Synthesis of highly monodisperse superparamagnetic iron oxide core@mesoporous silica shell particles with independently tunable size, and porosity

Superparamagnetic iron oxide nanoparticles, SPIONs, especially in the form of nanoscopic aggregates thereof, find broad applications as magnetic resonance imaging contrast agents, as biological tools for straightforward separation of biomolecules and cells, as magnetically tunable colorimetric sensors exhibiting structural colors, etc. Furthermore, if the SPIONs are covered with another oxide, typically silica, the size and refractive index of the particles can be modified. In addition, if the silica layer is mesoporous additional functionalities can be introduced. Such particles could serve as, for example, theranostic nanoparticles capable of serving both as drug carriers and contrast agents, as easily separable high-capacity adsorbers, and if the particles are monodisperse, colorimetric sensors. Many reports cover the synthesis of such SPION core-silica shell particles, but to date the structural tunability and reproducibility aspect has not received deserved attention. Here we report highly reproducible syntheses leading to SPION cores carrying silica shells with independently tunable shell thicknesses and porosities. The products are highly monodisperse in all cases, as evidenced by the fact that pellets of the particles show structural colors. The shell formation process is followed in detail, and is related to the applied synthesis parameters, which allows for rational further fine-tuning of the structural characteristics of the coreshell particles for a given application.

Automated summary

Superparamagnetic iron oxide nanoparticles, particularly in the form of nanoscopic aggregates, have various applications in contrast agents, biological tools, and sensors. The particle size and refractive index can be modified by coating the nanoparticles with another oxide, typically silica. Additionally, introducing mesoporous silica layers enables the nanoparticles to serve as theranostic nanoparticles and high-capacity adsorbers, as well as colorimetric sensors.