Surfactant-free Gd3+-ion-containing carbon nanotube MRI contrast agents for stem cell labeling

Abstract

There is an ever increasing interest in developing new stem cell therapies. However, imaging and tracking stem cells in vivo after transplantation remains a serious challenge. In this work, we report new, functionalized and high-performance Gd³⁺-ion-containing ultra-short carbon nanotube (US-tube) MRI contrast agent (CA) materials which are highly-water-dispersible (ca. 35 mg ml⁻¹) without the need of a surfactant. The new materials have extremely high T₁-weighted relaxivities of 90 (mM s)⁻¹ per Gd³⁺ ion at 1.5 T at room temperature and have been used to safely label porcine bone-marrow-derived mesenchymal stem cells for MR imaging. The labeled cells display excellent image contrast in phantom imaging experiments, and TEM images of the labeled cells, in general, reveal small clusters of the CA material located within the cytoplasm with 10⁹ Gd³⁺ ions per cell.