Title: Cation Exchange Strategy to Construct a Targeting Nanoprobe for Enhanced Positive MR Imaging Capability
Abstract: Abstract Background: Excellent imaging performance and good biocompatibility of contrast agents are considered as prerequisites for accurate tumor diagnosis and treatment. Results: Herein, a novel imaging nanoprobe with actively targeting performance based on ultrasmall paramagnetic iron oxide (USPIO) was constructed by a facile cation exchange strategy followed by conjugation with transferrin (Tf). The stable gadolinium (Gd 3+ ) chelation endows the nanoparticles (NPs) with a low value of r 2 /r 1 (1.28) and relatively high r 1 value of 3.2 mM -1 s -1 , enabling their use in T 1 -weighted positive MR imaging. Conclusion: This constructed transferrin modified gadolinium-iron chelate nanoprobe, named as TUG, shows high biocompatibility within a given dose range. More importantly, compared with clinically used Gd-based small molecule contrast agents, the obtained TUG can be more engulfed by breast cancer cells, showing much enhanced T 1 -weighted positive MR imaging in either subcutaneous or in situ tumor models of breast cancer. This novel nanoprobe holds enormous promise to be utilized as a targeting contrast agent with high efficacy for T 1 -weighted positive MR imaging.