Ternary ZnO/ZnS/γ-Fe2O3 hollow sphere with surface hole: Microwave-enhanced rapid synthesis, bifunctional property, and immobilization of serum protein

High-yield ternary ZnO/ZnS/γ-Fe2O3 hollow spheres with an average size of 600 nm were prepared rapidly via a microwave-irradiation route; the reaction period is as short as 30 min. The hollow spheres are composed of numerous ZnO, ZnS, and γ-Fe2O3 crystallites and the mechanism responsible for their formation is Ostwald ripening. Every hollow sphere has a distinct surface hole with the pore size of tens of nanometers or hundreds of nanometers. The characterizations of the physical properties of the hollow spheres reveal that they have integrated the superparamagnetism of γ-Fe2O3 and the photoluminescence property of ZnO and ZnS. Furthermore, since the pore size of the hole on the surfaces of the hollow spheres is large enough to accommodate bovine serum albumin (BSA) molecule with a giant size, the hollow spheres can not only adsorb BSA with their external surfaces but also trap the proteins in their interiors. Per gram hollow sphere can immobilize 178.6 ± 34.5 mg of BSA when they are interacted with 600 μg/mL BSA solution for 24 h. The investigations on the releasing behavior of BSA by the hollow spheres reveal that BSA molecules on the external surfaces of the spheres are desorbed quickly, while those confined in the interiors of the spheres are released smoothly and the process is sustained over 10 days. The accumulative releasing percentage of BSA is about 51% in 10 days.