Nanotech News

December 12, 2005

Unmodified Cadmium Telluride Quantum Dots Prove Toxic

Cadmium-based quantum dots, nanoscale semiconductor particles that shine brightly when struck with light, are fast becoming a standard laboratory tool for studying molecular behavior in living cells. Their small size, brightness, stability and ease of chemical modification have also prompted researchers to explore the use of these molecular labels as potential tumor imaging agents.

One concern about their use in vivo, however, has been that the cadmium could cause toxicity, so investigators have developed coating to make the particles biocompatible. Based on research published in the journal Chemistry & Biology, chemists must redouble their efforts to ensure that whatever coating is applied does not degrade until after the quantum dots are excreted from the body. Several studies have shown, for example, that polymer-coated quantum dots can remain in mice for at least four months after administration.

Dusica Maysinger, Ph.D., and her colleagues at McGill University in Montreal, working with Françoise Winnik at the University of Montreal, studied the effects that uncoated cadmium telluride quantum dots have on cells. The investigators added naked quantum dots to human breast cancer cells growing in culture. They then conducted several assays measuring cell viability and found that these quantum dots triggered extensive damage to the cell membrane, mitochondria, and cell nucleus. Overall cell metabolism also decreased in a manner that was directly proportional to the number of quantum dots entering the cell; that is, the more quantum dots in the cell, the greater the decrease in overall metabolism.

Because of the type of damage they observed in their experiments, the investigators suspected that these ill effects were not the result of cadmium toxicity, but rather resulted from the highly reactive surface of the quantum dots. To test this hypothesis, the researchers added a powerful antioxidant to the cell’s growth medium along with the quantum dots, and indeed, the antioxidant prevented all the cellular damage seen in their initial set of experiments.

This work is detailed in a paper titled, “Unmodified cadmium telluride quantum dots induce reactive oxygen species formation leading to multiple organelle damage and cell death.” Investigators from the University of Zagreb, Croatia, also participated in this study. An abstract is available through PubMed.
View abstract.