Gadolinium-Incorporated Carbon Nanodots for <i>T</i>₁‑Weighted Magnetic Resonance Imaging

The
design and development of contrast agents for magnetic resonance
imaging (MRI) with improved chemical stability and higher contrasting
capability for clinical translation compared to conventional contrast
agents are still of great interest. In this study, a facile and universal
approach was explored for controllable functionalization of red-emissive
carbon nanodots (RCNDs) with diethylenetriaminepentaacetic anhydride
(DTPA) for chelation of gadolinium. A series of accurate characterizations
were used to control each step of the synthesis. The functionalization
did not alter the band gap of the carbon nanodots, preserving their
inherent far-red fluorescence. The as-prepared RCND-DTPA-Gd displayed
a high colloidal stability with negligible Gd leakage. The nanodots
also showed a better magnetic resonance relaxivity than commercial
MRI agents. RCND-DTPA-Gd had good biocompatibility in vivo even at high doses. The systemically injected RCND-DTPA-Gd were
found to be efficiently excreted through the renal route, a feature
that further minimizes the potential toxicity risks. All these properties
suggest that carbon nanodots can be well designed as efficient carriers
of Gd, resulting in potential clinical tools as dual MRI/fluorescence
functional probes for imaging applications. The approach described
here could pave the pathway to a flexible strategy for the controllable
functionalization of small-sized nanoparticles including carbon dots,
rendering them more versatile. This work is expected to promote the
future translation of carbon nanodots into clinical trials.