IEEE Spectrum October, 2016 - 31

suit. These cadmium-free quantum dots are attractive for
making displays, because they help them conform to various environmental regulations. The first TV sets to use
cadmium-free quantum dots, such as Samsung's SUHD TV,
have just recently appeared on store shelves. But there's
an even greater payoff coming: While definitive tests have
yet to be done, my colleagues and I believe that modified
versions of these cadmium-free quantum dots are likely to
be safe for clinical use inside the human body.
In addition to eliminating the heavy metals, researchers
at our company have developed a special polymer coating to render the dots biocompatible, meaning that they
are not likely to engender inflammation or any other sort
of immunological response. Nanoco's research partners
at University College London have used these dots successfully in surgery to remove tumors and surrounding
tissue from mice, with no detectable toxic side effects in
the animals.
Of course, even if these quantum dots prove perfectly
safe, it will take a long time to determine just how much
of an advance they represent over conventional dyes and
radioactive tracers. It seems reasonable to suppose that
they will improve outcomes in cancer surgery, but clinical
trials will have to be carried out to determine whether surgeons actually remove more cancerous tissue with quantum dots guiding their decisions, whether that lowers the
risk that the cancer will spread, and whether there will be
less need for repeat surgeries.
In addition to delineating tumors, the quantum dots may
have other important uses in cancer treatment. In particular, physicians may someday be able to use quantum
dots to destroy cancerous tumors in place. That's because
tumors typically absorb and accumulate nanoparticles
faster than do normal healthy tissues, a phenomenon
called enhanced permeability and retention. So quantum dots could, in principle, also be used as an integral
part of chemotherapeutic drugs that are preferentially
absorbed by a tumor.
Another exciting possibility involves the application of
quantum dots to something called photodynamic therapy,
which can be used instead of surgery to treat cancer by
killing malignant cells through exposure to light. For this,
physicians first inject special sensitizing drugs, which are
preferentially taken up by cancerous tissues. When light is
shone on the tumor, the sensitizing molecules absorb energy
from the light and cause a toxic form of oxygen to be produced, which then kills the surrounding cancerous cells.
Special quantum dots could be created to help with such
procedures. The dots would serve to transfer energy from
the light to attached sensitizing molecules, thus enhancing the ability of traditional photodynamic-therapy drugs
to kill malignant cells.
illustration by

David Schneider

canc er TreaT menT is jusT one of many
promising applications for quantum dots in medicine, but the question that is holding back all this
research is whether it's safe to use them inside a human
being. Injecting substances into the body is never without
risk, and quantum dots have long been a worry in that
regard. But the elimination of toxic heavy metals and the
use of biocompatible coatings should go a long way in alleviating concerns.
The most likely problem posed by the quantum dots my
colleagues and I have been investigating is allergic reaction,
an all-too-common phenomenon in medicine. Indeed, an
organic dye commonly used now for cancer surgery elicits
dangerous allergic responses in 1 to 3 percent of patients.
We won't know how allergenic our quantum dots are until
we conduct human trials, which are probably two to three
years away yet. But if all goes as we hope, the new dots won't
prove any worse in this regard than today's organic dyes. If
so, nontoxic quantum dots could begin helping to extend
the lives of cancer patients perhaps just a few short years
after that. It will be a triumph well worth remembering while
enjoying the especially vivid picture on the television you
have at home, where the same fundamental technology will
by that time probably be at work. ■

spheres of influenCe: Quantum dots are composed of
at least two types of atoms [red and blue], typically arranged
in a face-centered cubic lattice, where each atom's nearest
neighbors are four atoms of the opposite type positioned
at the vertices of a regular tetrahedron. The most common
form of quantum dot is composed of cadmium and selenium,
but concern over toxic effects has prompted researchers to
replace those with more benign elements. For medical use in
the body, quantum dots must also be given a biocompatible
coating [pale yellow].
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North AmericAN

oct 2016

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Table of Contents for the Digital Edition of IEEE Spectrum October, 2016