Microscopy and optical imaging are important tools in basic research and biomedicine. They use substances that can release light when excited. Known as “fluorophores,” these substances are used to stain very small structures in samples, enabling clear resolution using modern microscopes. Most fluorophores shine in the range of light visible to humans. When using light in the near infrared spectrum, with a wavelength starting at 800 nanometres, light penetrates even deeper into tissue and there are fewer distortions to the image. So far, however, there are only a few known fluorophores that work in the near infrared spectrum.

The research team has now succeeded in exfoliating extremely thin layers from grains of calcium copper silicate, also known as Egyptian blue. These nanosheets are 100,000 times thinner than a human hair and fluoresce in the near infrared range. “We were able to show that even the smallest nanosheets are extremely stable, shine brightly and do not bleach,” says Dr Sebastian Kruss, “making them ideal for optical imaging.”

The scientists tested their idea for microscopy in animals and plants. For example, they followed the movement of individual nanosheets in order to visualise mechanical processes and the structure of the tissue around cell nuclei in the fruit fly. In addition, they integrated the nanosheets into plants and were able to identify them even without a microscope, which promises future applications in the agricultural industry. “The potential for state-of-the-art microscopy from this material means that new findings in biomedical research can be expected in the future,” says Kruss.

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The study suggests that people may acquire the coronavirus through the air and after touching contaminated objects. Scientists discovered the virus is detectable for up to three hours in aerosols, up to four hours on copper, up to 24 hours on cardboard and up to two to three days on plastic and stainless steel.

“This virus is quite transmissible through relatively casual contact, making this pathogen very hard to contain,” said James Lloyd-Smith, a co-author of the study and a UCLA professor of ecology and evolutionary biology. “If you’re touching items that someone else has recently handled, be aware they could be contaminated and wash your hands.”

The study attempted to mimic the virus being deposited onto everyday surfaces in a household or hospital setting by an infected person through coughing or touching objects, for example. The scientists then investigated how long the virus remained infectious on these surfaces.

The study’s authors are from UCLA, the National Institutes of Health’s National Institute of Allergy and Infectious Diseases, the Centers for Disease Control and Prevention, and Princeton University. They include Amandine Gamble, a UCLA postdoctoral researcher in Lloyd-Smith’s laboratory.

In February, Lloyd-Smith and colleagues reported in the journal eLife that screening travelers for COVID-19 is not very effective. People infected with the virus — officially named SARS-CoV-2 — may be spreading the virus without knowing they have it or before symptoms appear. Lloyd-Smith said the biology and epidemiology of the virus make infection extremely difficult to detect in its early stages because the majority of cases show no symptoms for five days or longer after exposure.

“Many people won’t have developed symptoms yet,” Lloyd-Smith said. “Based on our earlier analysis of flu pandemic data, many people may not choose to disclose if they do know.”

The new study supports guidance from public health professionals to slow the spread of COVID-19:

• Avoid close contact with people who are sick.
• Avoid touching your eyes, nose and mouth.
• Stay home when you are sick.
• Cover coughs or sneezes with a tissue, and dispose of the tissue in the trash.
• Clean and disinfect frequently touched objects and surfaces using a household cleaning spray or wipe.

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Materials provided by University of California – Los Angeles. Note: Content may be edited for style and length.

The universe has been expanding since the Big Bang occurred 13.8 billion years ago — a proposition first made by the Belgian canon and physicist Georges Lemaître (1894-1966), and first demonstrated by Edwin Hubble (1889-1953). The American astronomer discovered in 1929 that every galaxy is pulling away from us, and that the most distant galaxies are moving the most quickly. This suggests that there was a time in the past when all the galaxies were located at the same spot, a time that can only correspond to the Big Bang. This research gave rise to the Hubble-Lemaître law, including the Hubble constant (H0), which denotes the universe’s rate of expansion. The best H0 estimates currently lie around 70 (km/s)/Mpc (meaning that the universe is expanding 70 kilometres a second more quickly every 3.26 million light years). The problem is that there are two conflicting methods of calculation.

Sporadic supernovae

The first is based on the cosmic microwave background: this is the microwave radiation that comes at us from everywhere, emitted at the time the universe became cold enough for light finally to be able to circulate freely (about 370,000 years after the Big Bang). Using the precise data supplied by the Planck space mission, and given the fact that the universe is homogeneous and isotropic, a value of 67.4 is obtained for H0 using Einstein’s theory of general relativity to run through the scenario. The second calculation method is based on the supernovae which appear sporadically in distant galaxies. These very bright events provide the observer with highly precise distances, an approach that has made it possible to determine a value for H0 of 74.

Lucas Lombriser, a professor in the Theoretical Physics Department in UNIGE’s Faculty of Sciences, explains: “These two values carried on becoming more precise for many years while remaining different from each other. It didn’t take much to spark a scientific controversy and even to arouse the exciting hope that we were perhaps dealing with a ‘new physics’.” To narrow the gap, professor Lombriser entertained the idea that the universe is not as homogeneous as claimed, a hypothesis that may seem obvious on relatively modest scales. There is no doubt that matter is distributed differently inside a galaxy than outside one. It is more difficult, however, to imagine fluctuations in the average density of matter calculated on volumes thousands of times larger than a galaxy.

The “Hubble Bubble”

“If we were in a kind of gigantic ‘bubble’, continues professor Lombriser, where the density of matter was significantly lower than the known density for the entire universe, it would have consequences on the distances of supernovae and, ultimately, on determining H0.”

All that would be needed would be for this “Hubble bubble” to be large enough to include the galaxy that serves as a reference for measuring distances. By establishing a diameter of 250 million light years for this bubble, the physicist calculated that if the density of matter inside was 50% lower than for the rest of the universe, a new value would be obtained for the Hubble constant, which would then agree with the one obtained using the cosmic microwave background. “The probability that there is such a fluctuation on this scale is 1 in 20 to 1 in 5, says professor Lombriser, which means that it is not a theoretician’s fantasy. There are a lot of regions like ours in the vast universe.”

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“Nobody has taken these 2D silicon electronics and matched them to the three-dimensional architecture of the brain before,” said Abdulmalik Obaid, a graduate student in materials science and engineering at Stanford. “We had to throw out what we already know about conventional chip fabrication and design new processes to bring silicon electronics into the third dimension. And we had to do it in a way that could scale up easily.”

The device, the subject of a paper published March 20 in Science Advances, contains a bundle of microwires, with each wire less than half the width of the thinnest human hair. These thin wires can be gently inserted into the brain and connected on the outside directly to a silicon chip that records the electrical brain signals passing by each wire — like making a movie of neural electrical activity. Current versions of the device include hundreds of microwires but future versions could contain thousands.

“Electrical activity is one of the highest-resolution ways of looking at brain activity,” said Nick Melosh, professor of materials science and engineering at Stanford and co-senior author of the paper. “With this microwire array, we can see what’s happening on the single-neuron level.”

The researchers tested their brain-machine interface on isolated retinal cells from rats and in the brains of living mice. In both cases, they successfully obtained meaningful signals across the array’s hundreds of channels. Ongoing research will further determine how long the device can remain in the brain and what these signals can reveal. The team is especially interested in what the signals can tell them about learning. The researchers are also working on applications in prosthetics, particularly speech assistance.

Worth the wait

The researchers knew that, in order to achieve their aims, they had to create a brain-machine interface that was not only long-lasting, but also capable of establishing a close connection with the brain while causing minimal damage. They focused on connecting to silicon-based devices in order to take advantage of advances in those technologies.

“Silicon chips are so powerful and have an incredible ability to scale up,” said Melosh. “Our array couples with that technology very simply. You can actually just take the chip, press it onto the exposed end of the bundle and get the signals.”

One main challenge the researchers tackled was figuring out how to structure the array. It had to be strong and durable, even though its main components are hundreds of minuscule wires. The solution was to wrap each wire in a biologically-safe polymer and then bundle them together inside a metal collar. This assures the wires are spaced apart and properly oriented. Below the collar, the polymer is removed so that the wires can be individually directed into the brain.

Existing brain-machine interface devices are limited to about 100 wires offering 100 channels of signal, and each must be painstakingly placed in the array by hand. The researchers spent years refining their design and fabrication techniques to enable the creation of an array with thousands of channels — their efforts supported, in part, by a Wu Tsai Neurosciences Institute Big Ideas grant.

“The design of this device is completely different from any existing high-density recording devices, and the shape, size and density of the array can be simply varied during fabrication. This means that we can simultaneously record different brain regions at different depths with virtually any 3D arrangement,” said Jun Ding, assistant professor of neurosurgery and neurology, and co-author of the paper. “If applied broadly, this technology will greatly excel our understanding of brain function in health and disease states.”

After spending years pursuing this ambitious-yet-elegant idea, it was not until the very end of the process that they had a device that could be tested in living tissue.

“We had to take kilometers of microwires and produce large-scale arrays, then directly connect them to silicon chips,” said Obaid, who is lead author of the paper. “After years of working on that design, we tested it on the retina for the first time and it worked right away. It was extremely reassuring.”

Following their initial tests on the retina and in mice, the researchers are now conducting longer-term animal studies to check the durability of the array and the performance of large-scale versions. They are also exploring what kind of data their device can report. Results so far indicate they may be able to watch learning and failure as they are happening in the brain. The researchers are optimistic about being able to someday use the array to improve medical technologies for humans, such as mechanical prosthetics and devices that help restore speech and vision.

This research was supported by the National Institutes of Health, DARPA, the Wu Tsai Neurosciences Institute, the Francis Crick Institute, the Wellcome Trust, the Human Frontier Science Program, and the Medical Research Council.

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Materials provided by Stanford University. Original written by Taylor Kubota. Note: Content may be edited for style and length.

The photoelectric effect, whereby photons impinging on matter cause the emission of electrons, is one of the quintessential effects of quantum mechanics. Einstein famously explained the key mechanism underlying the phenomenon in 1905, earning him the 1921 Nobel Prize in Physics. He built on a concept introduced merely five years earlier by Max Planck: electromagnetic energy is absorbed and emitted only in discrete packets — that is, in quanta. The quantum concept revolutionised physics. The photoelectric effect, for its part, has been explored in ever greater detail, and is nowadays exploited in applications ranging from solar cells to night-vision goggles. A shift in our understanding of the effect came in the past decade or so. Laser experiments made it possible to look directly at the intricate quantum dynamics that unfold at the attosecond timescale as electrons are removed from their parent system when they interact with light. However, time-resolved measurements of the photoionization process in its arguably purest form — the absorption and emission of single photons by a single unbound electron — remained elusive. Until now.

Writing in the journal Optica, Jaco Fuchs and colleagues in the Ultrafast Laser Physics group of Prof. Ursula Keller at the Institute of Quantum Electronics, working with collaborators in the US, Austria and Spain, report an experiment in which they measured for the first time how the absorption and emission of single photons alters the dynamics of an electron that is not bound to an atomic nucleus, but still feels its Coulomb potential. Introducing a novel experimental protocol, they found that the dynamics depends on the angular momentum of the photoionized electron: they measured a delay of up to 12 attoseconds between outgoing s- and d-electrons in helium. This is a subtle yet unmistakable signature of underlying quantum-mechanical effects. And they observed fundamental phenomena of classical origin, too: they measured phase changes that reflect that in d-electrons the outward propagation is slower than in s-electrons. This can be explained by the larger fraction of rotational energy and hence a lower radial energy in d-electrons.

Extracting the contribution of single photons

These results mark several ‘firsts’. The Keller group has pioneered various areas of attoscience, including the measurement of attosecond time delays in photoionsation, which arise as photoexcited electrons propagate in the potential of the parent ion, resulting in a measurable group delay. The measurement of these attosecond-scale time delays typically involves at least two photons, making it exceptionally difficult to extract the contribution of single photons. Fuchs et al. now found a way to do just that.

In their case two photons are involved too, one in the extreme ultraviolet (XUV) and the other in the infrared (IR) range. But they devised a fitting procedure that enabled them to extract from their high-quality data the amplitudes and relative phases of all the quantum pathways through which photoionsation proceeds in their system. In this way they were able to isolate the different contributions of the IR photons, which are the ones inducing transitions in an unbound electron (whereas the XUV photons ionise the atom, by transferring an electron from a bound state to the continuum).

Direct measurement of delays arising from Bremsstrahlung

Not only did the ETH physicists gain for the first time access to time delays from any one-photon transition. Theirs are also the first measurements of such time delays for the absorption and emission of photons by unbound electrons, a phenomenon known as (inverse) Bremsstrahlung. The experimental results are well reproduced by two independent theoretical methods Fuchs and colleagues employed. These simulations also provide evidence that some of the observed effects are universal, in the sense that they are independent of the atomic species of the parent ion.

This work illustrates that also 115 years after Einstein’s seminal work, the photoelectric effect does not cease to inspire. The tools introduced by Fuchs and co-workers provide new experimental capabilities for studying photoionization dynamics, both in atoms and in small molecules. Such studies could in turn provide a fuller understanding of photoemission time delays, in particular in the presence of interactions in the intermediate-to-long range.

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Using a fish species from the Baltic Sea, the three-spined stickleback, an international team investigated whether and how epigenetics contributes to adaptation. “Our experiment shows that epigenetic modifications affect adaptation, but also that the changes from one generation to the next are smaller than previously assumed,” says biologist Dr. Melanie Heckwolf from GEOMAR Helmholtz Centre for Ocean Research Kiel. She is one author of the study, which has now been published in Science Advances.

But what distinguishes changes in DNA from changes in epigenetics? “Individuals with certain heritable traits encoded in the DNA can cope with the prevailing environment better than others. On average, those individuals can cope better with their environment, hence survive longer and produce more offspring. In the long run, their characteristics encoded in the DNA will prevail. This process refers to natural selection,” explains Dr. Britta Meyer from GEOMAR. However, selection requires time, and time is scarce in the face of rapid climate change.

In contrast, epigenetic processes chemically influence the structure of the DNA. They activate or deactivate areas of the genome that are responsible for certain traits or responses to environmental conditions. On the one hand, “stable” epigenetic markers, through natural selection, contribute to adaptation in a similar way as the DNA itself. On the other hand, “inducible” markers are those that can change during the life of an individual. In theory, if this happens in the gametes of the parents, their offspring are given an advantage to cope with their environment. Many scientists therefore expect that inducible markers will react particularly quickly and thus ensure the survival of organisms in the face of rapid changes.

The research groups of Prof. Dr. Thorsten Reusch (GEOMAR, Germany) and Dr. Christophe Eizaguirre (Queen Mary University of London, UK) have investigated whether and how these stable and inducible markers contribute to adaptation. They use the Baltic three-spined stickleback fish because it is currently adapted to different salinity conditions ranging from saltwater to freshwater. Further, the Baltic Sea is a natural laboratory for climate change research because the effects of climate change are already evident there.

“In order to understand how fish respond to the consequences of climate change, we collected stickleback populations from different regions of the North and Baltic Seas with different salinity levels,” explains Dr. Meyer. The team found that the different populations differed in their genetic and epigenetic makeups and also had different tolerances to changes in salinity. In an experiment involving two generations of sticklebacks, the team was also able to show that inducible markers improve the response of the second generation to environmental change, albeit to a lesser extent than initially assumed.

Overall, the study shows that organisms will eventually reach their limits to respond to climate change, even with epigenetic modes of adaptation. “We have to be careful not to overinterpret this exciting but poorly understood field of research in epigenetics as a silver bullet against climate change for all species,” says Melanie Heckwolf. “Climate change is one of the greatest challenges for species and ecosystems, and the natural mechanisms available to species to respond may not be sufficient if climate change remains so strong and rapid.”

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Now, researchers at MIT have come up with a way of getting conductive polymer gels to adhere to wet surfaces.

The new adhesive method is described in the journal Science Advances in a paper by MIT doctoral student Hyunwoo Yuk, former visiting scholar Akihisa Inoue, postdoc Baoyang Lu, and professor of mechanical engineering Xuanhe Zhao.

Most electrodes used for biomedical devices are made of platinum or platinum-iridium alloys, Zhao explains. These are very good electrical conductors that are durable inside the moist environment of the body, and chemically stable so they do not interact with the surrounding tissues. But their stiffness is a major drawback. Because they can’t flex and stretch as the body moves, they can damage delicate tissues.

Conductive polymers such as PEDOT:PSS, by contrast, can very closely match the softness and flexibility of the vulnerable tissues in the body. The tricky part has been getting them to stay attached to the biomedical devices they are connected to. Researchers have been struggling for years to make these polymers durable in the moist and always-moving environments of the body.

“There have been thousands of papers talking about the advantages of these materials,” Yuk says, but the companies that make biomedical devices “just don’t use them,” because they need materials that are exceedingly reliable and stable. A failure of the material could require an invasive surgical procedure to replace it, which carries additional risk for the patient.

Stiff metal electrodes “sometimes harm the tissues, but they work well in terms of reliability and stability over a period of years,” which has not been the case with polymer substitutes until now, he says.

Most efforts to address this problem have involved making significant modifications to the polymer materials to improve their durability and their ability to adhere, but Yuk says that creates problems of its own: Companies have already invested heavily in equipment to manufacture these polymers, and major changes to the formulation would require significant investment in new production equipment. These changes would be for a market that is relatively small in economic terms, though large in potential impact. Other approaches that have been tried are limited to specific materials. Instead, the MIT team focused on making the fewest changes possible, to ensure compatibility with existing production methods, and making the method applicable to a wide variety of materials.

Their method involves an extremely thin adhesive layer between the conductive polymer hydrogel and the substrate material. Though only a few nanometers thick (billionths of a meter), this layer turns out to be effective at making the gels adhere to any of a wide variety of commonly used substrate materials, including glass, polyimide, indium tin oxide, and gold. The adhesive layer penetrates into the polymer itself, producing a tough, durable protective structure that keeps the material in place even when exposed for long periods to a wet environment.

The adhesive layer can be applied to the devices by a variety of standard manufacturing processes, including spin coating, spray coating, and dip coating, making it easy to integrate with existing fabrication platforms. The coating the researchers used in their tests is made of polyurethane, a hydrophilic (water-attracting) material that is readily available and inexpensive, though other similar polymers could also be used. Such materials “become very strong when they form interpenetrating networks,” as they do when coated on the conducting polymer, Yuk explains. This enhanced strength should address the durability problems associated with the uncoated polymer, he says.

The result is a mechanically strong and conductive gel that bonds tightly with the surface it’s attached to. “It’s a very simple process,” Yuk says.

The bonding proves to be highly resistant to bending, twisting, and even folding of the substrate material. The adhesive polymer has been tested in the lab under accelerated aging conditions using ultrasound, but Yuk says that for the biomedical device industry to accept such a new material will require longer, more rigorous testing to confirm the stability of these coated fibers under realistic conditions over long periods of time.

“We’d be very happy to license and put this technology out there to test it further in realistic situations,” he says. The team has begun talking to manufacturers to see “how we can best help them to test this knowledge,” he says.

“I think this is a great piece of work,” says Zhenan Bao, a professor of chemical engineering at Stanford University, who was not associated with this research. “Wet adhesives are already a big challenge. Conductive adhesives that work well in wet conditions are even more rare. They are very much needed for nerve interfaces and recording electrical signals from the heart or brain.”

Bao says this work “is a major advancement in the bioelectronics field.”