Study of the Magnetic Properties of Fluorescent Composite Nanoparticles

Luminescent magnetic nanostructures have significant applications across various scientific and technological domains. In modern industry, metal-based structural materials are widely utilized in the development of advanced devices and components. To ensure safety and prevent malfunctions, non-destructive testing methods are employed to detect structural defects without interrupting production processes. This study aims to develop synthesis methods for fluorescent composite nanoparticles of iron oxides with varying dispersions, incorporating a SiO₂ shell, and to investigate their magnetic and spectral-optical properties. A modified aging method—excluding nitrogen bubbling and utilizing gentle stirring—is proposed for nanoparticle synthesis. The principles of forming a SiO₂ shell on the surface of iron oxide nanoparticles (Fe₃O₄, γ-Fe₂O₃) of various sizes are established. The relationship between shell thickness, precursor concentration, and mixing duration is analyzed. Additionally, a method for functionalizing iron oxide nanoparticles with a fluorescent dye (fluorescein ethyl ether-O-bromoethyl) via an aminated surface layer using 3-aminopropyltriethoxysilane is presented. Shell thicknesses up to 35 nm were successfully achieved using a modified Stöber technique.