Highly sensitiveT₁-T₂dual-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 efficientT₁-T₂dual-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,T₁andT₂values of GMIO-2 were measured through a series of turbo spin-echo images and then multi-spin echo sequence, respectively. Based on this,T₁andT₂relaxivities of GMIO-2 were calculated and were the highest (r₁: 1.306 m M^-1s^-1andr₂: 234.5 m M^-1s^-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 excellentT₁-T₂dual-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 aT₁-T₂dual-mode MRI CA.