High content and dispersion of Gd in bimodal porous silica: T2 contrast agents under ultra-high magnetic fields

Abstract

Silica-based UVM-7-type bimodal mesoporous materials with high gadolinium content (∞ ≥ Si/Gd ≥ 13) have been synthesized through a one-pot surfactant-assisted procedure from hydroalcoholic solution using a cationic surfactant as template, and starting from atrane complexes of Gd and Si as inorganic precursors. The novel synthetic pathway developed in the study preserves the UVM-7-type architecture while optimizing the dispersion of the Gd-guest species at the nanoscale and even at atomic level. It has been determined that the number of Gd atoms forming clusters is always less than 10. The behaviour under exposure to ultra-high magnetic fields reveals a significant increase in the transversal relaxivity value when compared with related materials in the bibliography. Their activity as T2 instead of T1 contrast agents is discussed and explained considering the high Gd-dispersion and concentration, nature of the materials as well as due to the high magnetic fields used, typical of MRM studies. The absence of toxicity has been confirmed in preliminary cell cultures “in vitro” and the degradation of the solids studied under biological conditions. Results suggest that the atrane route could be a suitable synthesis approach for the preparation of Gd containing contrast agents. • Very high Gd-containing (Si/Gd = 11–13) hierarchical bimodal porous silicas have been synthesized. • The materials are monophasic samples without segregation of Gd 2 O 3 nanodomains. • The Gd centres result highly dispersed in the form of Gd n clusters (n < 10). • The high Gd concentration and dispersion confers these materials interest as contrast agents. • A remarkable increase of the T2 relaxivity when working under ultra-high magnetic fields is observed.