Direct immobilization of gadolinium complex on silica particles and their MRI properties

This paper proposes a method for fabricating gadolinium diethylenetriamine pentaacetic acid-immobilized silica particles (SiO₂/Gd-DTPA). Preparation of a colloid solution of spherical silica particles with an average size of 101.7±11.7 nm was performed by a sol-gel method at 35°C using 0.2 M tetraethylorthosilicate, 25 M H₂O and 0.01 M NaOH in ethanol. Amino groups were introduced on the silica particles with 6 × 10^-3 M (3-aminopropyl)triethoxysilane (APES) at 35°C (SiO₂-NH₂), which resulted in their average particle of 80.5±9.7 nm. Gd-DTPA was immobilized on the SiO₂-NH₂ particle surface with 5 × 10^-4 M Gd-DTPA in 50/50 (v/v) water/dimethylformamide solution at 35°C, which provided their average particle of 101.6±12.3 nm. The APES-introduction and the Gd-DTPA-immobilization did not change the spherical structure, and shifted an iso-electric point of particles to higher pH for the APES-introduction and then to lower pH for the Gd-DTPA-immobilization, which indicated that APES and Gd-DTPA were successfully attached on the particle surface with no chemical damage. A relaxivity value for T₁-weighted imaging of the SiO₂/Gd-DTPA particle colloid solution was 2.7 mM^-1 s^-1, that was 64% of that for Magnevist.