Lanthanide Loaded Zeolites, Clays, and Mesoporous Silica Materials as MRI Probes

Zeolites, clays, and mesoporous silica materials offer the possibility to be loaded with Ln3+ ions either by means of ion exchange of the cations that are balancing the negative charge of the framework or by grafting of Ln3+ chelates to the framework. In this Microreview, the structures of the materials used up to now are described and related to their stabilities and relaxometric behavior. The possible exploitation of the unique features of these materials as both positive and negative MRI contrast agents in multimodal probes and in theranostics are discussed.