A Northwestern University study shows that coupling a magnetic resonance imaging (MRI) contrast agent to a nanometer-scale diamond results in dramatically enhanced signal intensity. “The results are a leap and not a small one – it is a game-changing event for sensitivity,” said researcher Thomas J. Meade. “This is an imaging agent on steroids. The complex is far more sensitive than anything else I’ve seen.” Meade, the Eileen Foell Professor in Cancer Research in the Weinberg College of Arts and Sciences and the Feinberg School of Medicine, led the study along with Dean Ho, assistant professor of biomedical engineering and mechanical engineering in the McCormick School of Engineering and Applied Science. Ho previously demonstrated that the nanodiamonds have excellent biocompatibility and can be used for efficient drug delivery. This new work paves the way for the clinical use of nanodiamonds to both deliver therapeutics and to remotely track the activity and location of the drugs. The study, published online by the journal Nano Letters, also is the first published report of nanodiamonds being imaged by MRI technology, to the best of the researchers’ knowledge. The ability to image nanodiamonds in vivo would be useful in biological studies where long-term cellular fate mapping is critical, such as tracking stem cells. MRI uses intravenous contrast agents, such as gadolinium (Gd) to produce detailed images of internal structures in the body. The technique is capable of deep tissue penetration, achieves an efficient level of soft tissue contrast with high spatial and time-related resolution, and does not require ionizing radiation. Meade, Ho and their colleagues developed a gadolinium(III)-nanodiamond complex that, in a series of tests, demonstrated a significant increase in contrast enhancement. They imaged a variety of nanodiamond samples, including ones decorated with various concentrations of Gd(III), undecorated nanodiamonds and water. The intense signal of the Gd(III)-nanodiamond complex was brightest when the Gd(III) level was highest. “Nanodiamonds have been shown to be effective in attracting water molecules to their surface, which can enhance the relaxivity properties of the Gd(III)-nanodiamond complex,” said Ho. “This might explain why these complexes are so bright and such good contrast agents.” “The nanodiamonds are utterly unique among nanoparticles,” Meade added. “A nanodiamond is like a cargo ship — it gives us a nontoxic platform upon which to put different types of drugs and imaging agents.” Nanodiamonds are carbon-based materials approximately 4 to 6 nm in diameter. Each nanodiamond’s surface possesses carboxyl groups that allow a wide spectrum of compounds to be attached to it, not just Gd(III). The biocompatibility of the Gd(III)-nanodiamond complex underscores its clinical relevance. In addition to confirming the improved signal produced by the hybrid, the researchers conducted toxicity studies using various types of cells as biological test beds. They found that the hybrid complex had little effect on cellular viability, affirming its inherent safety and positioning it as a clinically significant nanomaterial. (Other nanodiamond imaging methods, such as fluorescent nanodiamond agents, have limited tissue penetration and are more appropriate for histological applications.) The researchers are exploring the preclinical application of the MRI contrast agent-nanodiamond hybrid in various animal models. With an eye towards optimizing the material, they also are continuing studies of the structure of the Gd(III)-nanodiamond complex. The researchers’ Nano Letters paper, titled “Gd(III)-Nanodiamond Conjugates for MRI Contrast Enhancement,” was published online on Dec. 28, 2009. For more information, visit: http://chemgroups.northwestern.edu/meade