Core-shell NaGdF₄@CaCO₃ nanoparticles for enhanced magnetic resonance/ultrasonic dual-modal imaging via tumor acidic...

For cancer diagnosis, a paramount challenge still exists in the exploring of methods that can precisely discriminate tumor tissues from their surrounding healthy tissues with a high target-to-background signal ratio. Here, we report a NaGdF₄@CaCO₃-PEG core-shell nanoparticle which has the tumor acidic microenvironment enhanced imaging signals of ultrasound and magnetic resonance. Under the acidic conditions, the CaCO₃ shell will gradually dissolve which then facilitate the interaction of NaGdF₄ with the external aqueous environment to enhance water proton relaxation. Meanwhile, the CO₂ bubbles generated by the CaCO₃ dissolvement will generate strong elastic echo for US detection. The core-shell structure of NaGdF₄@CaCO₃-PEG can be observed by TEM, and its composition can be determined by STEM. The acid triggered generation of CO₂ bubbles and the enhancement of MRI signal could be demonstrated in vitro, and the excellent dual-modal magnetic resonance/ultrasonic cancer imaging abilities of NaGdF₄@CaCO₃-PEG could be also proved at the tumor site in vivo. The here described proof-of-concept nanoparticles with pH triggered magnetic resonance/ultrasonic dual-modal imaging enhancement, may serve as a useful guide to develop various molecular imaging strategies for cancer diagnosis in the future.