Magnetic/fluorescent multi-functional PGMA@Fe3O4@SiO2@SiO2-Eu microspheres: A strategy of partitioning europium complex and Fe3O4 nanoparticles

This study aims to advance the development of magnetic fluorescent polymer microspheres for biomedical detection applications. Conventionally, dopants have utilized europium(III) (Eu(III)) organic complexes due to their high compatibility with polymers and strong fluorescence. However, as the common magnetic material Fe 3 O 4 can quench their fluorescence, it is hard to synthesize Eu complex-doped magnetic fluorescent materials. To maintain fluorescence in the presence of magnetic parts, in this work, we synthesized Eu-doped magnetic microspheres with multi-layered structure. Firstly, poly-(glycidyl methacrylate) (PGMA) microspheres were prepared as templates and subsequently coated with layers of Fe 3 O 4 and SiO 2 . Then, the synthesized Eu(TTA) 3 (TPPO) 2 were added into PGMA@Fe 3 O 4 @SiO 2 microspheres in either basic or acidic conditions, and covered them with an extra sol–gel layer of silica at the same time. The microspheres exhibit a core–shell structure with sub-micron dimensions (580 nm) and possess favorable superparamagnetic properties ( M s = 22.02 A·m 2 /kg, M r = 1.37 A·m 2 /kg, H c = 0.242 A/m). But the fluorescence of Eu 3+ are significantly quenched by Fe 3 O 4 , O–H oscillators, and N–H oscillators. Finally, to exclude the quenching mentioned above, the first pure SiO 2 shielding layer and the second Eu(TTA) 3 (TPPO) 2 -dispersed SiO 2 layer were coated onto PGMA@Fe 3 O 4 microspheres to prevent the energy transfer due to the quenching centers and hold the fluorescence of Eu 3+ . These findings underscore the considerable potential of these microspheres exhibiting rapid magnetic separation and stable fluorescence for bioimaging and biosensing applications.