Nanomedicine: Quantum dots appear safe in pioneering study on primates

May 20, 2012, University at Buffalo
Transmission electron microscopy shows clusters of quantum dots. In application, each cluster is encased in a single capsule with an average size near 50 nanometers. Credit: University at Buffalo

A pioneering study to gauge the toxicity of quantum dots in primates has found the tiny crystals to be safe over a one-year period, a hopeful outcome for doctors and scientists seeking new ways to battle diseases like cancer through nanomedicine.

The research, which will appear on May 20 in Nature Nanotechnology online, is likely the first to test the safety of quantum dots in .

In the study, scientists found that four injected with cadmium-selenide quantum dots remained in normal health over 90 days. Blood and stayed in typical ranges, and major organs developed no abnormalities. The animals didn't lose weight.

Two monkeys observed for an additional year also showed no signs of illness.

Quantum dots are tiny luminescent crystals that glow brightly in different colors. Medical researchers are eyeing the crystals for use in image-guided surgery, light-activated therapies and sensitive diagnostic tests. Cadmium selenide quantum dots are among the most studied, with potential applications not only in medicine, but as components of , quantum computers, light-emitting diodes and more.

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

The new toxicity study -- completed by the University at Buffalo, the Chinese PLA General Hospital, China's ChangChun University of Science and Technology, and Singapore's Nanyang Technological University -- begins to address the concern of health professionals who worry that quantum dots may be dangerous to humans.

The authors caution, however, that more research is needed 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 the first study that uses primates as animal models for in vivo studies with quantum dots," said paper coauthor Paras Prasad, UB professor of chemistry and medicine, and executive director of UB's Institute for Lasers, Photonics and Biophotonics (ILPB). "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."

The cadmium build-up, in particular, is a serious concern that warrants further investigation, said Ken-Tye Yong, a Nanyang Technological University assistant professor who began working with Prasad on the study as a postdoctoral researcher at UB.

Because of that concern, the best in-vivo applications for quantum dots in medicine may be the ones that use the crystals in a limited capacity, said Mark Swihart, a third coauthor and a UB professor of chemical and biological engineering. Image-guided surgery, which could involve a single dose of to identify a tumor or other target area, falls into this category.

Explore further: Cadmium selenide quantum dots degrade in soil, releasing their toxic guts

More information: DOI: 10.1038/nnano.2012.74

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not rated yet May 20, 2012
A yearbdoesn't sound like much.

E.g. clinical studies for new drugs are tested on thousands of people for a up to 5 years in the final phase.

Observing some monkeys for 90 days and just two for a year after that is not enough. This really needs to go into another, serious, round of testing.
1 / 5 (1) May 20, 2012
here here. i've been concerned about this for some time (on occasion) and haven't ever looked into it.
we don't want AI strangling us from the insides...
1 / 5 (1) May 20, 2012
Unbelievable. No level of cadmium is safe, and it cannot be chelated.

A true advance of science does not expose humans to toxins.
not rated yet May 20, 2012

This is clearly some fluff that will be utilised by the nano-industry to counter any/all claims of harmfulness or toxicity of nanomaterials --wether this was the intention of the researchers or not.

No observation of gross effect is not the same as no effect. Plenty of organisms can function normally over long periods with anywhere from mild to severe impairment of any one of a number of vital systems --but this doesn't mean they are free from harm or disease.

No, until every molecule of these dots can be tagged, and all the implanted material accounted for(wether held internally or excreted), for the life of the subject animal --then no valid conclusions can be made regarding the ultimate toxicity or other harmfulness of these materials.

Further, any effects or lack thereof will only apply to this specific substance --as soon as the composition is modified, the possibility of effect is, too-- and thus, no generalizations as to safety can be made, realistically speaking.

5 / 5 (1) May 20, 2012

From the abstract of the actual article at: http://www.nature....74.html (Can we please allow HTML tags?)

However, chemical analysis revealed that most of the initial dose of cadmium remained in the liver, spleen and kidneys after 90 days. This means that the breakdown and clearance of quantum dots is quite slow, suggesting that longer-term studies will be required to determine the ultimate fate of these heavy metals and the impact of their persistence in primates.

You may unfortunately be correct about business touting this as "proof" that nanotechnology is safe; but the researchers certainly are not claiming that. They are simply claiming that a very limited study showed no adverse effects and I'm sure are hoping for further funding to run long term studies. Progress is still progress and I'm happy to see it.
not rated yet May 21, 2012
Unbelievable. No level of cadmium is safe, and it cannot be chelated.

EDTA can be used as a chelating agent, amongst other things.


It is important to mention that the article does point out that long-term low level doses of cadmium is not expelled by chelation.

This could suggest that the use of a chelating agent given at the time of quantum dot administration or part of some predetermined schedule, could be useful to chelate cadmium ions, consequently reducing toxicity.
not rated yet May 21, 2012
This could suggest that the use of a chelating agent given at the time of quantum dot administration or part of some predetermined schedule, could be useful to chelate cadmium ions, consequently reducing toxicity.

Chelating the quantunm dots would defeat their purpose.

Getting them out of the kidneys and liver will be tricky. I can see where quantum dots could be enormously useful, but unless they are able to pair quantum dots with an easily accessible connection point (i.e.something another medication can bind to which could then be designed to so as to be easily expeled from the body - draging the quantum dt with it in the process) this is a problem.
not rated yet May 21, 2012
Chelating the quantunm dots would defeat their purpose.

I'm assuming the quantum dots themselves would not be chelated, only once they degrade and produce a cadmium ion would there be some interaction. Based on the article though, it would seem that would take some time which, in effect, would mean a chelating agent is out of the question (I guess I proved my previous statement wrong).

Instead of interaction between a quantum dot and a carrier molecule, adding quantum dots to some protein with a selective enough domain(s)/receptor(s) might solve this as well; active form is administered, another drug(s) deactivates and allows expulsion. I imagine preserving the properties of a quantum dot attached to a protein would be extremely difficult though, maybe even impossible?

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