Primate Study Deems QDs Nontoxic — at Least for Short Term

Cadmium-selenide quantum dots are nontoxic to primates over a one-year period, a new study has found. The dots could hold great promise as tools for treating and detecting diseases such as cancer through nanomedicine.

The nanosize luminescent crystals typically are made from metals such as cadmium or zinc and glow brightly in different colors. Medical researchers are eyeing the crystals for use in image-guided surgery, light-activated therapies and sensitive diagnostic tests. Among the most studied, cadmium-selenide quantum dots are suitable not only for medical applications, but also as components for LEDs, quantum computers and solar cells.

A solution of cadmium-selenide quantum dots glows orange under ultraviolet light. This luminescence forms the basis for their use in bioimaging. (Images: University at Buffalo)

The toxicity study, completed by the University at Buffalo (UB), the Chinese PLA General Hospital, China's ChangChun University of Science and Technology and Singapore’s Nanyang Technological University, aimed to address concerns of health professionals who worry that quantum dots might be dangerous to humans.

Four rhesus monkeys were injected with cadmium-selenide quantum dots in the study. They remained in normal health for more than 90 days — their blood and biochemical markers were tested and their organs developed no abnormalities. They also not lose weight. Two monkeys were then observed for an additional year and also showed no signs of illness.

“This is the first study that uses primates as animal models for in vivo studies with quantum dots,” said Paras Prasad, a UB professor of chemistry and medicine. “So far, such toxicity studies have focused only on mice and rats, but humans are very different from mice. More studies using animal models that are closer to humans are necessary.”

Transmission electron microscopy shows clusters of quantum dots. In application, each cluster is encased in a single capsule with an average size near 50 nm.

More research will need to be done to determine the nanocrystals’ long-term effects in primates; most of the potentially toxic cadmium from the quantum dots stayed in the liver, spleen and kidneys of the animals studied over the 90-day period. This is a serious concern that warrants further investigation, said Ken Tye Yong, a Nanyang Technological University assistant professor.

As such, the scientists believe that cadmium-selenide quantum dots might be best used only in a limited capacity, such as image-guided surgery, where a single dose of the dots could be used to identify a tumor or other target area.

The research appeared online May 20 in Nature Nanotechnology.

For more information, visit: www.buffalo.edu