Nanoshell magnetic resonance imaging contrast agents

Nanocontrast agents have great potential in magnetic resonance (MR) molecular imaging applications for clinical diagnosis. We synthesized Au ₃Cu₁ (gold and copper) nanoshells that showed a promising MR contrast effect. For in vitro MR images, the large proton r₁ relaxivities brightened T₁-weighted images. As for the proton-dephasing effect in T₂, Au₃Cu₁ lightened MR images at the low concentration of 0.125 mg mL^-1 (3.84 × 10^-7 mM), and then the signal continuously decreased as the concentration increased. For in vivo MR imaging, Au₃Cu₁ nanocontrast agents enhanced the contrast of blood vessels and suggested their potential use in MR angiography as blood-pool agents. We propose that (1) the cooperativity originating from the form of the nanoparticles and (2) the large surface area coordinated to water from their porous hollow morphology are important for efficient relaxivity. In a cytotoxicity and animal survival assay, Au₃Cu₁ nanocontrast agents showed a dose-dependent toxic effect: the viability rate of experimental mice reached 83% at a dose of 20 mg kg^-1 and as much as 100% at 2 mg kg^-1.