A solution of 99.8% ethanol (30 mL), distilled water (3.0 mL), and 23% aqueous ammonia (1.5 mL) was prepared in a plastic vial. FexOy nanoparticles (1 mL, 15 nm diameter, Siliquan, Warsaw, Poland) were introduced into the solution under continuous stirring at ambient temperature. After 15 minutes, tetraethyl orthosilicate (TEOS, 150 μL) was added, and the vial was sealed. The reaction mixture was stirred for 24 hours at room temperature, yielding nanoparticles with a final concentration of 1.89 mg•mL⁻¹.