A facile method to prepare high-performance magnetic and fluorescent bifunctional nanocomposites and their...

Magnetic and fluorescent bifunctional nanocomposites have great potential in biomolecule detection and biological imaging applications. So far, it remains a challenge to prepare bifunctional nanocomposites with high colloidal and fluorescent stability. To address this problem, we utilized a simple ring-opening reaction to conjugate Fe₃O₄ and CdZnSeS quantum dots (QDs). The surface amine groups of SiO₂-coated Fe₃O₄ nanoparticles (Fe₃O₄@SiO₂) opened the rings of the surface maleic anhydride groups of poly(styrene-co-maleic anhydride)-coated CdZnSeS QDs (QDs@PSMA), and then the resulting nanocomposite was functionalized with Jeffamine M-1000 polyetheramine (JMP) by a ring-opening reaction. The structures and properties of the bifunctional nanocomposites were fully characterized by transmission electron microscopy, dynamic light scattering, spectrofluorometry and vibrating sample magnetometry. The results indicated that the nanocomposites prepared by the conjugation method had dramatically higher quantum yields (QYs) than those prepared by the SiO₂ co-encapsulation method. After introducing JMP, the nanocomposites exhibited high fluorescent and colloidal stability over a wide pH range (pH 2-13), a low level of protein adsorption in PBS with 10% fetal bovine serum at 37 °C, and a negligible level of nonspecific binding when incubated with HeLa cells. Sandwich fluoroimmunoassay results indicated that the nanocomposites can be successfully applied in a variety of diagnosis and bioimaging applications.