Quantum dots are used in biomedical research for imaging and sensing, but concerns have been raised about their toxicity because some constituents are heavy metals. In a pilot study, reported online in Nature Nanotechnology this week, quantum dots containing heavy metals were injected into a small number of non-human primates. Although the quantum dots seemed to cause no acute toxicity, chemical analysis revealed that much of the initial dose remained in the liver, spleen and kidneys after 90 days, suggesting that longer-term studies are needed to determine the ultimate fate of these heavy metals and their impact and persistence in primates.

Previous research gives conflicting information on the cytotoxicity of heavy-metal-containing quantum dots: in cell cultures toxicity is demonstrated but in small animals the effect is variable. In this pilot study, Paras N. Prasad and colleagues injected six rhesus macaques with cadmium-selenium, cadmium-sulphur and zinc-sulphur quantum dots that had been encapsulated in phospholipid micelles, at concentrations suitable for imaging techniques.

The results suggest that acute toxicity of these quantum dots in vivo might be minimal, as indicated by the fact that blood and biochemical markers remained within the normal range during the experiment, and histology of major organs after 90 days showed no abnormalities. Further studies will be needed to determine their longer-term effect.