). Multipeak XRD analysis showed the crystallite size fell from 11.61 nm (Bare-SPION) to 7.25 nm (CC-SPION). Energy dispersive X-ray spectroscopy (EDX) corroborated the elemental compositions, whereas Fourier transform infrared spectroscopy (FTIR) substantiated the existence of Cosmos caudatus chemicals within the nanoparticle composition. This coordinated phytochemical corona raised the zeta-potential magnitude from −20.4 to −42.5 mV, conferring electrosteric stabilization (PDI ≈ 0.08). VSM confirmed superparamagnetism at 298 K (Ms = 43.99 emu/g; with no coercivity and remanence). CC-SPION was noncytotoxic to HEK-293 and MCF-7 cells across 31.25–500 μg Fe/mL (ISO 10993–5; viability ≥70%), reduced MCF-7 wound closure over 24–48 h, and showed dose-dependent cell association/localization. These findings establish C. caudatus sonochemistry as a route to mechanistically well-defined ultrasmall biocompatible SPION for prospective MRI and antimigratory applications.