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

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.