親水性ナノダイヤモンド粒子による高感度MRI用ナノ造影剤の作製

抄録

Nanodiamond (ND) particles are nano-scale materials that have recently been attracting major attention for biological purposes, owing to their high biocompatibility and chemical stability. ND also possesses nanostructures, which makes it an ideal size for various purposes especially in nanotechnology.

An MRI contrast agent could be a suitable target for the practical use of nanodiamond particles. MRI contrast agents with a diameter of 3–10 nm could be selectively ingested by lymphatic vessels through simple subcutaneous injection, which could be then filtered in the kidney. However, ordinary contrast agents (Gd-DTPA) were smaller than 1 nm in diameter, and thus the MR imaging of the lymphatic system had not been successfully achieved. In this study, highly-dispersive carboxylated-nanodiamond (CND) particles with a diameter of ~5 nm were employed as a platform for the subsequent condensation of gadolinium-complexes (Gd-DTPA-CND). CND particles were employed not only for their nanoscale size, but also for the evasion of unnecessary aggregations of ND particles in water.

The diameter of Gd-DTPA-CND particles in distilled water was measured by the dynamic light scattering (DLS), revealing that the particles possessed a diameter of 4-5 nm, which was an adequate size for the selective uptake by limphs and for the final excretion at the kidney. The dispersity and the MRI visibility of Gd-DTPA-CND particles in human serum were evaluated by the transmission electron microscopy (TEM) and the 1.5T MRI, respectively. It was found that high-contrast imaging could be established by the Gd-DTPA-CND particles, indicating that the Gd-DTPA-CND particles possessed high MRI visibility in distilled water. Furthermore, the Gd-DTPA-CND particles also presented high dispersity and MRI visibility even in human serum, suggesting that the particles could be used intravitally. Therefore, it was concluded that Gd-DTPA-CND particles could be promising MRI contrast agents for the imaging of the lymphatic system through subcutaneous injection.