Quantum physics meets genetic engineering

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, have now been used by engineers at MIT to achieve a significant efficiency boost in a light-harvesting system.

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

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.

“This is exciting and high-quality research,” says Alán Aspuru-Guzik, a professor of chemistry and chemical biology at Harvard University who was not involved in this work. The research, he says, “combines the work of a leader in theory (Lloyd) and a leader in experiment (Belcher) in a truly multidisciplinary and exciting combination that spans biology to physics to potentially, future technology.”

“​Access to controllable excitonic systems is a goal shared by many researchers in the field,” Aspuru-Guzik adds. “This work provides fundamental understanding that can allow for the development of devices with an increased control of exciton flow.”

The research was supported by the Italian energy company Eni through the MIT Energy Initiative. In addition to MIT postdocs Nimrod Heldman and Patrick Rebentrost, the team included researchers at the University of Florence, the University of Perugia, and Eni.

MIT

Quantum biology - algae evolved to switch quantum coherence on and off

Scanning electron microscope image of cryptophytes. Image: CSIRO

A UNSW-led team of researchers has discovered how algae that survive in very low levels of light are able to switch on and off a weird quantum phenomenon that occurs during photosynthesis.

The function in the algae of this quantum effect, known as coherence, remains a mystery, but it is thought it could help them harvest energy from the sun much more efficiently.

Working out its role in a living organism could lead to technological advances, such as better organic solar cells and quantum-based electronic devices.

The research is published in the journal Proceedings of the National Academy of Sciences.

It is part of an emerging field called quantum biology, in which evidence is growing that quantum phenomena are operating in nature, not just the laboratory, and may even account for how birds can navigate using the earth’s magnetic field.

“We studied tiny single-celled algae called cryptophytes that thrive in the bottom of pools of water, or under thick ice, where very little light reaches them,” says senior author, Professor Paul Curmi, of the UNSW School of Physics.

“Most cryptophytes have a light-harvesting system where quantum coherence is present. But we have found a class of cryptophytes where it is switched off because of a genetic mutation that alters the shape of a light-harvesting protein.

“This is a very exciting find. It means we will be able to uncover the role of quantum coherence in photosynthesis by comparing organisms with the two different types of proteins.”

In the weird world of quantum physics, a system that is coherent – with all quantum waves in step with each other – can exist in many different states simultaneously, an effect known as superposition. This phenomenon is usually only observed under tightly controlled laboratory conditions.

So the team, which includes Professor Gregory Scholes from the University of Toronto in Canada, was surprised to discover in 2010 that the transfer of energy between molecules in the light harvesting systems from two different cryptophyte species was coherent.

The same effect has been found in green sulphur bacteria that also survive in very low light levels.

“The assumption is that this could increase the efficiency of photosynthesis, allowing the algae and bacteria to exist on almost no light,” says Professor Curmi.

“Once a light-harvesting protein has captured sunlight, it needs to get that trapped energy to the reaction centre in the cell as quickly as possible, where the energy is converted into chemical energy for the organism.

“It was assumed the energy gets to the reaction centre in a random fashion, like a drunk staggering home. But quantum coherence would allow the energy to test every possible pathway simultaneously before travelling via the quickest route.”

In the new study, the team used x-ray crystallography to work out the crystal structure of the light-harvesting complexes from three different species of cryptophytes.

They found that in two species a genetic mutation has led to the insertion of an extra amino acid that changes the structure of the protein complex, disrupting coherence.

“This shows cryptophytes have evolved an elegant but powerful genetic switch to control coherence and change the mechanisms used for light harvesting,” says Professor Curmi.

The next step will be to compare the biology of different cryptophytes, such as whether they inhabit different environmental niches, to work out whether the quantum coherence effect is assisting their survival.

The team was led by UNSW’s Dr Stephen Harrop and Dr Krystyna Wilk, and includes researchers from the University of Toronto, the University of Padua, the University of British Columbia, the University of Cologne and Macquarie University.

Quantum biology: Do weird physics effects abound in nature?

Disappearing in one place and reappearing in another. Being in two places at once. Communicating information seemingly faster than the speed of light.

This kind of weird behaviour is commonplace in dark, still laboratories studying the branch of physics called quantum mechanics, but what might it have to do with fresh flowers, migrating birds, and the smell of rotten eggs?

Welcome to the frontier of what is called quantum biology.

It is still a tentative, even speculative discipline, but what scientists are learning from it might just spark revolutions in the development of new drugs, computers and perfumes - or even help in the fight against cancer.

Until recently, the delicate states of matter predicted by quantum mechanics have only been accessed with the most careful experiments: isolated particles at blisteringly low temperatures or pressures approaching that of deep space.

The idea that biology - impossibly warm, wet and messy to your average physicist - should play host to these states was almost heretical.

But a few strands of evidence were bringing the idea into the mainstream, said Luca Turin of the Fleming Institute in Greece.

"There are definitely three areas that have turned out to be manifestly quantum," Dr Turin told the BBC. "These three things... have dispelled the idea that quantum mechanics had nothing to say about biology."

The most established of the three is photosynthesis - the staggeringly efficient process by which plants and some bacteria build the molecules they need, using energy from sunlight. It seems to use what is called "superposition" - being seemingly in more than one place at one time.

Watch the process closely enough and it appears there are little packets of energy simultaneously "trying" all of the possible paths to get where they need to go, and then settling on the most efficient.

"Biology seems to have been able to use these subtle effects in a warm, wet environment and still maintain the [superposition]. How it does that we don't understand," Richard Cogdell of the University of Glasgow told the BBC.

But the surprise may not stop at plants - there are good hints that the trickery is present in animals, too: the navigational feats of birds that cross countries, continents or even fly pole to pole present a compelling behavioural case.

Experiments show that European robins only oriented themselves for migration under certain colours of light, and that very weak radio waves could completely mix up their sense of direction. Neither should affect the standard compass that biologists once believed birds had within their cells.

What makes more sense is the quantum effect of entanglement. Under quantum rules, no matter how far apart an "entangled" pair of particles gets, each seems to "know" what the other is up to - they can even seem to pass information to one another faster than the speed of light.

The weird world of quantum mechanics

Quantum mechanics starts with the simple idea that energy does not come in just any amount; it comes in discrete chunks, called quanta. But deeper into the theory, some truly surprising - and useful - effects crop up.

Superposition: A particle exists in a number of possible states or locations simultaneously - strictly, an electron might be in the tip of your finger and in the furthest corner of the Universe at the same time. It is only when we observe the particle that it 'chooses' one particular state.

Entanglement: Two particles can become entangled so that their properties depend on each other - no matter how far apart they get. A measurement of one seems to affect the measurement of the other instantaneously - an idea even Einstein called "spooky".

Tunnelling: A particle can break through an energy barrier, seeming to disappear on one side of it and reappear on the other. Lots of modern electronics and imaging depends on this effect.

Experiments suggest this is going on within single molecules in birds' eyes, and John Morton of University College London explained that the way birds sense it could be stranger still.

"You could think about that as... a kind of 'heads-up display' like what pilots have: an image of the magnetic field... imprinted on top of the image that they see around them," he said.

The idea continues to be somewhat controversial - as is the one that your nose might be doing a bit of quantum biology.

Most smell researchers think the way that we smell has to do only with the shapes of odour molecules matching those of receptors in our noses.

But Dr Turin believes that the way smell molecules wiggle and vibrate is responsible - thanks to the quantum effect called tunnelling.

The idea holds that electrons in the receptors in our noses disappear on one side of a smell molecule and reappear on the other, leaving a little bit of energy behind in the process.

A paper published in Plos One shows that people can tell the difference between two molecules of identical shape but with different vibrations, suggesting that shape is not the only thing at work.

What intrigues all these researchers is how much more quantum trickery may be out there in nature.

"Are these three fields the tip of the iceberg, or is there actually no iceberg underneath?" asked Dr Turin. "We just don't know. And we won't know until we go and look."

'Hugely important'

That question has ignited a global push. In 2012, the European Science Foundation launched its Farquest programme, aiming to map out a pan-European quantum research structure in which quantum biology plays a big role.

And the US defence research agency, Darpa, has been running a nationwide quantum biology network since 2010. Departments dedicated to the topic are springing up in countries ranging from Germany to India.

A better understanding of smell could make the hit-and-miss business of making new fragrances more directed, and learning from nature's tricks could help with developing next-generation quantum computers.

But what the next wave of quantum biologists finds could be truly profound.

Simon Gane, a researcher at the Royal National Throat, Nose and Ear Hospital and lead author of the Plos One paper, said that the tiny receptors in our noses are what are called G-protein coupled receptors.

"They're a sub-family of the receptors we have on all cells in our body - they're the targets of most drug development," he explained.

"What if - and this is a very big if - there's a major form of receptor-drug interaction that we're just not noticing because we're not looking for a quantum effect? That would have profound implications for drug development, design and discovery."

Jim Al-Khalili of the University of Surrey is investigating whether tunnelling occurs during mutations to our DNA - a question that may be relevant to the evolution of life itself, or cancer research.

He told the BBC: "If quantum tunnelling is an important mechanism in mutations, is quantum mechanics going to somehow answer some of the questions about how a cell becomes cancerous?

"And suddenly you think, 'Wow!' Quantum mechanics is not just a crazy side issue or a fringe field where some people are looking at some cranky ideas. If it really might help answer some of the very big questions in science, then it's hugely important."

Source: http://www.bbc.com/news/science-environment-21150047