Diamonds are among the hardest substances on Earth. Probably because of their hardness, they are impervious to biological materials. Nanodiamonds, diamond particles no bigger than six nanometers (recall that a nanometer is 1 hundred thousandth of the thickness of human hair), can be released in the human bloodstream and are biologically neutral. So why would anyone want to release nanodiamonds into the bloodstream? As it turns out, lots of reasons; but for the purposes of research at Northwestern University (Chicago, USA), the nanodiamonds can be teamed with a substance called gadolinium(III) to turn dull, difficult to read MRI scans into scintillating, high contrast, feature popping images.
Magnetic resonance imaging (MRI), especially if you watch the med shows, is a well known, usually non-harmful method for obtaining images of the internal workings of the human (or other) body. It’s a fairly new technology (circa 1974-75) that uses powerful magnetic fields to penetrate living tissue, and relies on some kind of metallic substance to ‘spin’ the magnetism so that an image can be formed. That substance–the contrast agent–is usually an organic (chelated) form of gadolinium, a rare-earth metal element, which is usually introduced into the body intravenously. Gadolinium makes for good contrast in the MRI image, but not great.
The researchers reasoned that teaming gadolinium with something else, might increase the (here comes a doozy word) relaxivity. (In an un-cracked nutshell: Relaxivity occurs when the protons of water, which have been made to spin by magnetic fields, lose their spin (relax) and return to an equilibrium state.) The rate at which relaxivity occurs (the relaxation time) determines how much contrast an MRI image can develop. The faster (relaxivity), the better. The gadolinium complex used in the research, which included the nanodiamonds, was found to increase the relaxivity not just a little, but a lot – a ten-fold increase. The resulting improvement in MRI contrast and image clarity is dramatic.
“The results are a leap and not a small one — it is a game-changing event for sensitivity,” said Thomas J. Meade, the Eileen Foell Professor in Cancer Research in the Weinberg College of Arts and Sciences and the Feinberg School of Medicine. “This is an imaging agent on steroids. The complex is far more sensitive than anything else I’ve seen.”
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 fibroblasts and HeLa cells as biological testbeds.
They found little impact of the hybrid complex on cellular viability, affirming the complex’s inherent safety and positioning it as a clinically significant nanomaterial.
It can be said that the primary use of nanodiamonds will be to deliver drugs to targeted areas in the body. The surface of nanodiamonds (diamond being an almost pure carbon allotrope) readily contains carboxyl groups (active organic compounds of carbonyl (CO) and hydroxyl (OH)), which makes it relatively easy to attach drugs, markers, dyes and other organic material. The attachment of an organic form of gadolinium is really just one example.