Iridium(III) and gadolinium(III) loaded and peptide-modified silica nanoparticles for photoluminescence and magnetic resonance (dual) imaging.

The combination of non-invasive fluorescence (FL) and magnetic resonance (MR) imaging can compensate for disadvantages in terms of resolution and sensitivity. However, the preparation of dual-mode probes simultaneously exhibiting strong brightness and high MR response is challenging. A multifunctional nanoprobe was synthesized for targeted photoluminescence (PL) and MR dual-modal imaging. It was obtained by conjugating iridium(III) complexes, gadolinium(III) and the peptide arginine-glycine-aspartate (RGD) onto silica nanoparticles (Ir@SiO2-Gd-RGD NPs). They are highly water soluble, have an average diameter of ~50 nm, and emit strong yellowish green PL (with excitation/emission peaks at 380/572 nm). Simultaneously, the nanoprobes exhibit high MR response with a longitudinal relaxation of 7.16 mM-1 s-1. Instead of simple encapsulation, Ir(III) complexes were covalently conjugated to silica matrix to enhance the chemical and photochemical stability of the nanoprobes. The excellent biocompatibility and PL/MR dual modal imaging capability of the NPs is demonstrated using HeLa cells and mice as models.