High R1 Relaxivity Sub-5 Nm Suprasmall Iron Oxide Nanoparticles (SSIOs) as Intravascular T1-Weighted MRI and Cell Tracking Contrast Agents

Jing Huang¹, Liya Wang¹, Hui Mao¹

Superparamagnetic iron oxide nanoparticles (SPIOs) have been widely used as MRI contrast agents both in clinical applications (e.g. liver, lymph nodes imaging) and preclinical models (e.g. cell tracking, molecular imaging). Currently, most SPIOs are fabricated with size larger than 5 nm, therefore exhibit predominant shortening effect on T2, causing signal void in T2-weighted MRI. Here we report a new class of high r1 relaxivity, sub-5 nm, suprasmall iron oxide nanoparticles (sSIOs, ~3.5 nm) as intravascular T1-weighted MRI contrast agents, providing reverse T2 contrast and T1-T2 contrast switch, when taken up by cells and liver, or between labeled and lysed cells.