Gadolinum-gold core-shell nanocrystals: Potential contrast agents for molecular MRI with high T1 relaxivity

Gold-coated gadolinium nanocrystals have been synthesized and their relaxivities, R1 and R2, found to be 19.7 and 21.7 s−1 mM−1 respectively at a 9.4 T applied field. R1 is more than 3 times higher than commercial Gd3+ chelate contrast agents on a per Gd atom basis and over 3000 times higher on a per nanocrystal (molecule) basis. Furthermore, the R2/R1 ratio, 1.1, is near ideal for a T1 contrast agent. Colloids of the PVP coated Gd@Au nanocrystals are stable in solution at physiological pH for more than a week. The Au shell protects the Gd from reaction over even in low pH solution. These results indicate that Gd@Au is an exceptionally promising candidate for development as an MRI T1 contrast agent for molecular imaging.