Carbon-based nanostructures, such as fullerenes and carbon nanotubes, have received much attention as potential drug carriers. However, researchers are still unsure as to how biocompatible these materials are. Moreover, carbon nanotubes are not soluble in water, which further limits their widespread use.

This is where nanodiamonds come in: they are non-toxic and water soluble, and do not cause cell inflammation, unlike other commonly employed drug-delivery systems. Inflammation is a serious matter and can predispose a patient to further cancer, block the activity of anti-cancer drugs and even promote tumor growth.

"There are a lot of materials that can deliver drugs well, but we need to look at what happens after drug delivery," explained team leader Dean Ho. "Nanodiamonds are highly ordered structures, which cells like. If they didn't cells would become inflamed."

The new system could allow for more sophisticated ways of targeting cancer cells while leaving healthy cells intact.

Ho and colleagues started out with single nanodiamonds that measure just 2 nm across. The researchers then produced clusters of nanodiamonds, ranging from 50 to 100 nm in diameter. An anti-cancer drug loaded onto the surface of the cluster only became active when the cluster reached its target, where it then broke apart and slowly released the drug.

"The nanodiamond cluster provides a powerful release in a localized place – an effective but less toxic delivery method," said team member Eric Pierstorff. Because the clusters have a large surface area, they can carry nearly five times more of a drug than conventional materials. Such materials, including liposomes and polymersomes, which are essentially hollow spheres loaded with an active drug, kill any cells, even healthy ones, on their way to a target cancer cell. Nanodiamonds are also very stable, safe and can be further functionalized for better targeting.

Ho and co-workers have already shown that they can successfully load doxorubicin onto the nanodiamond clusters, which then efficiently ferry the drug inside cancer cells. The researchers also demonstrated that the clusters did not cause inflammation or cell death by analysing the genes associated with these effects. No toxicity or long-term inflation was found and cells continued to grow well in the presence of nanodiamonds.

The work was reported in Nano Letters.