Optimizing Amine Functionalization of Maghemite Nanoparticles Through Controlled Hydroxylation and Silica Interlayer Engineering

Maghemite (γ-Fe2O3) nanoparticles are widely used in biomedical, catalytic, and environmental applications owing to their superparamagnetic properties and surface tunability. Functionalization with primary amine groups via 3-aminopropyltriethoxysilane (APTES) is commonly employed to enable the covalent immobilization of biomolecules and other functional species. The efficiency of this silanization process depends significantly on the density of surface hydroxyl groups, which serve as reactive sites for silane coupling. In this study, the impact of acid and base pretreatments on the surface hydroxylation of γ-Fe2O3 nanoparticles and the subsequent APTES grafting performance was systematically evaluated. Intermediate modification using tetraethoxysilane (TEOS) was explored as a strategy to enhance silanization by forming a hydroxyl-rich silica interlayer. Fourier transform infrared spectroscopy and zeta-potential measurements were performed to assess surface chemistry and functional-group incorporation. The results indicate that acid pretreatment significantly increases the availability of reactive –OH groups, while TEOS-assisted silanization improves the uniformity and density of surface-bound amine groups. These findings highlight the critical role of surface conditioning and sequential modification in achieving the controlled and robust amine functionalization of iron oxide nanoparticles. The developed approach provides a foundation for the rational design of surface engineering protocols for high-performance magnetic nanomaterials.