Highly Uniform Superparamagnetic Mesoporous Spheres with Submicrometer Scale and Their Uptake into Cells

A new template approach was developed to synthesize highly uniform superparamagnetic mesoporous spheres with submicrometer scale, composed of silica and CoFe 2 O 4, in which mesoporous shell/solid core silica spheres with an average diameter of 505 nm are used as templates. Superparamagnetic phases are grown exclusively within mesoporous shells of the host silica spheres using a mixed solvent composed of ethanol and dioctyl ether, which results in maintaining the mesoporous nature of the host silica and retaining the superparamagnetic property. The samples annealed at temperatures above 773 K are converted into high-crystalline forms with enhanced coercivity and magnetization, which show a type IV isotherm typical for the mesoporous silica. The resulting superparamagnetic spheres are well-dispersible in water, have high magnetization values, and possess high surface areas. Cellular viability studies showed that the particles were readily endocytosed in human breast cancer (MCF-7) and mouse embryonic fibroblast (NIH-3T3) cells. Such highly uniform superparamagnetic spheres with submicrometer scale are suitable for renewable supports for catalytic applications and magnetic carriers for drug delivery.