Lehigh University: First single-Enzyme Method to mass-produce Quantum Dots: significantly quicker, cheaper and greener production method

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Tubes filled with quantum dots produced in the Lehigh University lab. Credit: Christa Neu/Lehigh University Communications + Public Affairs

Quantum dots (QDs) are semiconducting nanocrystals prized for their optical and electronic properties. The brilliant, pure colors produced by QDs when stimulated with ultraviolet light are ideal for use in flat screen displays, medical imaging devices, solar panels and LEDs. One obstacle to mass production and widespread use of these wonder particles is the difficulty and expense associated with current chemical manufacturing methods that often requiring heat, high pressure and toxic solvents.

But now three Lehigh University engineers have successfully demonstrated the first precisely controlled, biological way to manufacture quantum dots using a single-enzyme, paving the way for a significantly quicker, cheaper and greener production method.

The Lehigh team— Bryan Berger, Class of 1961 Associate Professor, Chemical and Biomolecular Engineering; Chris Kiely, Harold B. Chambers Senior Professor, Materials Science and Engineering and Steven McIntosh, Class of 1961 Associate Professor, Chemical and Biomolecular Engineering, along with Ph.D. candidate Li Lu and undergraduate Robert Dunleavy—have detailed their findings in an article called “Single Enzyme Biomineralization of Cadmium Sulfide Nanocrystals with Controlled Optical Properties” published in theProceedings of the National Academy of Sciences.

“The beauty of a biological approach is that it cuts down on the production needs, environmental burden and production time quite a lot,” says Berger.

In July of last year, the team’s work was featured on the cover of Green Chemistry describing their use of “directed evolution” to alter a bacterial strain called Stenotophomonas maltophilia to selectively produce cadmium sulphide QDs. Because they discovered that a single enzyme produced by the bacteria is responsible for QD generation, the cell-based production route was scrapped entirely. The cadmium sulphide QDs, as they have now shown in the PNAS article, can be generated with the same enzyme synthesized from other easily engineered bacteria such as E. coli.

“We have evolved the enzyme beyond what nature intended,” says Berger, engineering it to not only make the crystal structure of the QDs, but control their size. The result is the ability to uniformly produce quantum dots that emit any particular color they choose—the very characteristic that makes this material attractive for many applications.

Industrial processes take many hours to grow the nanocrystals, which then need to undergo additional processing and purifying steps. Biosynthesis, on the other hand, takes minutes to a few hours maximum to make the full range of quantum dot sizes (about 2 to 3 nanometers) in a continuous, environmentally friendly process at ambient conditions in water that needs no post-processing steps to harvest the final, water-soluble product.

Perfecting the methodology to structurally analyze individual nanoparticles required a highly sophisticated Scanning Transmission Electron Microscope (STEM). Lehigh’s Electron Microscopy and Nanofabrication Facility was able to provide a $4.5 million state-of-the-art instrument that allowed the researchers to examine the structure and composition of each QD, which is only composed of tens to hundreds of atoms.

“Even with this new microscope, we’re pushing the limits of what can be done,” says Kiely.

The instrument scans an ultra-fine electron beam across a field of QDs. The atoms scatter the electrons in the beam, producing a kind of shadow image on a fluorescent screen, akin to the way an object blocking light produces a shadow on the wall. A digital camera records the highly magnified atomic resolution image of the nanocrystal for analysis.

The team is poised to scale-up its laboratory success into a manufacturing enterprise making inexpensive QDs in an eco-friendly manner. Conventional chemical 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 will 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.

“We 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 individual quantum dots arrange themselves into macrostructures, the way nature grows a mollusk shell out of individual inorganic nanoparticles or humans grow artificial tissue in a lab.

“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 .”

Explore further: Robust approach for preparing polymer-coated quantum dots

More information: Robert Dunleavy et al, Single-enzyme biomineralization of cadmium sulfide nanocrystals with controlled optical properties, Proceedings of the National Academy of Sciences (2016).DOI: 10.1073/pnas.1523633113


The Curious Tale of Quantum Dots – “Comimg to a Screen Near You … Soon?”

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


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.

Lehigh University: Innovators shine at international conference

Lehigh scientists and engineers won three National Innovation Awards recently at the TechConnect 2015 World Innovation Conference and National Innovation Showcase held in Washington, D.C.

The awards were for a nanoscale device that captures tumor cells in the blood, a bioengineered enzyme that scrubs microbial biofilms, and a safe, efficient chemical reagent that is stable at room temperature.

Lehigh’s TechConnect initiative was led by the Office of Technology Transfer (OTT) which manages, protects and licenses intellectual property (IP) developed at Lehigh. Yatin Karpe, associate director of the OTT, spearheaded the Lehigh effort and is pursuing IP protection and commercialization for the innovations.

The P.C. Rossin College of Engineering and Applied Science, led by former interim Dean Daniel Lopresti, and the Office of Economic Engagement, led by assistant vice president Cameron McCoy, supported Lehigh’s third-straight appearance at the annual conference.

The three National Innovation Awards were chosen through an industry review of the top 20 percent of annually submitted technologies and based on the potential positive impact the technology would have on industry.

This is the third year in a row that Lehigh has won Innovation Awards. No institution received more than three in 2015.

Lehigh’s National Innovation Awardees were:

•    Yaling Liu, assistant professor of mechanical engineering and mechanics and a member of the bioengineering program, has developed a tiny device that can capture tumor cells circulating in the blood and can potentially indicate disease type, as well as genetic and protein markers that may provide potential treatment options.

•    Bryan Berger, assistant professor of chemical and biomolecular engineering, hopes to improve food safety and keep medical devices clean with an enzyme he’s developed that attacks biofilms.

•    David Vicic, professor and department chair of chemistry, has created a new chemical reagent that is stable at room temperature, potentially eliminating the use of traditional hazardous regents.

TechConnect is one of the largest multi-sector gatherings in the world of technology intellectual property, technology ventures, industrial partners and investors. The event brings together the world’s top technology transfer offices, companies and investment firms to identify the most promising technologies and early stage companies from across the globe.

“This event is a productive opportunity to establish new connections with industry and government partners, many within easy reach of Lehigh,” said Gene Lucadamo, the industry liaison for Lehigh’s Center for Advanced Materials and Nanotechnology and the Lehigh Nanotech Network.

“Some of these connections are with alumni in business or government, and even with nearby Pennsylvania companies that were attracted to Lehigh innovations. These interactions allow us to promote research capabilities and facilities which are available through our Industry Liaison Program, and to identify opportunities for collaborations and funding.”

In addition to the three National Innovator Awards, Lehigh researchers won seven National Innovation Showcase awards and presented five conference papers in areas as diverse as the biomanufacturing of quantum dots, a 3-D imaging technique 20 times faster than current systems, the creation of a miniature medical oxygen concentrator for patients with Chronic Obstructive Pulmonary Disease (COPD), and a biomedically superior bioactive glass that mimics bone.

Attendees include innovators, funding agencies, national and federal labs, international research organizations, universities, tech transfer offices and investment and corporate partners. The 2015 TechConnect World Innovation event encompasses the 2015 SBIR/STTR National Conference, the 2015 National Innovation Summit and Showcase, and Nanotech2015—the world’s largest nanotechnology event.

The following is a list of the Lehigh faculty members who gave presentations at TechConnect 2015:

•    A wavy micropatterned microfluidic device for capturing circulating tumor cells (Principal investigator: Liu)

•    Bioengineered enzymes that safely and cheaply fight bacterial biofilms (Principal investigator: Berger)

•    New reagents for octafluorocyclobutane transfer that eliminate the use of hazardous tetrafluoroethylene (Principal investigator: Vicic)

•    A method to cheaply manufacture quantum dots using bacteria (Principal investigator: Berger)

•    A multiplexing optical coherence tomography technology 20 times faster than current systems that preserves image resolution and allows synchronized cross-sectional and three-dimensional (3D) imaging. (Principal investigator: Chao Zhou, electrical and computer engineering)

•    A miniature medical oxygen concentrator for COPD patients (Principal investigator: Mayuresh Kothare, chemical and biomolecular engineering)

•    A biomedically superior bioactive glass that enables the production of porous bone scaffolds that can be tailored to match the tissue growth rate of a given patient type (Principal investigator: Himanshu Jain, materials science and engineering)

•    A new distributed-feedback technique that dramatically improves the laser beam patterns and increases the output power levels of semiconductor lasers (Principal investigator: Sushil Kumar, electrical and computer engineering)

•    A new pretreatment process to remove unwanted impurities in ceramic powders without any change in the physical properties, leading to better reproducibility of properties and reliability in the final products (Principal investigator: Martin Harmer, materials science and engineering)

Story by Jordan Reese

Lehigh University: Biomanufacturing of CdS Quantum Dots

Lehigh QD 062415 id40545A team of Lehigh University engineers have demonstrated a bacterial method for the low-cost, environmentally friendly synthesis of aqueous soluble quantum dot (QD) nanocrystals at room temperature.
Principal researchers Steven McIntosh, Bryan Berger and Christopher Kiely, along with a team of chemical engineering, bioengineering, and material science students present this novel approach for the reproducible biosynthesis of extracellular, water-soluble QDs in the July 1 issue of the journal Green Chemistry (“Biomanufacturing of CdS quantum dots”). This is the first example of engineers harnessing nature’s unique ability to achieve cost effective and scalable manufacturing of QDs using a bacterial process.
Biomanufacturing of CdS Quantum Dots
Using an engineered strain of Stenotrophomonas maltophilia to control particle size, Lehigh researchers biosynthesized quantum dots using bacteria and cadmium sulfide to provide a route to low-cost, scalable and green synthesis of CdS nanocrystals with extrinsic crystallite size control in the quantum confinement range. The result is CdS semiconductor nanocrystals with associated size-dependent band gap and photoluminescent properties. (Image: Linda Nye for Lehigh University)
Using an engineered strain of Stenotrophomonas maltophilia to control particle size, the team biosynthesized QDs using bacteria and cadmium sulfide to provide a route to low-cost, scalable and green synthesis of CdS nanocrystals with extrinsic crystallite size control in the quantum confinement range. The solution yields extracellular, water-soluble quantum dots from low-cost precursors at ambient temperatures and pressure. The result is CdS semiconductor nanocrystals with associated size-dependent band gap and photoluminescent properties.
This biosynthetic approach provides a viable pathway to realize the promise of green biomanufacturing of these materials. The Lehigh team presented this process recently to a national showcase of investors and industrial partners at the TechConnect 2015 World Innovation Conference and National Innovation Showcase in Washington, D.C. June 14-17.
“Biosynthetic QDs will enable the development of an environmentally-friendly, bio-inspired process unlike current approaches that rely on high temperatures, pressures, toxic solvents and expensive precursors,” Berger says. “We have developed a unique, ‘green’ approach that substantially reduces both cost and environmental impact.”
Quantum dots, which have use in diverse applications such as medical imaging, lighting, display technologies, solar cells, photocatalysts, renewable energy and optoelectronics, are typically expensive and complicated to manufacture. In particular, current chemical synthesis methods use high temperatures and toxic solvents, which make environmental remediation expensive and challenging.
This newly described process allows for the manufacturing of quantum dots using an environmentally benign process and at a fraction of the cost. Whereas in conventional production techniques QDs currently cost $1,000-$10,000 per gram, the biomanufacturing technique cuts that cost to about $1-$10 per gram. The substantial reduction in cost potentially enables large-scale production of QDs viable for use in commercial applications.
“We estimate yields on the order of grams per liter from batch cultures under optimized conditions, and are able to reproduce a wide size range of CdS QDs,” said Steven McIntosh.
The research is funded by the National Science Foundation’s Division of Emerging Frontiers in Research and Innovation (EFRI Grant No. 1332349) and builds on the success of the initial funding, supplied by Lehigh’s Faculty Innovation Grant (FIG) and Collaborative Research Opportunity Grant (CORE) programs.
The Lehigh research group is also investigating, through the NSF’s EFRI division, the expansion of this work to include a wide range of other functional materials. Functional materials are those with controlled composition, size, and structure to facilitate desired interactions with light, electrical or magnetic fields, or chemical environment to provide unique functionality in a wide range of applications from energy to medicine.
McIntosh said, “While biosynthesis of structural materials is relatively well established, harnessing nature to create functional inorganic materials will provide a pathway to a future environmentally friendly biomanufacturing based economy. We believe that this work is the first step on this path.”
Source: Lehigh University