How synthetic viruses can boost green energy production

The Biomimicry Column

How synthetic viruses can boost green energy production

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Viruses are a fascination in our world: On the one hand, they are reputed to be the most common living thing in the world, but on the other, they not considered living at all, as they are not able to reproduce themselves and lack a cell structure. Clearly they are a critical part of a little understood web of life that encompasses horizontal gene transfer, random selection and the ebb and flow of population growth and decline.

They are, especially, survivors, but they need a host in order to pass on their DNA. One key to their success, therefore, is the ability to selectively bind to this host. A science team at the Massachusetts Institute of Technology (MIT) is studying this capability to improve the performance of green energy technologies.

Angela Belcher leads the team and is an all-star of bio-inspired design. She is the W.M. Keck Professor of Energy at MIT and a faculty member at the David H. Koch Institute for Integrative Cancer Research. She has just received this year's Lemelson-MIT Prize, which honors an outstanding inventor dedicated to improving the world through technological invention.

Inspired by nature in her youth, Belcher turned a fascination with the biomineralization of the abalone shell into her Ph.D dissertation at the University of California, Santa Barbara. She is now one of the world's foremost experts in nanotechnology and heads the Biomolecular Materials Group at MIT. Her group studies how to combine organic and inorganic materials together, much as the abalone manufactures a complex matrix of proteins and minerals for strength. The team focuses on getting biological materials to work with inorganic materials, such as metals and semi-conductors.

Belcher is continually asking two questions: How can we impart genetic information coding for materials? Can we get living organisms to work with more of the periodic table?

She and her talented students work in the zone where biomaterials and nanotechnology meet, and their inspiration is DNA as it is used as a precise toolkit among nature's "biomineralizers," such as the abalone or diatoms or magnetotatic bacteria.

Much of their work is with engineered viruses. Belcher invented a process in which she genetically engineers the DNA of bacteriophages (benign bacterial specific viruses) to interact with inorganic materials. By splicing new genes into the DNA sequence of a phage her researchers are able to create new phages. This is repeated in rapid random selection with billions of viruses until a huge peptide library has been assembled. The most promising combinations of genes present a molecular arrangement with an affinity for a material of interest, such as a metal or semi-conductor. These are then tested for use.

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Two significant breakthroughs

This process recently has yielded two notable inventions: a lithium-ion battery and a solar cell treatment that uses phages to assemble nanotubes to collect energy. The battery is inexpensive to produce and nontoxic, while the nanotube technology collects energy 33 percent more efficiently than typical dye-sensitized panels.

Traditional lithium-ion batteries use graphite as the anode or negative post and cobalt oxide or lithium iron phosphate as the cathode or positive post of the battery. In the new technology, bacteriophages are used as templates to grow nanowires of, say, cobalt oxide. Metals, such as gold, are bonded to these nanowires and then a macro self-assembly of them initiated. The viruses' ability to recognize and bind to specific inorganic substances allows carbon nanowires to be connected to the carbon nanotube network, thus boosting the electrical conductance of the device. Belcher calls the moment when her students correlated this binding ability to power output one of the highpoints of her career.

This approach is notably bio-inspired in several ways. First, it uses an accelerated random selection process to evolve solutions. These DNA sequence codes for assembly are applied not to proteins, however, but to inorganic materials. Second, it uses self-assembly and selective binding to create structures. This "bio-molecular recognition" allowed the electrochemically active nanowires to be hooked up to the energy-boosting nanotube network. Third, it does so without caustic solvents or toxic building materials or extreme heat, unlike typical manufacturing. Fourth, because it is built from the bottom up from small modules, it is conforming and diversifiable. In other words, it can be integrated into other forms and processes.

The MIT group claims power performance comparable to more traditional lithium-ion batteries, and is working on improving the device's ability to hold a charge. Many combinations of organic and inorganic materials have been tried since the initial successes. They are currently experimenting with bio-templating manganese oxide nanowires and coating them with various metal nanoparticles to increase surface area for more power and cyclability.

For the solar panel improvement the team used the same synthetic virus, M13, as a template for assembling single-walled carbon nanotubes with a titanium dioxide nanocrystal core-shell composite. These nanotubes exhibit "high electron mobility" and collect photo-generated electrons very efficiently. They had been, however, difficult to incorporate into nanocomposites. The group was able to demonstrate that using nanocomposites as photoanodes within the dye-sensitized solar cell could achieve a power conversion efficiency of 10.6 percent.

In a dye-sensitized solar cell, light excites the dye much as it does the thylakoids in a living plant. Excited electrons flow from the dye through to a transparent conductor. Belcher wondered what their virus-based process could do to improve power output. A high dye load and a direct path to the conductor were desired, so the challenge was to provide efficient carbon nanotube pathways to the conductor that didn't limit the density of the dye. High surface area also was desired, but carbon nanotubes are hydrophobic so tend to clump together. The team tested various versions of the M13 virus for binding in order to separate the carbon nanotubes and prevent this clumping and used it as a surfactant in the liquid mixture in order to coat the nanowires with metals such as titanium or semi-conducting materials.

Solar panel image by Fedorov Oleksiy via Shutterstock.

Applying biomimicry in the marketplace

Belcher has co-founded two companies: Cambrios Technologies and Siluria Technologies. Cambrios develops electronic materials for transparent coatings used for touch screens, LCDs and other devices, while Siluria converts lower-value methane gas into high-value liquid transportation fuel and other products.

At Siluria, researchers are producing so-called bio-fuels, but the intent is to use biological components as templates only for a final product that is strictly inorganic. The company uses more available and cheaper methane and converts it to higher grade ethylene for fuel and chemicals. It has just completed a series C round of funding and is striving to commercialize the process.

Traditionally, methane gas has been converted by oxidative coupling (OCM), but 30 years of research has yet to yield a commercially viable process. Siluria's mission is to convert this methane to ethylene using biological catalysts and low temperatures to break the famously tenacious chemical bonds of the methane. The process for this is similar to the others described: make a biotemplate, synthesize nanowire catalysts, screen the catalysts for best fit in the OCM reaction, and then optimize catalyst performance.

Again, the selectivity of the catalyst binding is key to the advantage of this approach. Success would mean a cheaper, cleaner and more versatile alternative to oil.

Solar panel image by Fedorov Oleksiy via Shutterstock.