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European cities could suffer under climate change

Climate change could push European cities to breaking point, warns a new study in Environmental Research Letters (ERL). In the largest undertaking of its kind, a team from Newcastle University, UK, looked at all 571 cities in Europe.

Their models showed unprecedented increases in drought, heatwaves and flooding, with some areas set to face intensification of more than one hazard. The team made continent-wide comparisons possible for the first time by applying a consistent method.

Under the highest impact scenario, no city is immune from stronger and more frequent heatwaves by the end of the century, the researchers found. Although southern Europe may see more heatwaves per year, central European cities will be affected by the most dramatic temperature increases – of up to 14°C. For the first time, the team also brought to light possible worsening of drought in northern cities.

The increased risk of flooding to the British Isles was one of the report’s most striking findings. Even under the most optimistic scenario, 85% of UK cities are projected to face more flooding. Cities including Cork, Carlisle and Wrexham could see more than a 50% increase in peak river flow. In the worst-case scenario, only 9 cities in the study are immune to a greater flood risk.

Previously, projections of river flooding changes for Europe have been inconsistent. By using a longer analysis interval of 50 years, and one-in-ten year, rather than one-in-100 year, floods, Selma Guerreiro and colleagues teased out a strong north-south divide.

The team used results from climate model runs forced with a high greenhouse gas emissions trajectory known as Representative Concentration Pathway (RCP) 8.5, which assumes a forcing of 8.5 W/m² by the year 2100. Under this scenario, the emissions curve begins to flatten only after mid-century.

“We used RCP 8.5 because we wanted to assess the impact of climate change in European cities if severe emission reductions do not happen,” said Guerreiro. “The work started in 2013, when there was no international agreement in place. However, it is still relevant since the national commitments from the Paris agreement imply a global temperature increase of around 3 degrees, well within the temperature range covered by RCP8.5.”

The response of the Earth system to climate forcing is still uncertain. To explore the full range of possible outcomes, the team used the whole ensemble of climate projections from the fifth Coupled Model Intercomparison Project (CMIP5), presenting the data in low (10%), medium (50%) and high (90%) impact categories. These represent the percentiles for each hazard for each city, indicating the range of outcomes rather than probability.

The team was particularly concerned about the findings for dramatic increases in drought in southern Europe. They describe a picture of “a fundamentally different climate” for the region, a scenario that present infrastructure may not be prepared for.

Now the group is combining its work on hazards with research into vulnerability. This will build up a complete picture of risk under unmitigated climate change, helping decision makers prioritise investments for adaptation.

Planar nanostructure provides giant chirality

Intrinsic chirality is typically a property of 3D objects that lack a plane of mirror symmetry. A team of researchers in the USA and Singapore have manipulated the electric, magnetic and toroidal moments in a 2D dielectric chiral nanostructure to generate a large chiroptical response at optical frequencies, illuminated under normal incidence, with an easily fabricated design.

Manipulating the polarization of light is fundamental to many emerging areas of physics. It allows the creation of holograms, helps in producing ultra-compact, flat lenses and paves the way to digital and programmable metasurfaces. In this pursuit, chiral structures are crucial, but before now no efficient and easily fabricated devices have been produced for optical frequencies.

Chiral structures lack mirror symmetry and are found across all length scales in biology and chemistry. Chirality is typically detected through a differential response to left- and right-handed circularly polarized light (LCP and RCP). This is measured as either circular dichroism (a difference in transmission intensities) or circular birefringence (a rotation of the plane of linearly polarized light). Generally termed chiroptical responses, these tend to be very small in naturally occurring chiral materials. Recent work on manufacturing artificial chiral structures, such as arrays of 3D helices or 2D gammadions, has led to some improvement. However, 3D structures are difficult to manufacture for optical frequencies, and 2D materials only work at oblique incidence due to fundamental symmetry considerations, and are considered extrinsic chiral objects.

However, researchers at Harvard University and the National University of Singapore have reconsidered this problem, and found a neat solution by inducing high-order multipole resonances in a 2D chiral structure that replicate the symmetry of a 3D chiral structure.

Interacting electric and magnetic moments

A chiroptical response originates from the interaction of electric and magnetic moments. In 2D structures, electric currents are constrained to be tangential and lie in the plane of the structure, so magnetic moments (which are orthogonal to the electric ones) are always out of the plane. Therefore typically the way to achieve overlap between the electric and magnetic moments is to illuminate these 2D structures at an oblique angle, thereby realizing an extrinsic chiral response.

In contrast, 3D chiral structures, such as helices, support electric currents out of the plane of the array. These give rise to in-plane magnetic moments that can interact strongly with the electric moments, producing strong intrinsic chiroptical activity under illumination at normal incidence.

The key to the structure proposed and studied in this recent work is that it is made of a dielectric with a high refractive index; titanium oxide. In high-index dielectric structures of a thickness comparable to the wavelength, out-of-plane electric displacement currents exist. These displacement currents mean that electric and magnetic moments can overlap, even at normal incidence in a planar structure.

Chiroptical activity from high-order multipoles

The researchers created a 2D array of planar gammadions using electron beam lithography and atomic layer deposition of TiO₂. The notion that a 2D planar structure with a plane of mirror symmetry can exhibit a large chiroptical response at normal incidence is counter-intuitive. However, the out-of-plane displacement currents and associated magnetic moments provide the necessary broken symmetry. The circular dichroism measured experimentally was around 80%, with a circular birefringence of 100,000 degrees per unit length at 540 nm wavelength. These results far exceed the chiroptical responses of any natural materials and go beyond other state-of-the-art artificial chiral structures.

When 87% of RCP light is transmitted in the zeroth diffraction order, almost all LCP light is transmitted in the first diffraction order at ±460. A waveguide layer is included in the structure to increase the transmission in the zeroth diffracted order, but it does not contribute to the chiroptical response.

The large chiroptical response is attributed to higher-order multipoles excited in the gammadions, thanks to careful tuning of the geometry. This is in contrast to most systems, whose predominant electromagnetic response is a dipolar one. A dipole dominated system intuitively radiates at normal incidence, and thus cannot support the diffracted modes under LCP illumination. A quadrupole or higher dominated system primarily radiates off-axis, so it can accommodate this behaviour. In a chiral structure the light couples to these multipoles differently depending on the helicity, thereby giving rise to a difference in the RCP and LCP transmitted intensities.

For more information, read the full article at Light: Science & Applications.

Artificial intelligence: is there anything to fear?

Artificial intelligence (AI) bots are going to replace our jobs.

AI cars are not to be trusted, they will drive us off a cliff

AI machines will inevitably conspire to kill us all.

These are exaggerated versions of three fears commonly associated artificial intelligence (AI). Even the late Stephen Hawking spoke about a potential future in which humans could be superseded by advanced forms of artificial intelligence. But these concerns are not so present in the mind of Nathan Myhrvold, the former chief technology officer at Microsoft who once worked in Hawking’s theoretical physics group at the University of Cambridge.

AI representation — Some fear that AI robots will supersede humans (Courtesy: iStock/chombosan)

Myhrvold is the co-founder of Intellectual Ventures, which develops and licenses intellectual property. Having also written a several tomes about modernist cooking techniques, Myhrvold does not shy away from lofty academic pursuits. Earlier this year, the Seattle-born polymath presented the annual Tacitus Lecture in London with a talk entitled “Cyber-Trade: Will AI Displace or Enhance our Work?”

In our latest podcast, Andrew Glester reports from the event where he spoke to Myhrvold, who explained why he is optimistic that AI can be a force for good in the world. You will also hear clips from that lecture, a few words on the topic from Hawking himself, and a fruity anecdote from Prue Leith one of the judges from the popular TV show The Great British Bakeoff. All will be revealed!

Tale of the atom tamers

“Imagine putting the Sun in a bottle…that’s what we’re trying to do.” As an opening line in a film it’s a powerful one. Nuclear fusion is often sold as a panacea, and while it would indeed be a clean and seemingly endless source of energy, achieving and sustaining fusion in lab conditions is no mean feat. Written and directed by film-maker Mila Aung-Thwin, Let There Be Light: the 100 Year Journey to Fusion tells the story of our ongoing quest for fusion here on Earth, with a prominent focus on the science and the scientists behind ITER – the International Thermonuclear Experimental Reactor – based in France, as well as a few other fusion companies too. ITER was first proposed in 1985, as the first inkling of such technology was shared during the Cold War, when the Soviet Union’s Mikhail Gorbachev and US president Ronald Reagan agreed to collaborate “in obtaining this source of energy, which is essentially inexhaustible, for the benefit for all mankind”. Today, ITER encompasses not only the US and Russia but China, the European Union, India, Japan and Korea too.

Before going further into the film, I must point out a pet peeve of mine in documentaries, which is not knowing who is speaking for vast chunks of the film. As a viewer I dislike hearing a disembodied voice with no knowledge of who it is (as this often means a loss of context), and this was the case for the first 10 minutes or so of Let There Be Light. Apart from that small misgiving, I enjoyed the mix of artistic visuals, footage from ITER, on-screen graphics and schematics, and animated historical scenes. One of the first actual faces we meet in the film is Michel Laberge, founder and chief inventor of the private Canadian company General Fusion. He explains nuclear fission and fusion, succinctly wrapping up the whole fusion story by saying “The aim of the game is to get more energy out than you put in.”

The film also does a good job of explaining the basics of the science involved, from tokamak technology, to the toroidal magnets needed to hold the 150 million kelvin plasma, to how a gyrotron (the part that heats up the plasma) functions. This scene was particularly charming as ITER physicist Mark Henderson attempts to explain how the device works, using an analogy of creating resonance by blowing across the top of a Coke bottle. To better illustrate this fact, he sends a colleague off to buy a bottle only for the colleague to return with a (useless) can. “Man… you call yourself a physicist!” Henderson exclaims.

**Fusion vision** ITER’s Mark Henderson at the tokamak pit. (Courtesy: Van Royko)

Ken Blackler, who oversees assembly and operations at the experiment, says that “ITER is going to be built from a million pieces so it’s a real nightmare to know where pieces are.” He goes on to explain that a tokamak is built bottom up and so it is crucial that each piece is available at the right time – this involves a considerable planning effort with all of ITER’s member states, who provide different bits. Indeed, one of the big challenges that ITER faces is its complex organizational politics. Others are its ability to receive continued funding (the project in its entirety will likely cost tens of billions of euros) and the need to stay on schedule. Indeed, ITER was supposed to achieve its “first plasma” in 2016; that date has been pushed multiple times and is now likely to be 2025, as it struggles to make sure that fusion doesn’t become one of the most “expensive failures in scientific history”.

Just as I was beginning to bemoan the lack of a single woman on screen, Sabina Griffith – ITER’s communications manager – pops up, lamenting the public’s lack of awareness when it comes to ITER. She rightly points out that taxpayers around the globe allow this project to move forward, and so ITER maintains a very “transparent” communications strategy. It’s interesting to watch Griffith coach Henderson on what to say, and not to say, when it comes to funding (or the lack thereof) from its members, especially the US. She advises that instead of complaining in official reports about how funding has decreased since the 1970s, they should instead say that “it is difficult” and remind people that to achieve fusion by the middle of this century, continued funding is key. Griffith points out that if ITER does not succeed, then “fusion will be dead, forever or at least for a very very long…nobody will bet on fusion for a long time”.

Magnet challenges for ITER

Towards the end of the film, we join Henderson as he visits the tokamak pit for the first time, and chats to some of the construction workers on site, asking if they know what they are building. “The molecules and what they do is not really our department…our job is making the structure,” says one of workmen. After a quick explanation, Henderson tells them this has been his dream since he was 14 and they are helping to make it a reality. As they say their goodbyes and thank-yous, one of the workmen adds that “My dream would be that all countries in the world can benefit…that’s my dream.”

I must admit that despite writing about physics for the last seven years, I’ve never been completely clear on ITER and what goes into making fusion energy a reality. While it’s not the most slick or engaging science documentary I’ve watched, Let There Be Light goes a long way to shedding light on this epic scientific endeavour. Laberge complains that there still isn’t enough excitement about fusion, and that people don’t mention fusion when talking about alternate energy sources – “windmills, tide, solar, chicken shit, whatever… but never fusion” he grumbles. But not before adding that he will “work on this all my life until this works”.

Available worldwide for rent or purchase on the Vimeo platform, in English and French

2017 EyeSteelFilm, dir. Mila Aung-Thwin

Evidence mounts for liquid-liquid transition in supercooled water

More evidence that supercooled water exists in two distinct liquid phases has surfaced in experiments done by Austen Angell and colleagues at Arizona State University (ASU) and the University of Amsterdam. The idea of two liquid phases was proposed 25 years ago to explain the thermodynamic properties of supercooled water, but physicists had been unable to cool water to low enough temperatures to observe a transition between the phases.

The physics of water is a rich and active field of research because the substance has many poorly-understood physical properties that do not fit the mould of a normal liquid. “Water is a rather unique liquid,” says Angell. For instance, liquid water exhibits negative thermal expansion below 4 °C, meaning that its volume expands as it cools instead of contracting like most liquids.

One hotly-debated issue for scientists studying water is the “second critical point hypothesis”. This suggests that at low temperatures liquid water makes a transition from its familiar liquid phase to a lower density phase that is also more viscous.

Adding antifreeze

Angel and colleagues study supercooled water by adding the antifreeze hydrazinium trifluoracetate to pure water to create a water-like liquid that can be chilled to temperatures below -90 °C without freezing. This was necessary because pure water can only be supercooled to around -40 °C and the team believed that the transition occurred well below this temperature.

A few years ago, Angell and his ASU colleague Zuofeng Zhao noticed that when the solution was cooled to about -80 °C it suddenly gave off heat – something that is consistent with a phase transition. The new liquid was much more viscous than water and Angell and Zhao could reverse the transition by increasing the temperature. What they could not do at the time was to confirm that the water molecules in the new phase are arranged differently than in conventional liquid water.

Now, the ASU researchers have teamed up with Sander Woutersen and colleagues in Amsterdam to probe the structure of the new phase using infrared spectroscopy. They found that the lower density liquid phase has stronger and more ordered hydrogen bonds around the water molecules, which make the liquid stiffer and therefore more viscous. Further analysis revealed that the hydrogen bonding patterns involved in the transition between the two liquid phases are analogous to those observed in a different transition between two glassy states of pure water ice.

Purity issues

While this lends credence to the idea that results from the study expose the hidden liquid phase of pure water, the fact that the liquid is not pure water was always likely to lead some to question whether the antifreeze could have some influence on the results.

“The work is certainly very interesting,” says Alan Soper of the UK’s Rutherford Appleton Laboratory. “But liquid–liquid transitions are often observed in mixed systems, so how this relates to the properties of pure water I am not clear.” Soper also questions the use of infrared measurements to infer what is happening at the molecular level, when there might be other explanations for the data.

Yet evidence is mounting that a liquid–liquid transition may indeed occur in supercooled water. Earlier this year researchers in Sweden, Japan and Korea used ultrafast X-ray scattering to measure the properties of -44 °C supercooled water droplets and concluded that supercooled water could exist in two different liquid phases with different densities.

Angell and colleagues describe their latest work in Science.

Biopen speeds up stem-cell repair

Printing results from the biopen — The biopen in action

As 3D printing technology evolves and advances, we are getting ever closer to the goal of being able to implant 3D printed tissues inside the body. At present, 3D printed cells must first be cultivated and then allowed to grow into viable tissue – which normally takes a few days. But a new instrument, dubbed the biopen, could help to speed up this process. The biopen, developed by researchers in Australia, could allow surgeons to repair damaged bone and cartilage by “drawing” new cells directly onto bone during surgery and then filling in any damaged areas.

The researchers, led by Gordon Wallace of the University of Wollongong in close collaboration with Peter Choong, an orthopaedic surgeon at St Vincent’s Hospital in Melbourne, first reported their technique in the journal Biofabrication in 2016, and have now tested it out in experiments with sheep.

“The data obtained to date is highly promising,” says Wallace. “We are continuing to optimize printing protocols to demonstrate the versatility of the biopen.” The team is also now working with a manufacturer to produce a commercial device.

The prototype pen described in Biofabrication is made of medical grade ABS-like material and titanium 6Al4V alloy. It works by extruding a bioink, composed of stem cells inside a biopolymer, onto the surface of bone or cartilage. The ink is then solidified by photocuring it with light from an ultraviolet source fitted to the side of the pen. The device draws the stem-cell-containing structures directly onto a defect, and these structures subsequently differentiate into cartilage.

Specific clinical applications

In their paper, Wallace and colleagues report on using biopolymers such as those based on alginate, a seaweed extract, which was in turn protected by a hydrogel. Since then, they have been trying to identify other naturally occurring sources of biopolymers that may be suitable for bioinks, subject to some chemical modification.

“The biopen was our first foray into customized printing approaches for specific clinical applications,” Wallace told Physics World. “We now have an advanced programme for developing specially-designed printers and bioink formulations for use in a number of areas.”

“One of these is treating eye damage in the iFixpen project, which is a collaborative venture with the Sydney Eye Hospital,” Wallace continues. “Another is fabricating 3D-printed structures containing human islet cells for transplantation, which we are working on in association with the Royal Adelaide Hospital.”

A third project – which aims to create 3D printed ears for children with part of an ear missing – has also brought some interesting challenges, he adds. In this case multimaterial and stem-cell-containing structures must be printed in the appropriate shape, which has required the researchers to develop multiple ink formulations and a multihead printing system that will be provided by the Royal Price Alfred Hospital in Sydney.

“We also have a new fundamental research programme looking at printing and developing stem cells, such as induced pluripotent stem cells, and how they develop into neurons,” reveals Wallace. “This work will help us to obtain new insights into neural diseases.”

This article is one of a series of reports reviewing progress on high-impact research originally published in the IOP Publishing journal Biofabrication.

Stephen Hawking’s last paper predicts a smooth exit from eternal inflation

What was Stephen Hawking working on just before his death last week?

While I’m sure he had several irons in the fire, he had just put the finishing touches on a paper about inflation and the multiverse – which he co-authored with Thomas Hertog of the University of Leuven in Belgian.

“A smooth exit from eternal inflation?” was uploaded to the arXiv preprint server in July 2017 and was updated on 4 March, just 10 days before Hawking’s death. According to reports in several media outlets, the paper has been submitted to a journal for peer review.

The paper presents preliminary calculations that combine quantum and classical physics. The research explores whether an “infinite fractal-like multiverse” was created by the cosmic inflation that occurred just after the Big Bang. Hawking and Hertog’s calculations seem to say no.

Collagen sponge heals tendon

Researchers in Beijing have engineered the protein SDF-1α (stromal cell-derived factor-1α) to tether to collagen, enabling controlled release of SDF-1α to promote cell migration towards the site of injury in tendon (Biomaterials 162 22).

Tendon injury is common, and not only in athletes. Unfortunately, current treatments do not provide satisfying results due to a high tearing recurrence. To address this matter, many studies are investigating how to associate cells to a scaffold to promote regeneration. However, the administration of exogenous cells can lead to ethical issues and also raises the question of which cell source is the most suitable.

Another strategy is to attract endogenous cells to the scaffold using chemo-attractant molecules. SDF-1α induces the migration of different cell types, including mesenchymal stem cells, dermal fibroblasts and Achilles tendon fibroblasts. A limitation in the use of SDF-1α – despite the fact that it has been shown to trigger regeneration of several organs, including tendon – is that it diffuses too fast in vivo, which reduces its local concentration and thus its efficacy.

Jianwu Dai and his team at the Chinese Academy of Sciences have engineered SDF-1α by adding a protein fragment that can bind to collagen (collagen binding domain, CBD) to control its release. The authors chose collagen type I as the scaffold due to its good biocompatibility and mechanical properties. Also, type I collagen is the main component of the extracellular matrix (ECM), which is the scaffold that cells secrete to support themselves.

The researchers attached this CBD-SDF-1α to a type I collagen sponge and studied its behaviour in vitro and in vivo (in a rat Achilles tendon defect model). SDF-1α acts on cells through a receptor named CXCR4 localized on the cell surface. Tracking cells that express this marker provides a way to determine whether SDF-1α triggers their migration.

CBD-SDF-1α attachment and release
The authors first checked that the addition of the CBD to SDF-1α didn’t alter its bioactivity, and that it can attach to the collagen scaffold. They found that release of CBD-SDF-1α from the scaffold was slow. After nine days, 61% of the molecules were released, with more time required for complete release. This report showing a slow release profile of the molecule-of-interest is one of the few in the field.

Later, the researchers observed in vivo that CBD-SDF-1α scaffold triggers the recruitment of more CXCR4-positive cells than the controls of collagen sponges without SDF-1α and with native SDF-1α (not modified). These cells deposit ECM and tenascin C, a marker of the healing tendon. They also saw no excessive amount of cells from the immune system migrating to the injury area, suggesting that CBD-SDF-1α didn’t induce immune cell reaction.

CBD-SDF-1α scaffold triggers cell migration

Formation of new tendon
The scaffold gave place to the formation of new tendon tissue after one week, although more time is required for it to resemble to a native tendon. The mechanical properties of the neo-tendon (the force that the tendon can withstand and the stiffness) were superior to those of the control systems. These superior properties are explained by the fact that, in vivo, tendon is made of collagen fibrils, which are highly organized and aligned. In this study, collagen fibrils in the CBD-SDF-1α group were larger and aligned, and the cells aligned with them.

One limitation of most investigations is the formation of bone instead of tendon at the site of injury, mainly due to the differentiation of stem cells to bone cells. In contrast, in this work, CBD-SDF-1α scaffold didn’t promote bone formation.

This study is highly encouraging for the development of collagen sponges tailored with specific features for tissue engineering. In future work, this CBD-SDF-1α sponge should be studied in larger animal models and for other applications, such as healing bone, cartilage and many more.

Ocean acidification weakens coral skeletons

Coral reefs are under a barrage of threats. Ocean acidification alone could decrease the density of coral skeletons by up to 20%, with reefs close to the equator affected most.

Declines in coral skeletal density could have wide-reaching impacts on reef structure. Reefs are a natural coastal defence, shielding coastlines from storms by dissipating much of their energy. But “less dense skeletons will provide a weaker barrier,” said Nathan Mollica of Massachusetts Institute of Technology, US.

Such a decline could also render reefs more vulnerable to erosion. “There is some evidence that a lower density skeleton may be more easily bored into by bio-eroding organisms,” said Mollica, suggesting there may be wider implications for reef health.

The study, published in PNAS, showed that reefs in the coral triangle – a diversity hotspot in the western Pacific – are likely to be most at risk. Large increases in seawater acidity are predicted for this region. In areas that experience only small changes in acidity, coral skeletons could well stay strong.

Ocean acidification reduces the availability of the carbonate ions that corals need to grow. However, studies of coral growth in acidified environments in the lab and field have yielded mixed results, making it hard to predict how corals will respond to future change. The answer, it seems, lies in understanding the different ways that these organisms grow.

Corals develop in two ways: by extending outwards at the edges, and by thickening bundles of existing crystals to make the coral skeleton denser. This thickening is vulnerable to ocean acidification.

Scientists believe that corals have more control over their outwards growth than the thickening of their central skeleton. As these areas are under less control, they may be more susceptible to changes in seawater chemistry.

By separating the two key components of coral growth, the team simulated how coral skeletons will change by the end of the century, validating their model with reef data from around the world.

Many studies have seen a relationship between seawater chemistry and skeletal growth. “Our model builds on that by allowing us not only to predict how corals will respond to [acidification], but put a number on it which is really valuable when making long term predictions,” said Mollica.

Currently, the model works best for Porites, a stony coral that dominates tropical reefs around the world. With some calibration it could apply to other taxa, allowing researchers to unpack the impact of ocean acidification on other corals.

“The future for coral reefs is certainly scary but all is not lost,” said Anne Cohen of Woods Hole Oceanographic Institute, US. “We have to continue to work hard to stabilize and even reduce carbon dioxide in the atmosphere and in the meantime take very good care of our reefs to optimize their ability to deal with the coming changes.”

Genetic manipulation unlocks key to nature’s palette

Researchers have used genetic modifications to directly control structural colour appearing in nature. The work is an important step towards understanding how nature has evolved to effortlessly grow and control functional nanostructures, in the hope that we can harness these tools. The knowledge can be applied to create novel, biodegradable optical materials and sensors with myriad possibilities: for example, photonic materials designed so they are self-healing and can easily interface with living tissues. The findings by a collaboration of researchers from the University of Cambridge and Hoekmine BV are published in PNAS.

When a Hoekmine BV team unexpectedly discovered that they had isolated a previously unknown, brilliantly green coloured strain of bacteria, they contacted researchers at University of Cambridge to investigate this phenomenon further. According to Villads Egede Johansen, co-first author of this work, “from that point onwards, we were both driven to explore what can be done to alter and influence this system”.

The ensuing experimental work represents the first systematic study linking genetic markers to structural colour, with the hope that more studies will now be sparked in this direction. Striking examples of structural colour, which refers to colour that is not obtained through pigmentation, are found in natural phenomena such as butterfly wings and peacock feathers. Genetic control of macroscopic properties such as colour opens the door to an almost limitless number of material and device fabrication options.

From bacteria to sensors

The bacteria used as a model system in this research is the Flavobacterium IR1 strain. These are rod-shaped bacteria that are able to pack together through gliding and growing mechanisms. Under different genetic and environmental conditions, Flavobacterium colonies form ordered nanostructures that interfere with light to give distinctive bright green, yellow, blue and red iridescent colorations, spanning the entire visible spectrum.

The iridescent colours are highly distinctive, meaning they have great potential for use as cheap and effective chemical sensors. For example, the bacteria could be genetically engineered to lose colour upon exposure to a specific chemical compound. This builds on existing concepts such as using sensors to “sniff out” drug production in sewers and using bacteria to detect explosives such as landmines. Other applications being considered are biodegradable paints and colorants, giving rise to the idea that we could even grow our own customized paints from different bacterial colonies.

Microscopic Petri palette of dried up genetically altered bacteria colonies.

A brightly irridescent future

To drive this research forwards, it is imperative to further understand the biological functions of the packing that leads to this distinctive expression of colour. The researchers were the first to link these packing mechanisms to both optical response, or manifestation of colour, and to certain genetic markers.

However, the eternal ‘nature versus nurture’ issue must also be considered, as it was observed that not only do genetic markers influence how the colonies exhibit colour, environmental changes have a distinctive effect. Fucoidan is a sulphated polymer derived from brown algae that the scientists found enhances the structural coloration. This discovery highlights the need for further research in this field to fully understand genetically modified colour.

Using genetics to alter and influence the material response of biological systems paves the way forward to a bright and shimmering future, filled with biodegradable, eco-friendly nanofunctional materials grown to fulfil our planet’s ever-increasing demands on resources.

Full details of the research are reported in Proceedings of the National Academy of Sciences 10.1073/pnas.1716214115.

Browse articles by content type

European cities could suffer under climate change

Planar nanostructure provides giant chirality

Interacting electric and magnetic moments

Chiroptical activity from high-order multipoles

Artificial intelligence: is there anything to fear?