Bifunctional superparamagnetic-luminescent core-shell-satellite structured microspheres: preparation, characterization, and magnetodisplay application

We present a general process that allows the convenient production of bifunctional superparamagnetic-luminescent composite particles (CPs) by the direct self-assembly of nanoparticles on host 3 mm silicon oxide microspheres (SiMS). Fe3O4 nanoparticles (FeNPs) can be directly assembled layer-by-layer (LBL) with a dithiol agent onto the host surface that modified high-density surface thiol groups through the strong coordination interactions between metal cations and thiol groups. The resulting structures can be further conveniently coated with a layer of normal silica, with thiol groups to stabilize the assemblies and immobilize CdTe quantum dots (QDs). As the entire fabrication process is free of complicated surface modification procedures, the rich thiol groups among the FeNPs and CdTe QDs are not disturbed significantly. Therefore, the core-shell-satellite structured SiMS@FeNPs@CdTe CPs retain their original properties including highly efficient superparamagnetism and luminescence. A home-made transparent sandwich device with solenoid coils (TSDSC) containing the aqueous dispersions of these CPs was used to observe reversible magnetically responsive transmittance and luminescence due to the particle chaining behavior in the presence of an alternating magnetic field (AMF). The results suggest that the specific superparamagnetism and luminescence of nanoparticles can be efficiently endued on microscale particles. Such an assembly approach will provide the research community with a highly versatile, configurable, scalable, and reproducible process for the preparation of various multifunctional structures.