Nanotechnology
Connects Dots
to Disease Detection


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Photograph of several vials of Qdot nanocrystals under black light excitation. Image: Travis Jennings / Wikimedia Commons

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After a 15-year long audition on the scientific stage, quantum dots (QDs) are ready for prime time. They passed their screen test at the 2013 Consumer Electronics Show in Las Vegas with flying colors. Their star turn? A key supporting role in Sony’s forthcoming line of Bravia LCD TVs, featuring a super-sharp, QD-enabled color performance, which earned a CES Best in Show nod from electronics-watching web site TechRadar.

By targeting a mass consumer market in electronics, QD manufacturers may help biomedical engineers target masses of a different and more deadly variety – early signs of cancer cells and tumors. New QD-based detection and diagnostic tools are a quantum leap closer to reality, and just in time to help overcome one of today’s biggest challenges in cancer medicine.

What’s in a Dot?

It turns out there’s a lot inside a tiny quantum dot. They’re essentially colloidal semiconductor nanocrystals engineered to do unusual things to light. All molecules absorb and re-emit light at characteristic wavelengths in the electromagnetic spectrum – that’s how we see color, and how we’ve learned to correlate these effects with physical structure and properties. But scientists have learned how to tune them to specific emission wavelengths based on their size, which can fall somewhere in the range between 10 and 20 nm.

TV picture quality without (left) and with (right) ColorIQ. Image: ColorIQ Facebook Page

 

 

QD Vision (Lexington, MA) makes the dots behind Sony’s new screens. The company says its ColorIQ dots can double the color performance of today’s LCD screens by capturing up to 100% of the National Television System Committee color standard. The ColorIQ optical system comprises a layer of red and green quantum dots placed on an array of blue LED backlights. The LEDs emit blue light while also stimulating the unique, size-dependent properties of the red and green nanoparticles. For non-videophiles, it boils down to redder reds, greener greens, and bluer blues.

Cancer imaging specialists prize QDs for the same reasons. Some want to build better cancer screening equipment to catch cancer signs earlier and more accurately. Others want a better way to understand the complex biochemical marching orders of cancer at the molecular level. On both scales, cancer cells act differently in every patient. To defeat them, scientists have to see them in real time and living color. Quantum dots give off brighter, longer-lasting colors with fewer problems than traditional fluorescent dyes.

QD supplier Invitrogen (Life Technologies, Carlsbad, CA) says its Qdot nanocrystals are based in part on pioneering research at the former Bell Laboratories led by Paul Alivisatos, now director of Lawrence Berkeley National Laboratory, and Moungi Bawendi, now at MIT. Qdot nanocrystals are clusters of semiconducting atoms – usually some mix of cadmium and selenium or telluride. Depending on the desired size of the final structure, the cluster can hold anywhere from a few hundred to a few hundred thousand individual atoms, which are then encased in a semiconducting metal shell and coated with a layer of polymer to achieve a specific optical effect.

Multicolor immunofluorescence imaging with Qdot secondary antibody conjugates. Image: Invitrogen.com

Holes in the Screen

QDs offer just one way to solve one of the rate-limiting problems in the war on cancer. Better screening and detection technologies of all kinds are needed to find earlier signs of more types of cancer, to overcome patient resistance, and to differentiate between dangerous cancers from harmless abnormalities that need no treatment. Several surprising recommendations against routine cancer screenings from public health watchdogs like the U.S. Preventive Services Task Force are confusing patients and physicians alike. Based on USPSTF’s analysis of the medical evidence, it would seem the tools we once viewed as our best defense against cancer may actually be of little value – and often even harmful – to the general population.

But it’s a mechanical problem at heart, and engineers can solve it – possibly with the help of QDs. Bioengineers are developing next-generation imaging hardware, software, and workflows that reveal exactly how cancers form and spread, how an experimental drug affects healthy and diseased cells, and when tumors have been fully eliminated.

Single-molecule analysis is an exciting way to capture and interpret the chemical signals passed between cells on their journey from healthy to malignant, says Tania Vu, associate professor of biomedical engineering at the Knight Cancer Institute at Oregon Health & Science University (Portland). She points to the work of researchers like biomedical engineer Shuming Nie, Ph.D., director of Georgia Institute of Technology/Emory University Cancer Nanotechnology Center, as potentially game changing in the clinical migration of QDs. Among Nie’s QD-powered ideas include some of the first algorithms that translate QD fluorescence data into biological information and also handheld probe that confirms that a surgeon has left no trace of a tumor behind before finishing an operation.

Researchers like Vu believe the timing of QDs’ commercial breakthrough couldn’t be better for cancer researchers. She has spent a decade exploiting QD properties to develop advanced – often stunning – images of healthy and diseased cells and tissues. If commercial sales result in a wider range of cheaper dots on the market, it will help translate this capability into new levels of resolution and precision for commercial cancer screening and diagnostic tools.

Vu is optimistic that her work will soon be available to help patients. Two projects in the works are promising, she says, including one with an affiliate of Roche and another internal collaboration that may still involve an industry partner. “I wouldn’t want to say exactly when, but the near future is very viable,” she says.

Michael MacRae is an independent writer.

If commercial sales result in a wider range of cheaper dots on the market, it will help translate this capability into new levels of resolution and precision for commercial cancer screening and diagnostic tools.

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April 2013

by Michael MacRae, ASME.org