Quantum Dots by Nature

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An early challenge for the team was figuring out how to separate QDs from the biological material that surrounded and obscured them. “It was a learning process to clean off the organic residues. Once you get rid of that, you begin to see the true structure of the material,” says Kiely. “It took many, many months of frustration for our dedicated team of students (Zhou Yang, Leah Spangler, Chris Curran, Robert Dunleavy and Li Lu) to figure out exactly how to do this. Now that we have a much better understanding, we’re starting to accelerate our progress of new materials discovery.”

The researchers’ work was featured on the cover of the July 2015 issue of Green Chemistry. The article suggests that because a single enzyme in the bacteria is responsible for QD generation, the current cell-based model could be scrapped entirely in the future. QDs could be generated with the same enzyme synthesized from yeast or some other easily manipulated bacteria, says Berger. “We have fairly strong evidence for a cell-free process. It’s more cost-effective to use just a purified enzyme,” he says. The team is pursuing an extracellular approach and is poised to scale up its laboratory success into a future manufacturing enterprise.

The researchers hope to establish a manufacturing company that makes inexpensive QDs in an eco-friendly manner. Conventional manufacturing costs $1,000 to $10,000 per gram. A biomanufacturing technique could potentially slash the price by at least a factor of 10, and the team estimates yields on the order of grams per liter from each batch culture, says McIntosh.

Taking a long view, the three colleagues hope that their method could lead to a plethora of future QD applications, such as greener manufacturing of methanol, an eco-friendly fuel that could be used for cars, heating appliances and electricity generation. Water purification and metal recycling are two other possible uses for this technology, because the enzyme makes QDs by isolating heavy metals from water.

“We also want to create many different types of functional materials and make large-scale functional materials as well as individual quantum dots,” says McIntosh. He imagines developing a process by which quantum dots arrange themselves into macrostructures, the way nature grows a mollusk shell out of individual inorganic nanoparticles. “If we someday get to macroscale, if we’re able to make more of the material and control how it’s structured while maintaining its core functionality, we could potentially get a solar cell to assemble itself with quantum dots. That would be incredible.” 



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