Bifunctional heterometallic Ln3+–Gd3+ (Ln = Eu, Tb) hybrid silica microspheres: luminescence and MRI contrast agent property

Abstract

A novel series of homometallic and heterometallic lanthanide (Eu³⁺(Tb³⁺)–Gd³⁺) hybrid silica microspheres (EDTA-(Eu(Tb)-Gd)-TTA-SiO₂) are synthesized with 2-thenoyltrifluoroacetone (TTA) functionalized silane and ethylenediaminetetraacetic acid (EDTA) by sol–gel process, whose physical characterization are carried out and especially the luminescence and the magnetic resonance imaging (MRI) contrast agent properties are discussed. These hybrids present uniform silica microsphere morphology with particle size of 1 μm. Comparing to the homometallic hybrid silica microsphere EDTA-Ln-TTA-SiO₂ without Gd³⁺ ion, the heterometallic hybrid silica microspheres EDTA-Eu-Gd-TTA-SiO₂ exhibit stronger luminescent intensity, longer lifetime and higher luminescent quantum efficiency, which is due to the fact that inert ion Gd³⁺ can enhance the luminescence of the Eu³⁺ or Tb³⁺ within the hybrid system. In addition, the MRI relaxivity of the heterometallic lanthanide hybrid silica microspheres in water is assessed, showing a lower T1 relaxation rate than homometallic gadolinium hybrid one (EDTA-Gd-TTA-SiO₂). Both of them show higher T1 relaxation rate than the conventional Gd chelate of diethylenetriamine pentaacetic acid. These bifunctional hybrid materials exhibit both luminescent and MRI magnetic contrast agent properties, whose further investigation can be expected to have potential application in practical fields such as optical storage and sensors, etc.