Semiconductor QDs have been developed as fluorescence tags in biological and medical applications such as in vitro
and in vivo
biological labeling, imaging,1–6
therapeutic carriers and drug delivery.9–13
To avoid QD aggregation, improve water-solubility and biocompatibility, and exert specific surface chemistry for targeting and delivery, various conformations of semiconductor QDs, such as core-shell structure, organic molecule-modified geometry, and functional polymer capped structure have been developed14–16
. Semiconductor QDs are shown to have advantages of efficient luminescence, high photobleaching threshold, flexible surface chemistry, and good water-solubility for biological and medical applications. However, the issues of toxicity and clearance of QDs in bio-systems are of concern,17–24
as these two issues are not fully understood and must be carefully assessed if QDs are to move from scientific curiosity to biomedical application.
Several reports have examined the toxicity and clearance of QDs.8,18–32
One common understanding for toxicity of cadmium-containing semiconductor QDs is that their toxicity is closely related to the concentration of free Cd2+.17,21,22,28,29
Derfus et al
observed that the cytotoxicity of CdTe QDs was correlated to the liberation of free Cd2+.29
and Zhang et al
recently presented similar evidence showing that the cytotoxicity of QDs behaves in a concentration- and size-dependent manner17
. Another common assumption is that surface capping layers of QDs synthesized under different methods may contribute to the level of toxicity following different mechanisms such as oxidation and breakdown of nanostructures.21,22,28
The distribution and damage of QDs to organs are highly variable, and the clearance of QDs in bio-system also varies according to the concentration and structure of QDs.28, 33, 34
In this paper, we assess the toxicity and clearance of semiconductor CdTe and CdHgTe QDs in vitro in human breast and prostate cancer cells and in vivo following subcutaneous injection in mice.