Functionalized Iron Oxide-Silver Nanohybrids for Enhanced Germination of Sorghum

In this work, hydrophilic FeOx-AgNPs nanohybrids were obtained by covalent interaction between functionalized maghemite nanoparticles (γ-Fe2O3NPs) and silver nanoparticles (AgNPs). An in situ chemical reduction of the AgNO3 precursor was carried out in the presence of sodium 3-mercapto-1-propanesulfonate (3MPS) stabilizer to further improve colloidal stability and aqueous dispersibility of the nanohybrids. The bifunctional linker (3-mercaptopropyl)trimethoxysilane (MPTMS) enabled the γ-Fe2O3NPs surface coating through Fe–O–Si chemical bonds, exposing the –SH ending moiety for covalent decoration of AgNPs-3MPS through covalent Ag–S bonds. Two nanohybrids, namely, FeOx-AgNPs_1 and FeOx-AgNPs_10, were obtained by tuning the Fe/Ag weight ratio, resulting in Ag content of 4–15 wt %, as confirmed by inductively coupled plasma optical emission spectrometry (ICP-OES) measurements. The deep characterizations by UV–Vis spectroscopy, dynamic light scattering (DLS) and ζ-potential, far- and mid- Fourier-transform infrared (FTIR) and Raman spectroscopy, high-resolution transmission electron microscopy (HR-TEM), powder X-ray diffraction (PXRD), elemental analysis, and magnetic susceptibility measurements confirmed their colloidal nature, aqueous stability, surface functionalization, and ferromagnetic behavior. Both hybrids were tested as nanoprimers (0.01–100 ppm concentration range) on Sorghum bicolor (L.) Moench Bianca seeds. FeOx-AgNPs_1, containing the lower Ag content, significantly improved the germination rate without phytotoxic effects at lower concentrations (0.01–1 ppm, i.e., 0.0015–0.15 ppm of metallic Ag). 1H NMR metabolomic analysis revealed a dose-dependent regulation of amino acid and carbohydrate content, indicating an osmotic adjustment mechanism. The results of this research highlight the possibility of combining γ-Fe2O3NPs-MPTMS with AgNPs-3MPS in a single covalent hybrid nanostructure, demonstrating their potential within the frame of nanoprimers as a sustainable alternative to conventional agrochemical treatments.