IEEE Spectrum October, 2016 - 28

oct 2016

North AmericAN

SPectrUm.ieee.orG

Color my world: Researchers at Nanoco Technologies
[opposite page] are working to perfect quantum dots that are free
of cadmium and other toxic heavy metals in hopes that they can be
used in medical treatments. When illuminated with shortwave light,
different size quantum dots fluoresce with different colors.

tures they create are particularly vivid, showing upwards
of 50 percent more color range than the average display.
Their use in TVs also lowers power consumption, because
less of the backlight's energy is absorbed by the color filters in the LCD screen.
One hurdle for this technology has been that quantum dots
typically contain cadmium, a heavy metal that's extremely
toxic. Cadmium plays the role of a group II element here,
often being combined with the group VI element selenium.
Because of environmental concerns, more and more countries are outlawing the use of cadmium in electronic products, which spurred our company to devise quantum dots
that are free of this element as well as other toxic heavy
metals. Along the way, we realized that such cadmium-free
quantum dots might also have important uses in medicine.
Most exciting in this regard is that quantum dots have
several advantages over the organic dyes now employed
during certain cancer surgeries. Of course, quantum dots
also present some special challenges, which we've been
working hard to address.
To undersTand how quanTum doTs might
help improve outcomes for some cancer patients,
you need to know a little about how surgeons treat
this disease. They typically remove both the malignant
tumor and the surrounding lymphatic vessels and nodes,
thus preventing them from carrying the cancer to distant
sites in the body. The more lymph nodes removed in surgery, the lower the risk that the cancer will reach other
organs. But the lymphatic vessels and nodes near the tumor
may be healthy, in which case their removal is certainly

NaNoco TechNologies (2)

The biTs of semic onducTing maTerial
that are lately brightening the colors on television
screens hold a much greater promise-that they
will extend lives. These tiny crystals are far too small to be
seen with the naked eye, measuring just one ten-thousandth
the width of a human hair, which is one reason they're
called quantum dots. When you shine a suitable light on
such a dot, it becomes luminous, emitting a very pure color
that is determined by its size.
My colleagues and I at Nanoco Technologies, in Manchester, England, have been working with a team of researchers led by Sandy MacRobert at University College London
to explore quantum-dot technology for various medical
treatments. While there are many exciting possibilities to
be explored, the most important one we're pursuing aims
to help delineate malignant tumors and the pathways along
which they spread, which could improve the safety and
effectiveness of cancer surgery.
The quantum dots we're discussing are engineered from
a blend of elements drawn from groups III and V, or II and
VI, of the periodic table-elements like cadmium, lead, zinc,
arsenic, indium, tellurium, selenium, sulfur, and phosphorus, which are used in pairs or as alloys. In that way quantum
dots are similar to various optoelectronic devices. When
exposed to a relatively shortwave light source, quantum
dots absorb some of its energy and reemit light of a longer
wavelength (which is to say, a different color), a process
known as fluorescence. The size of the dots can be finely
tuned so that they will give off any color of the spectrum
you might want: The bigger the dot, the longer the wavelength it emits.
The most common commercial use of quantum dots by
far has been in the backlights for LCD television screens,
where they help produce two of the three colors needed.
Blue comes directly from an LED, which illuminates quantum dots that in turn produce red and green light. Because
quantum dots emit very pure colors, the television pic-

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