Tests with this nanoscale egg, which has a hard cobalt shell surrounding a “yolk” of platinum and iron, show that it is seven times more toxic than the anticancer agent cisplatin to cancer cells.

Reporting its work in the Journal of the American Chemical Society, a team of investigators led by Bing Xu, describes the methods used to make these novel nanoparticles. The researchers start by synthesising cobalt sulphide nanoparticles, which naturally form a hollow shell structure, in the presence of nanoparticles made of iron and platinum. Transmission electron microscopy (TEM) and x-ray spectroscopy studies of these nanoparticles indicate that the resulting structures have a porous crystalline shell of cobalt sulphide surrounding nanocrystals of iron/platinum. The pores in the outer shell are large enough for water to access the interior of the nanoparticle.

When added to cultured human tumour cells, these nanoparticles had an immediate effect on cell viability. After 72 hours, all tumour cells exposed to the nanoparticles died. Again using TEM, the investigators showed that the cobalt sulphide shell remained intact after the nanoparticles were taken up by tumour cells. By themselves, hollow cobalt sulphide nanoparticles - the egg without the yolk - were not toxic to cultured human cancer cells.

The researchers hypothesise that cells take up the nanoparticles via a process known as endocytosis. As a result of endocytosis, the nanoparticles would end up in small intracellular compartments that are acidic. Under those conditions, the iron/platinum nanocrystals would dissolve, allowing the nanoscale eggs to release platinum into the cancer cells. (Source: National Cancer Institute).