Tubes filled with quantum dots, which emit many different crisp, dramatic colors under LED lights making them desirable for use in flat-screen displays and medical imaging devices
MAY 5, 2016
*** Re-Post from NY Times
CHRISTA NEU / LEHIGH UNIVERSITY
Over the past few years, screen manufacturers have become obsessed with the potential of tiny crystals known as quantum dots.
The idea is that a quantum dot television or cellphone may offer sharper and brighter images for less money. There was talk that Apple would release an iMac with a quantum dot screen last year.
But then the company switched course, declaring that the existing process for making these little crystals was too toxic to the environment. Samsung offers its SUHD TV with environmentally friendlier quantum dot technology, but it’s not cheap.
In a study published in Proceedings of the National Academy of Sciences last week, five chemical engineers at Lehigh University outline a simpler and more environmentally friendly way to create the dots: Feed some metal to a single enzyme extracted from bacteria. The colorful vials, pictured above, are filled with the little dots grown in a lab at Lehigh through this cost-effective method.
Under LED lights, the little crystals, which can generate both electricity and colored light, glow like plastic pegs on a Lite-Brite screen.
Bryan Berger, a co-author of the study, stumbled across this alternative for creating the little dots through an unintended sequence of events. It began when an alarmed hospital staff in Pennsylvania discovered a superbug growing on metal surfaces in 2011.
Doctors and nurses were worried: Stenotrophomonas maltophila, or steno, as the bacteria is called, can potentially cause bad infections in immune-compromised patients, and few antibiotics can kill it.
So they asked Dr. Berger, a chemical engineer at nearby Lehigh, to find out why the bacteria seemed to thrive on metal.
What Dr. Berger found surprised him. The microbe appeared to be taking in electrical charges, presumably from the metal surfaces, and spitting out clusters of tiny, metallic particles.
Dr. Berger did not know how to halt the superbug, but what he saw sparked his imagination. Could this same bacteria that was spitting out metal be re-engineered as a mini-crystal-generating machine?
Inside glassware under ultraviolet light, quantum dots glow in every spectrum of the rainbow. A new way of creating them may make televisions and cellphones better and cheaper.
The answer was yes.
“As an engineer, it’s extremely exciting, but as a medical scientist, it’s extremely scary,” Dr. Berger said.
He and his colleagues found that within a few minutes of feeding the metal cadmium to the steno bacteria — bam — they had created quantum dots.
They published those findings last year. The problem was that they were using a potentially infectious bug to create the dots. What’s significant about the new study is that Dr. Berger and his colleagues Steve McIntosh and Chris Kiely discovered that they didn’t need the bacteria after all; they could make the dots with a single enzyme inside it.
Quantum dot screens are still a long way from becoming as commonplace as LED screens because they have been expensive and messy to make.
Existing methods can require temperatures as high as 300 degrees Celsius, or 572 degrees Fahrenheit; oily organic solvents that can cause pollution; and costly facilities to make it all happen.
Dr. Berger and his colleagues created their multisize nanocrystals with one enzyme, in water at room temperature. It’s safer, more environmentally friendly and much cheaper than previous approaches, they say. It’s also possible to control the size of the crystals, which determines the color of their light, as you can see above.
Does this mean that sometime soon quantum dot TVs will become much more affordable?
Warren Chan, a biomedical engineer at the University of Toronto who has been synthesizing quantum dots for decades and was not involved in the study, said that’s unlikely with these particular dots.
While he agreed that safer and cheaper production is ideal, these easy-to-make dots aren’t going to be as crisp or as bright as the ones made with previous processes, he said. That means that while they may address Apple’s concerns about toxicity, they won’t meet its other needs — just yet.
But they could be helpful in other ways. Quantum dots are already being developed in medical imaging to tag tumors and identify diseases, and are being closely watched by manufacturers of green energy, for their potential to boost the efficiency of solar cells.
These new dots, if they can be engineered to be even brighter, may have applications there. But that’s a big if.
So what happened at the hospital? Dr. Berger is still trying to figure out how to prevent the superbug’s ability to colonize metal surfaces.
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