Gadolinium Functionalized Carbon Dot Complexes for Dual-Modal Imaging: Structure, Performance, and Applications

Gadolinium functionalized carbon dot complexes (Gd-CDs) have both the fluorescent properties of carbon dots and the magnetic characteristics of gadolinium ions, exhibiting excellent biocompatibility, high spatial resolution, high sensitivity, and deep tissue penetration in bioimaging. As fluorescence (FL) and magnetic resonance imaging (MRI) probes, Gd-CDs have attracted significant attention in dual-modal biological imaging. This review summarizes recent advances in Gd-CDs, focusing on their structure, optical and magnetic properties, and applications in dual-modal imaging. First, according to the different existing forms of gadolinium in carbon dots, the structures of Gd-CDs are categorized into chelation, electrostatic interaction, and encapsulation. Second, the mechanisms and performances of Gd-CDs in dual-modal imaging are introduced in detail. The reported Gd-CDs have a maximum quantum yield of 69.86%, with a fluorescence emission wavelength reaching up to 625 nm, and the optimum longitudinal and transverse relaxivity rates are 35.39 and 115.6 mM^-1 s^-1, respectively, showing excellent FL/MRI capacities. Subsequently, the progress in their applications in dual-modal cellular imaging, in vivo imaging, and integrated cancer diagnosis and therapy is reviewed. Finally, the challenges and issues faced by Gd-CDs in their development are summarized, providing new insights for their controlled synthesis and widespread application in the biomedical field of dual-modal imaging.