Tag Archives: Angela M. Belcher

100 percent efficiency transporting the energy of sunlight from receptors to reaction centers

Genetic engineering has been combined with elements of quantum physics to find a better way of transferring the energy derived from sunlight from the receptors to the reaction centers (i.e., photosynthesis). From an Oct. 15, 2015 news item on Nanowerk,

Nature has had billions of years to perfect photosynthesis, which directly or indirectly supports virtually all life on Earth. In that time, the process has achieved almost 100 percent efficiency in transporting the energy of sunlight from receptors to reaction centers where it can be harnessed — a performance vastly better than even the best solar cells.

One way plants achieve this efficiency is by making use of the exotic effects of quantum mechanics — effects sometimes known as “quantum weirdness.” These effects, which include the ability of a particle to exist in more than one place at a time [superposition], have now been used by engineers at MIT to achieve a significant efficiency boost in a light-harvesting system.

Surprisingly, the MIT [Massachusetts Institute of Technology] researchers achieved this new approach to solar energy not with high-tech materials or microchips — but by using genetically engineered viruses.

An Oct. 15, 2015 MIT news release (also on EurekAlert), which originated the news item, recounts an exciting tale of interdisciplinary work and an international collaboration,

This achievement in coupling quantum research and genetic manipulation, described this week in the journal Nature Materials, was the work of MIT professors Angela Belcher, an expert on engineering viruses to carry out energy-related tasks, and Seth Lloyd, an expert on quantum theory and its potential applications; research associate Heechul Park; and 14 collaborators at MIT and in Italy.

Lloyd, a professor of mechanical engineering, explains that in photosynthesis, a photon hits a receptor called a chromophore, which in turn produces an exciton — a quantum particle of energy. This exciton jumps from one chromophore to another until it reaches a reaction center, where that energy is harnessed to build the molecules that support life.

But the hopping pathway is random and inefficient unless it takes advantage of quantum effects that allow it, in effect, to take multiple pathways at once and select the best ones, behaving more like a wave than a particle.

This efficient movement of excitons has one key requirement: The chromophores have to be arranged just right, with exactly the right amount of space between them. This, Lloyd explains, is known as the “Quantum Goldilocks Effect.”

That’s where the virus comes in. By engineering a virus that Belcher has worked with for years, the team was able to get it to bond with multiple synthetic chromophores — or, in this case, organic dyes. The researchers were then able to produce many varieties of the virus, with slightly different spacings between those synthetic chromophores, and select the ones that performed best.

In the end, they were able to more than double excitons’ speed, increasing the distance they traveled before dissipating — a significant improvement in the efficiency of the process.

The project started from a chance meeting at a conference in Italy. Lloyd and Belcher, a professor of biological engineering, were reporting on different projects they had worked on, and began discussing the possibility of a project encompassing their very different expertise. Lloyd, whose work is mostly theoretical, pointed out that the viruses Belcher works with have the right length scales to potentially support quantum effects.

In 2008, Lloyd had published a paper demonstrating that photosynthetic organisms transmit light energy efficiently because of these quantum effects. When he saw Belcher’s report on her work with engineered viruses, he wondered if that might provide a way to artificially induce a similar effect, in an effort to approach nature’s efficiency.

“I had been talking about potential systems you could use to demonstrate this effect, and Angela said, ‘We’re already making those,'” Lloyd recalls. Eventually, after much analysis, “We came up with design principles to redesign how the virus is capturing light, and get it to this quantum regime.”

Within two weeks, Belcher’s team had created their first test version of the engineered virus. Many months of work then went into perfecting the receptors and the spacings.

Once the team engineered the viruses, they were able to use laser spectroscopy and dynamical modeling to watch the light-harvesting process in action, and to demonstrate that the new viruses were indeed making use of quantum coherence to enhance the transport of excitons.

“It was really fun,” Belcher says. “A group of us who spoke different [scientific] languages worked closely together, to both make this class of organisms, and analyze the data. That’s why I’m so excited by this.”

While this initial result is essentially a proof of concept rather than a practical system, it points the way toward an approach that could lead to inexpensive and efficient solar cells or light-driven catalysis, the team says. So far, the engineered viruses collect and transport energy from incoming light, but do not yet harness it to produce power (as in solar cells) or molecules (as in photosynthesis). But this could be done by adding a reaction center, where such processing takes place, to the end of the virus where the excitons end up.

MIT has produced a video explanation of the work,

Here’s a link to and a citation for the paper,

Enhanced energy transport in genetically engineered excitonic networks by Heechul Park, Nimrod Heldman, Patrick Rebentrost, Luigi Abbondanza, Alessandro Iagatti, Andrea Alessi, Barbara Patrizi, Mario Salvalaggio, Laura Bussotti, Masoud Mohseni, Filippo Caruso, Hannah C. Johnsen, Roberto Fusco, Paolo Foggi, Petra F. Scudo, Seth Lloyd, & Angela M. Belcher. Nature Materials (2015) doi:10.1038/nmat4448 Published online 12 October 2015

This paper is behind a paywall.

A millionth of a trillionth of a gram: attoscale weight

Researchers at the Massachusetts Institute of Technology (MIT) have found a means of measuring particle weight, with increased accuracy, at the attoscale according to a Jan. 13, 2014 news item on ScienceDaily,

MIT engineers have devised a way to measure the mass of particles with a resolution better than an attogram — one millionth of a trillionth of a gram. Weighing these tiny particles, including both synthetic nanoparticles and biological components of cells, could help researchers better understand their composition and function.

The Jan. 13, 2014 MIT news release by Anne Trafton (also on EurekAlert), which originated the news item, describes the origins of the technology that the researchers adapted to achieve increased resolution,

The system builds on a technology previously developed by Scott Manalis, an MIT professor of biological and mechanical engineering, to weigh larger particles, such as cells. This system, known as a suspended microchannel resonator (SMR), measures the particles’ mass as they flow through a narrow channel.

By shrinking the size of the entire system, the researchers were able to boost its resolution to 0.85 attograms —more than a 30-fold improvement over the previous generation of the device.

“Now we can weigh small viruses, extracellular vesicles, and most of the engineered nanoparticles that are being used for nanomedicine,” says Selim Olcum, a postdoc in Manalis’ lab  …

Manalis first developed the SMR system in 2007 to measure the mass of living cells, as well as particles as small as a femtogram (one quadrillionth of a gram, or 1,000 attograms). Since then, his lab has used the device to track cell growth over time, measure cell density, and measure other physical properties, such as stiffness.

The original mass sensor consists of a fluid-filled microchannel etched in a tiny silicon cantilever that vibrates inside a vacuum cavity. As cells or particles flow through the channel, one at a time, their mass slightly alters the cantilever’s vibration frequency. The mass of the particle can be calculated from that change in frequency.

To make the device sensitive to smaller masses, the researchers had to shrink the size of the cantilever, which behaves much like a diving board, Olcum says. When a diver bounces at the end of a diving board, it vibrates with a very large amplitude and low frequency. When the diver plunges into the water, the board begins to vibrate much faster because the total mass of the board has dropped considerably.

To measure smaller masses, a smaller “diving board” is required. “If you’re measuring nanoparticles with a large cantilever, it’s like having a huge diving board with a tiny fly on it. When the fly jumps off, you don’t notice any difference. That’s why we had to make very tiny diving boards,” Olcum says.

In a previous study, researchers in Manalis’ lab built a 50-micron cantilever — about one-tenth the size of the cantilever used for measuring cells. That system, known as a suspended nanochannel resonator (SNR), was able to weigh particles as light as 77 attograms at a rate of a particle or two per second.

Here’s how the scientists accomplished their latest goal of getting more precise measurements of weight (from the news release),

The cantilever in the new version of the SNR device is 22.5 microns long, and the channel that runs across it is 1 micron wide and 400 nanometers deep. This miniaturization makes the system more sensitive because it increases the cantilever’s vibration frequency. At higher frequencies, the cantilever is more responsive to smaller changes in mass.

The researchers got another boost in resolution by switching the source for the cantilever’s vibration from an electrostatic to a piezoelectric excitation, which produces a larger amplitude and, in turn, decreases the impact of spurious vibrations that interfere with the signal they are trying to measure.

With this system, the researchers can measure nearly 30,000 particles in a little more than 90 minutes. “In the span of a second, we’ve got four or five particles going through, and we could potentially increase the concentration and have particles going through faster,” Cermak says.

To demonstrate the device’s usefulness in analyzing engineered nanoparticles, the MIT team weighed nanoparticles made of DNA bound to tiny gold spheres, which allowed them to determine how many gold spheres were bound to each DNA-origami scaffold. That information can be used to assess yield, which is important for developing precise nanostructures, such as scaffolds for nanodevices.

The researchers also tested the SNR system on biological nanoparticles called exosomes — vesicles that carry proteins, RNA, or other molecules secreted by cells — which are believed to play a role in signaling between distant locations in the body.

They found that exosomes secreted by liver cells and fibroblasts (cells that make up connective tissue) had different profiles of mass distribution, suggesting that it may be possible to distinguish vesicles that originate from different cells and may have different biological functions.

The researchers are now investigating using the SNR device to detect exosomes in the blood of patients with glioblastoma (GBM), a type of brain cancer. This type of tumor secretes large quantities of exosomes, and tracking changes in their concentration could help doctors monitor patients as they are treated.

Glioblastoma exosomes can now be detected by mixing blood samples with magnetic nanoparticles coated with antibodies that bind to markers found on vesicle surfaces, but the SNR could provide a simpler test.

Here’s a link to and a citation for the researchers’ abstract,

Weighing nanoparticles in solution at the attogram scale by Selim Olcuma, Nathan Cermak, Steven C. Wasserman, Kathleen S. Christine, Hiroshi Atsumi, Kris R. Payer, Wenjiang Shen, Jungchul Lee, Angela M. Belcher, Sangeeta N. Bhatia, and Scott R. Manalis. Proceedings of the National Academy of Sciences of the United States of America (PNAS), doi: 10.1073/pnas.1318602111 Published online Jan. 13, 2014

This article is behind a paywall.

Biology and lithium-air batteries

Firstly, the biology in question is that of viruses and, secondly, research in lithium-air batteries has elicited big interest according to David Chandler’s November 13, 2013 Massachusetts Institute of Technology (MIT) news piece (also on EurekAlert and Nanowerk),

Lithium-air batteries have become a hot research area in recent years: They hold the promise of drastically increasing power per battery weight, which could lead, for example, to electric cars with a much greater driving range. But bringing that promise to reality has faced a number of challenges, ….

Now, MIT researchers have found that adding genetically modified viruses to the production of nanowires — wires that are about the width of a red blood cell, and which can serve as one of a battery’s electrodes — could help solve some of these problems.

Lithium-air batteries can also be referred to as lithiium-oxygen batteries, although Chandler does not choose to mix terms as he goes on to describe the process the researchers developed,

The researchers produced an array of nanowires, each about 80 nanometers across, using a genetically modified virus called M13, which can capture molecules of metals from water and bind them into structural shapes. In this case, wires of manganese oxide — a “favorite material” for a lithium-air battery’s cathode, Belcher says — were actually made by the viruses. But unlike wires “grown” through conventional chemical methods, these virus-built nanowires have a rough, spiky surface, which dramatically increases their surface area.

Belcher, the W.M. Keck Professor of Energy and a member of MIT’s Koch Institute for Integrative Cancer Research, explains that this process of biosynthesis is “really similar to how an abalone grows its shell” — in that case, by collecting calcium from seawater and depositing it into a solid, linked structure.

The increase in surface area produced by this method can provide “a big advantage,” Belcher says, in lithium-air batteries’ rate of charging and discharging. But the process also has other potential advantages, she says: Unlike conventional fabrication methods, which involve energy-intensive high temperatures and hazardous chemicals, this process can be carried out at room temperature using a water-based process.

Also, rather than isolated wires, the viruses naturally produce a three-dimensional structure of cross-linked wires, which provides greater stability for an electrode.

A final part of the process is the addition of a small amount of a metal, such as palladium, which greatly increases the electrical conductivity of the nanowires and allows them to catalyze reactions that take place during charging and discharging. Other groups have tried to produce such batteries using pure or highly concentrated metals as the electrodes, but this new process drastically lowers how much of the expensive material is needed.

Altogether, these modifications have the potential to produce a battery that could provide two to three times greater energy density — the amount of energy that can be stored for a given weight — than today’s best lithium-ion batteries, a closely related technology that is today’s top contender, the researchers say.

MIT has produced a video highlighting the researchers’ work (this runs longer than most of the materials I embed here at approximately 11 mins. 25 secs.),

For those who want to know more about this intriguing and speculative work,

Biologically enhanced cathode design for improved capacity and cycle life for lithium-oxygen batteries by Dahyun Oh, Jifa Qi, Yi-Chun Lu, Yong Zhang, Yang Shao-Horn, & Angela M. Belcher. Nature Communications 4, Article number: 2756 doi:10.1038/ncomms3756 Published 13 November 2013

This article is behind a paywall.

ETA Nov. 15, 2013: Dexter Johnson offers more context and information, including commercialization issues, about lithium-air batteries and lithium-ion batteries in his Nov. 14, 2013 posting on the Nanoclast blog (on the IEEE [Institute of Electrical and Electronics Engineers] website).