Gadolinium-Complexed Carboxylated Nanodiamond Particles for Magnetic Resonance Imaging of the Lymphatic System

MRI contrast agents with a size of 3-10 nm are considered to be an effective pathway for selective MR lymphatic imaging. In our previous study, we fabricated nanosized MRI contrast agents (Gd-DTPA-ND) with the condensation of nanodiamond (ND) particles and gadolinium chelates (Gd-DTPA). However, these Gd-DTPA-ND particles formed microscale aggregates in distilled water, exceeding the size required for selective lymphatic MR imaging. In this study, carboxylated nanodiamond (CND) particles were utilized as alternative platforms for condensation with gadolinium complexes. The carboxyl groups introduced by oxidation were expected to induce hydrophilicity with a negative charge on the ND surface, resulting in the high dispersity of gadolinium-complexed CND particles. The fabricated Gd-DTPA-CND particles possessed a hydrodynamic diameter of around 4-5 nm without any signs of aggregation in distilled water and human serum. Furthermore, the T1-weighted image of Gd-DTPA-CND particles in distilled water and human serum presented strong contrast, indicating the excellent MRI visibility of the particles. Therefore, the Gd-DTPA-CND particles can become practical MRI contrast agents for the achievement of selective MR imaging of the lymphatic system.