Facile synthesis of QD-anchored composite particles with magnetite cluster cores (nFe3O4@SiO2@QDs)

Magnetism-controlled fluorescent composite particles (nFe3O4@SiO2@QDs) were prepared as QD-anchored silica nanoparticles with magnetite cluster cores. First, citrate-capped magnetites (C-Fe3O4) were prepared by the co-precipitation method and subsequently complexed with 3-aminopropyl-trimethoxysilane (APTMS) at room temperature, consequently leading to the formation of magnetite clusters (A-nFe3O4) with alkoxy terminated interfaces. The sol–gel reaction between A-nFe3O4 and tetraethoxysilane (TEOS) produced the core-shell nFe3O4@SiO2. The resulting core-shell particles exhibited superparamagnetic properties and controllable magnetism simply by adjusting the thickness of nonmagnetic silica layer. After then, amine-terminated nFe3O4@SiO2 (NH2–nFe3O4@SiO2) was conjugated with carboxy quantum dots (QDs) using an EDC coupling agent. The QD conjugation with NH2–nFe3O4@SiO2 of lower pH exhibited the higher photoluminescence (PL) intensity, and the resulting composite particles (nFe3O4@SiO2@QDs) can be a useful biomedical agent. This chemical strategy can be further applied to prepare the core-shell magnetic nanostructure with various oxide layers for specific applications.