Subnanometer ultra-thin magnetic nanosheets for highly sensitive magnetic resonance angiography

Clinical magnetic resonance contrast agents are currently confronted with challenges such as low relaxation efficiency and elevated biological toxicity, necessitating the urgent development of effective and safe alternatives. In this study, we successfully synthesized unique two-dimensional Gd-doped ZnO nanosheets (GdZn) with subnanometer thickness and elucidated their formation mechanism through a chloride ion-assisted cluster coassembly process. When compared to commercial magnetic resonance contrast agents like Gd-DTPA, the sodium citrate-modified GdZn nanosheets (GdZn-SC) exhibited an exceptionally high r1 value, approximately 6.77 times that of Gd-DTPA, primarily attributed to their ultrathin subnanometer structure, which maximizes exposure of paramagnetic metal ions in the GdZn nanosheets for interaction with water molecules. Furthermore, experimental results demonstrated that ultraviolet light significantly enhanced its r1 (about 1.36 times greater than prior to UV exposure), aligning with the characteristics of photoinduced superhydrophilic-assisted paramagnetic relaxation enhancement (PISA-PRE). In vivo imaging experiments along with metabolic and biotoxicity assessments indicated that GdZn-SC nanosheets represent a highly effective, safe, and promising class of blood pool magnetic resonance contrast agents suitable for contrast-enhanced magnetic resonance angiography (CEMRA) and vascular disease diagnosis.