Highly sensitive T 1–T 2 dual-mode MRI probe based on ultra-small gadolinium oxide-decorated iron oxide nanocrystals

Single-mode magnetic resonance imaging (MRI) contrast agents (CAs) in clinical settings are easily disturbed by calcification, bleeding, and adipose signals, which result in inaccurate diagnoses. In this study, we developed a highly efficient T1–T2 dual-mode MRI CA using an ultra-small gadolinium oxide-decorated magnetic iron oxide nanocrystal (GMIO). The gadolinium element could effectively alter the magnetic properties of the GMIO from soft-ferromagnetism to superparamagnetism. In addition, when the Gd/Fe ratio was 15% (designated as GMIO-2), the GMIO-2 possessed the best superparamagnetism and highest magnetism. Subsequently, T1 and T2 values of GMIO-2 were measured through a series of turbo spin-echo images and then multi-spin echo sequence, respectively. Based on this, T1 and T2 relaxivities of GMIO-2 were calculated and were the highest (r1: 1.306 m M−1 s−1 and r2: 234.5 m M−1 s−1) when compared to other groups. The cytotoxicity of GMIO-2 was negligible under a wide range of dosages, thus exhibiting excellent cell biocompatibility. Moreover, GMIO-2 could quickly diffuse into cells, leading to its effective accumulation. The systemic delivery of GMIO-2 resulted in an excellent T1–T2 dual-mode MRI contrast effect in kidneys, which is expected to improve the diagnosis of kidney lesions. Therefore, this work provides a promising candidate for the development of a T1–T2 dual-mode MRI CA.