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ILP Institute Insider

May 2, 2013

Finding the Molecular Needle in the Haystack

Isolating individual molecules to detect explosives, treat diabetes, manufacture graphene, and capture light.

Steve Calechman

To hear Michael S. Strano explain his work, it sounds simple. “I’m interested in the chemical engineering of what are called low dimensional materials,” he says.

Michael S. Strano
Charles and Hilda Roddey
Professor of Chemical Engineering
In practice, the Charles and Hilda Roddey Professor of Chemical Engineering focuses on using quantum-confining nanotechnology, be it graphene, single-walled carbon nanotubes or nanowires, to impart new properties to familiar materials and systems, and then to apply them to a wide variety of engineering problems. It could be glucose monitoring for diabetes management; explosive and environmental toxin detection; rooftop coatings; or light harvesting and solar energy conversion. Whatever the area, Strano’s hope is to develop technologies that are both more efficient and productive while also being more affordable and accessible.

Picking out a single molecule
In essence, much of Strano’s work involves using nanotechnology to create recognition sites that have the ability to not only identify a single, isolated molecule but also trace elements from countless components. “It’s the needle in the haystack problem,” Strano says. One notable area is in explosive detection, and, for the potential solution, he received an assist from nature with a series of peptides found in bee venom that can recognize different nitroaromatic molecules. In his lab, he created a sensor by coating single-walled carbon nanotubes with the peptides, or bombolitins. When a target binds with the venom proteins, it shifts the fluorescent light’s wavelength, giving a more accurate reading than measuring the light’s intensity, he says.

The approach offers flexibility since different proteins can be used on different nanotubes, and, with that, the ability to detect single molecules, within a complex mixture, at room temperature and atmospheric pressure. Basically, it’s a fingerprint for not just each compound, but also for the components of the compound. “We think it’s going to transform the analytical chemistry of molecular detection,” Strano says.



While the device could mean more sensitive airport security screening, Strano says that the technology can also be used for pesticides, gas leaks and environmental toxins. The further benefit is that the nanosensors are low-power and low-cost and could be networked through smartphones to cover a wide area of locations and people could share and correlate information with each other in real-time. “I see this as potentially empowering technology,” he says.

Mitigating the effects of diabetes
Strano’s focus is chemical engineering, but his work crosses over into medicine. “We pioneered and designed a unique glucose recognition site,” he says. The device, a kind of sensitive tattoo, uses a special kind of nanoparticle that can be placed anywhere in the body and will fluoresce in the near infrared in response to the amount of glucose in the blood. This system eliminates the need for daily finger prick tests, and, instead, provides a passive, long-term, real-time way for people with diabetes to monitor their levels, Strano says.

While the tattoo is less invasive, Strano sees more significant benefits to the nanotechnology. “It has the potential to be part of the solution of completely mitigating the disease of diabetes,” he says. Certain negative consequences, such as heart disease, blindness and amputation, happen over time because of the constant, sharp spikes in glucose and insulin. Daily finger prick tests can’t detect every fluctuation, but the infrared light not only can make such readings but also it can make immediate interventions with the needed adjustments, Strano says. The tattoo is in the animal testing phase, and it will be a while before it can be tried with people, but Strano says that he’s hopeful. “The concept is there,” he says.

Furthering the possibilities, MIT technology may form the basis of an artificial pancreas, which would hook up the sensor to an insulin pump, forming a closed loop of monitoring and response. The missing piece is a long-term sensor that works inside the body, but, as Strano says, “We have all the technology available to complete that loop.”

Creating graphene for wide-spread use
One of the continual challenges in nanotechnology is being able to use and manufacture graphene on a large-scale. Strano’s work could lead to that. He’s created a bi-layer graphene, two stacked layers with a band gap in between. An electronic field could be applied and the electronic structure could then be distorted, opening up the material to sensors and digital electronics, he says.

Along with the stacking, Strano has developed a graphene ink. By chemically spreading apart the graphene layers, a solution of graphene and organic solvent can be created. Used as a coating, it wouldn’t change the properties of a surface but would create a new class of materials that would be corrosion-resistant and would block molecules from passing through. The single layer could be spread out over a wide area and be used on or in rooftops, vehicles, water purification systems or gas separation. Along with graphene being stronger than what’s found in nature, the building blocks for it are earth-abundant and less expansive. “You can make them by burning trash,” he says.

Capturing more light
One other area that Strano is exploring is using nanotechnology to harvest near infrared light and converting it to electrical energy. As it stands, 40 percent of energy in the solar spectrum is in this range—light so red that the eye can’t see it—but it’s not captured and therefore wasted, he says. Strano’s created a device that combines a conventional silicon-based photovoltaic cell with an all-carbon cell. As light comes into the device, each of the active layers will harvest an increasing portion of the spectrum while also controlling the temperature of the conventional cells, which tend to heat up and lose efficiency during the process.

Along with this, Strano has developed antennae out of single-walled carbon nanotubes. Looking like a carbon fiber, the device acts as a funnel for photons, concentrating and collecting them toward the center and allowing more light to be obtained than with merely a flat panel. Taken all together, Strano says that the devices would be new tools in light harvesting, harnessing more for less and ultimately increasing the efficiency of solar energy conversion. “We need new materials and methods for harvesting and concentrating solar energy,” he says. “Nanotechnology has a significant role to play in this space.”