The study was led by Dr. Mathilde Touvier, a research director at INSERM (the French National Institute for Health and Medical Research), and Anaïs Hasenböhler, PhD student, both from the Nutritional Epidemiology Research Team at the Université Sorbonne Paris Nord and Université Paris Cité, France.

Preservatives are added to foods for several reasons, including preventing the growth of bacteria and mold, slowing spoilage, and helping products maintain their color, flavor, or freshness for longer. Because these ingredients are so widely used, researchers wanted to better understand whether long-term exposure could be connected to cardiovascular health.

Ms. Hasenböhler said: “Food preservatives are used in hundreds of thousands of industrially processed foods. Experimental studies suggest that some preservative food additives may be harmful to cardiovascular health, but we have not had enough evidence on the impact of these ingredients in humans. As far as we know, this is the first study of its kind to investigate the links between a wide range of preservatives and cardiovascular health.”

Tracking Diet and Heart Health in More Than 112,000 People

The work was conducted as part of NutriNet-Santé, a large ongoing research project examining the connections between nutrition and health. The analysis included 112,395 volunteers living across France.

Every six months, participants recorded everything they ate and drank during a three-day period. This gave researchers unusually detailed information about their diets rather than relying only on broad estimates of food consumption.

The research team then examined the ingredients in those foods and beverages, including the preservatives they contained. Participants were followed for an average of seven to eight years so researchers could track whether they developed high blood pressure or cardiovascular diseases such as heart attack, stroke, or angina.

Preservative exposure was nearly universal. During the first two years of participation, 99.5% of the volunteers consumed at least one food preservative.

Higher Preservative Intake Linked to Higher Risk

The strongest associations appeared among people consuming the largest amounts of certain preservatives.

Participants with the highest intake of ‘non-antioxidant’ preservatives had a 29% higher risk of hypertension than those consuming the lowest amounts. They also had a 16% higher risk of cardiovascular disease, which included heart attack, stroke and angina.

People who consumed the greatest amounts of antioxidant preservatives had a 22% higher risk of hypertension.

The two categories protect food in different ways. Non-antioxidant preservatives are generally used to prevent potentially harmful microorganisms, including bacteria and mold, from growing. Antioxidant preservatives instead slow oxidation, a chemical process that can cause foods to brown, develop unpleasant flavors, or become rancid.

Eight Common Preservatives Stood Out

Researchers also analyzed 17 of the preservatives most commonly consumed by participants.

Eight were specifically associated with a higher risk of high blood pressure: potassium sorbate (E202), potassium metabisulphite (E224), sodium nitrite (E250), ascorbic acid (E300), sodium ascorbate (E301), sodium erythorbate (E316), citric acid (E330) and extracts of rosemary (E392).

Ascorbic acid (E300) was also specifically associated with cardiovascular disease.

These findings do not mean that consuming one of these ingredients will necessarily cause high blood pressure or heart disease. The research was observational, meaning it identified statistical associations rather than proving that preservatives were directly responsible for the increased risks.

Dr. Touvier added: “This study has some limitations inherent to its observational design. However, the findings are based on highly detailed data, and we have taken account of other factors that can increase or lower the risk of cardiovascular disease. Experimental research in the literature consistently suggested that preservatives may cause oxidative stress in the body or affect the way the pancreas works.

“These results suggest we need a re-evaluation of the risks and benefits of these food additives by the authorities in charge, such as the EFSA in Europe and the FDA in the USA, for better consumer protection. In the meantime, these findings support existing recommendations to favor non-processed and minimally processed foods, and avoid unnecessary additives. Doctors and other healthcare professionals play a key role in explaining these recommendations to the public.”

Why Preservatives Might Affect the Body

One possible explanation involves oxidative stress. This occurs when reactive molecules build up faster than the body’s protective systems can neutralize them, potentially damaging cells and tissues over time.

Researchers are also investigating whether preservatives could influence pancreatic function. The pancreas plays a central role in regulating blood sugar and metabolism, so changes in its function could have broader effects throughout the body.

The team is now studying how food additives and ultra-processed foods may influence inflammation, oxidative stress, the metabolic profile of the blood, and the gut microbiota.

The gut microbiota refers to the enormous community of bacteria and other microorganisms living in the digestive tract. These microbes are increasingly being studied for their possible roles in metabolism, immune function, and cardiovascular health.

By examining these biological changes, researchers hope to better understand why exposure to certain additives may be associated with a higher risk of disease and whether the preservatives themselves are contributing to those effects.

He was not entirely sure he wanted to open it.

Schlamminger, a physicist at the National Institute of Standards and Technology (NIST), had spent much of the previous decade trying to measure the universal gravitational constant. Known to physicists as big G, this fundamental number determines the strength of gravitational attraction throughout the universe.

The number hidden in the envelope was the key that would finally unscramble his experimental data and reveal what his team had measured.

Gravity’s Most Elusive Number

Gravity is one of the most familiar forces in everyday life. It keeps people anchored to Earth, guides planets around the Sun, helps gather stars into galaxies, and plays a central role in shaping the enormous cosmic web of galaxy clusters that stretches across the universe.

Yet scientists still do not know its fundamental strength with the precision they have achieved for other basic forces of nature.

That strength is represented by big G.

Scientists have been attempting to measure big G for more than 225 years, beginning roughly a century after Isaac Newton introduced his law of universal gravitation. Despite generations of increasingly sophisticated experiments, the gravitational constant remains less precisely known than comparable constants associated with nature’s other three fundamental forces: electromagnetism and the strong and weak nuclear forces.

Part of the problem is surprisingly simple. Gravity is extraordinarily weak.

A tiny magnet can demonstrate the problem. A magnet roughly the size of a pinhead can lift a paper clip against the gravitational pull of the entire Earth. In that simple contest, the electromagnetic force produced by the magnet easily overcomes gravity.

The challenge becomes even greater in the laboratory. Scientists cannot move planets around to perform controlled experiments, so they have to measure the gravitational attraction between much smaller objects that can be weighed and precisely positioned.

Those experimental masses are about 500 billion trillion times smaller than Earth. As a result, the gravitational forces researchers are trying to detect are incredibly faint.

Measurements That Refuse to Agree

Modern instruments have become extraordinarily sensitive, but measurements of big G continue to produce slightly different answers.

The disagreements are small, roughly one part in 10,000. Yet they are still larger than researchers would expect from ordinary experimental uncertainty.

That persistent mismatch has created an uncomfortable question for physicists.

The most likely explanation is that some subtle experimental effect has been overlooked. But there is also a far more intriguing possibility: Perhaps scientists are missing something about gravity itself.

Schlamminger and his colleagues hoped to clarify the problem by carefully replicating a precision experiment carried out by the International Bureau of Weights and Measures (BIPM) in Sèvres, France, in 2007.

The idea was straightforward. If an independent team at NIST’s campus in Gaithersburg, Maryland, could reproduce the French measurement using essentially the same approach, it could help resolve the disagreement surrounding big G.

But Schlamminger was concerned about another source of error: himself.

Scientists can unintentionally influence how they interpret or analyze measurements when they know what answer they expect. Schlamminger wanted to eliminate that possibility as much as possible.

So he asked colleague Patrick Abbott to blind the experiment by scrambling part of the data.

Abbott subtracted a secret number from the carefully measured weights of some of the masses used in the experiment. Because only Abbott knew that number, Schlamminger could analyze the experiment without knowing the true value of big G his team was producing.

The correction needed to recover the real answer was sealed inside an envelope.

Ten Years of Work Came Down to One Envelope

Schlamminger nearly opened the envelope in 2022.

At the last moment, however, he realized that the team had not fully accounted for a subtle effect involving air pressure. Because even tiny disturbances can matter in an experiment this sensitive, he postponed the reveal and returned to the analysis.

Two years later, the moment finally arrived.

At 3 p.m. on July 11, 2024, Schlamminger was scheduled to present the results at the annual Conference on Precision Electromagnetic Measurements in Aurora, Colorado.

He was so anxious that he skipped the morning sessions. Instead, he mentally revisited the many things that could have distorted the measurement, including small variations in temperature and pressure.

By then, he believed the team had accounted for everything it reasonably could.

“I had really dotted all the i’s and crossed all the t’s of the experiment,” he said.

During his afternoon presentation, Schlamminger finally revealed the hidden number.

He immediately felt relieved.

For the experiment to produce the result he anticipated, Abbott’s secret correction needed to be relatively large and negative.

It was.

At first, that seemed like good news.

But as the day went on, Schlamminger realized there was a problem. The correction was too large. Once the blinded data were restored, the NIST measurement did not agree with the French result.

A Tiny Difference With Big Implications

After another two years of detailed analysis, Schlamminger and his collaborators reported their measurement in Metrologia.

Their value for G was 6.67387 × 10^-11 meters³/kilogram/second².

That result is 0.0235% lower than the value obtained in the French experiment.

In ordinary life, a difference that small would be meaningless. It will not noticeably change the reading on a bathroom scale, and it would not affect how much peanut butter is required to produce a 16-ounce container.

For fundamental physics, however, the discrepancy is significant.

Other fundamental constants of nature are known to six or more significant digits. Big G remains stubbornly less precise.

History also gives physicists a reason to pay attention to tiny discrepancies. On several occasions, small mismatches between measurements and expectations have eventually revealed that scientists were missing something important about how nature works.

That does not mean the disagreement over big G points to new physics. Experimental error remains the more likely explanation. But the continued inability of precision experiments to converge on the same value keeps the mystery alive.

An Experiment With Roots in 1798

The technique used by both the BIPM and NIST teams has a history stretching back more than two centuries.

Their experiments relied on a torsion balance, an instrument capable of detecting extremely small forces by measuring how much a thin suspended fiber twists.

The basic idea dates to a famous experiment performed by English physicist Henry Cavendish in 1798.

Cavendish placed two lead balls at opposite ends of a wooden beam suspended horizontally from its center by a thin wire. He then positioned two much heavier masses nearby.

The heavier masses gravitationally attracted the smaller lead balls, causing the suspended beam to rotate. As the beam turned, the wire twisted until its resistance balanced the gravitational pull.

By measuring the tiny movement of the beam with a mirror and a light pointer, Cavendish could determine the gravitational interaction between the masses and obtain information corresponding to the value of big G.

More than 200 years later, the same basic principle remains useful, although the equipment has become vastly more sophisticated.

Measuring a Force Almost Too Small to See

The BIPM and NIST experiments used eight cylindrical metal masses.

Four larger cylinders were positioned on a rotating carousel in a configuration resembling four candlesticks on an old-fashioned chandelier. Four smaller masses were located inside the carousel on a disk suspended from a copper-beryllium ribbon about as thick as a human hair.

Gravity between the outer and inner masses caused the suspended torsion balance to rotate, twisting the thin metal ribbon.

By precisely measuring that motion and the associated gravitational torque, the researchers could calculate one value for G. Torque is simply a twisting force, similar to the force used when turning a wrench.

But the teams did not rely on only one method.

In another series of measurements, the scientists placed electrodes beside the inner masses and applied electrical voltage to them.

The resulting electrostatic force produced torque in the opposite direction from the gravitational torque.

Researchers then adjusted the voltage until the electrostatic effect exactly balanced the gravitational effect, preventing the torsion balance from turning.

Because the amount of voltage required to achieve that balance could be measured with exceptional precision, it provided another way to calculate big G.

Copper and Sapphire Give the Same Answer

Schlamminger’s team introduced an additional test.

They wanted to know whether the material used for the experimental masses could somehow influence the result.

The researchers first performed the measurements using copper masses. Then they repeated the experiment using sapphire.

The outcome was essentially the same with both materials.

That result eliminated one possible explanation for the discrepancy, but it did not solve the larger mystery.

After a decade of work, the NIST experiment has become another important data point in scientists’ continuing effort to determine the true value of big G.

“Every measurement is important, because the truth matters,” Schlamminger said. “For me, making an accurate measurement is a way of bringing order to the universe, whether or not the number agrees with the expected value,” he added.

After devoting years to the problem, Schlamminger says he is ready to hand the challenge to others.

“I’ll leave it to younger generations of scientists to work on the problem,” he added.

“We must press on.”

Big G Is Not the Same as Little g

Big G is not the only letter g associated with gravity.

Physicists also use little g, but the two quantities describe very different things.

Little g refers to the acceleration an object experiences because of the gravitational attraction of a nearby large body such as Earth.

Unlike big G, little g changes depending on where you are.

Near Earth’s surface, little g is approximately 9.8 meters per second squared. On the Moon, it is only about 1.62 meters per second squared because the Moon has much less mass and therefore produces weaker gravitational acceleration.

Big G, in contrast, is considered universal.

To the best of scientists’ knowledge, it has the same value everywhere in the cosmos. It determines the gravitational force between any two objects, whether those objects are two laboratory masses, a person and Earth, or two astronomical bodies separated by enormous distances.

Newton’s law of gravitation uses big G to connect mass, distance, and gravitational force.

For two masses, m₁ and m₂, scientists multiply the masses together, divide that result by the square of the distance r between them, and then multiply by big G.

Written mathematically, the relationship is:

Gm₁m₂/r²

More than two centuries after scientists began trying to measure it precisely, that seemingly simple constant remains one of the most difficult numbers in physics to pin down.

In a review article published in the New England Journal of Medicine, Boston University professor Nancy Sullivan argues that outbreak preparedness needs to extend beyond the infectious diseases that receive the most attention.

A Rare Relative of Ebola

Bundibugyo belongs to the filovirus family, the same group of viruses that includes the much better-known Ebola virus. Despite its potential severity, Bundibugyo has been linked to only two previously recognized outbreaks, one in Uganda in 2007 and another in the Democratic Republic of Congo (DRC) in 2012.

The current outbreak, however, has already surpassed those earlier events in both its trajectory and scale. According to the WHO, 695 confirmed cases and 138 confirmed deaths had been reported in the DRC and Uganda as of June 11.

Sullivan, a professor of biology and virology, immunology & microbiology at Boston University, explains that bringing an outbreak under control depends on several measures working quickly together. These include rapid diagnosis, isolating infected patients, tracing people who may have been exposed, strengthening infection control, and providing supportive medical care.

Those steps become much harder when laboratory resources are limited. In settings where testing capacity is scarce, delays in confirming infections can give the virus more time to spread.

A Severe Hemorrhagic Fever

Bundibugyo can cause a severe form of hemorrhagic fever. Infection can trigger widespread inflammation, damage and failure of the cells lining blood vessels, uncontrolled bleeding, and failure of multiple organs.

The virus spreads through direct contact with infected bodily fluids. That creates particular risks for family members, caregivers, and health workers, especially when patients are being treated in hospitals without adequate infection control. The 2026 outbreak was formally recognized after the death of a nurse.

Another major challenge is that Bundibugyo can initially resemble several far more common illnesses. Symptoms overlap with malaria, typhoid fever, and other diseases, meaning laboratory testing is necessary to confirm an infection.

Testing Delays Can Slow the Response

Laboratory access remains limited in parts of the DRC, Sullivan found, and samples may need to travel considerable distances to reach national reference laboratories. That can turn a critical diagnosis into a lengthy process.

“Delays in specimen collection, transportation and testing can postpone confirmation by days or weeks, which hinders the isolation of infected persons, contact tracing and the initiation of outbreak-control measures,” Sullivan wrote.

Those delays can be especially damaging during an outbreak, when identifying cases quickly is essential for separating infected people from others and finding anyone who may have been exposed.

The Risk of Overlooking Rare Viruses

The Bundibugyo outbreak also points to a larger weakness in preparedness strategies that concentrate heavily on the most familiar high-risk pathogens.

For decades, Bundibugyo caused relatively little recognized activity. Its return as a significant threat illustrates how difficult it can be to predict which infectious disease will drive the next major outbreak.

Sullivan has argued that medical countermeasures should be developed more broadly for pathogens capable of causing severe illness or death in humans, rather than focusing only on viruses already known to cause frequent outbreaks.

No Licensed Bundibugyo Vaccine

Considerable progress has been made toward vaccines and other medical countermeasures for the Ebola, Sudan and Marburg viruses. Bundibugyo, however, occurs much less often, and no licensed vaccine or therapeutic has been developed specifically to target it.

There are encouraging signs that vaccines designed against other virus species could offer at least some protection, but Bundibugyo remains an example of a dangerous pathogen for which dedicated medical tools are limited.

Sullivan says preparedness also needs to involve much more than creating diagnostic tests, vaccines and drugs. Health systems must be capable of coordinating quickly when outbreaks spread across borders.

“Preparedness planning should extend beyond diagnostics, vaccines, and therapeutics to include operational readiness for multinational outbreak response,” she said.

Now that passion has earned him an unusual scientific honor. Researchers have named a newly identified snake species from New Guinea Lielaphis slashi, or Slash’s groundsnake.

“As a long time herpephile, I am extremely honored and humbled to have Lielaphis slashi from New Guinea named after me. It is really exciting, I never would have imagined this moment would arrive,” says Slash.

A Childhood Connection to Slash

For Sara Ruane, the Field Museum’s Associate Curator of Herpetology and senior author of a paper in Zootaxa describing the species, the name also has a personal connection.

“Guns N’ Roses has been one of my favorite bands since I was in first grade, and by fifth grade, I had already told my teacher that I wanted to be a herpetologist — a scientist who studies reptiles — when I grew up,” says Sara Ruane, the Field Museum’s Associate Curator of Herpetology and senior author of a paper in Zootaxa describing the new species. “So when I was twelve years old and got my copy of Reptiles Magazine in the mail and it had a picture of Slash holding his pet reticulated python on the cover, I thought, ‘This guy is so cool.'”

Years later, after Ruane became a scientist who sometimes has the opportunity to assign official names to newly recognized reptile species, she returned to that old magazine interview.

“I reread his interview, and he talked about how much he loves museums and zoos and natural history, and about how when he was a kid, he’d go outside and look for snakes — it was all stuff that I really related to, and it made me think that he’d be a great person to name a new species after,” says Ruane.

Her opportunity eventually came in the form of a reddish-brown snake measuring 28 inches long that had been collected in the forests of New Guinea.

A Mysterious Snake From New Guinea

New Guinea is the world’s second-largest island, behind Greenland. Located just north of Australia, the island is divided between Indonesia and Papua New Guinea. Its tropical forests support enormous biological diversity, much of which remains poorly documented by scientists.

During fieldwork one night in 2006, Chris Austin, a professor and curator of herpetology at the Louisiana State University Museum of Natural Science, encountered a snake in New Guinea that he did not recognize.

“These New Guinea groundsnakes are nocturnal, so the best way to find them is at night. They are typically found just after sunset at the base of large trees where they are looking for something to eat,” says Austin, a co-author of the paper describing the new species. “When working at night in New Guinea you need to be very careful as there are several highly venomous species that look very similar to the non-venomous groundsnakes.”

After completing her doctorate, Ruane worked with Austin at LSU in 2016. The two began collaborating to better understand New Guinea’s poorly studied snakes, and they have continued working together on the group ever since.

Genetics Reveal a New Species

At first glance, the snake did not obviously appear to represent a species new to science. Laboratory work, however, revealed important differences.

“Using multiple cutting-edge genetic analyses, we found that L. slashi is genetically distinct from other similar snakes in the same genus,” says Tianqi Huang, the study’s first author and a post-doctoral researcher at the Field Museum with Ruane. “The combination of physical characteristics, like differences in numbers of scales when compared with other species, and the genetic evidence is what led us to realize that it is an entirely new species. We also used ecological modeling to show that L. slashi‘s preferred habitat is different from similar snakes.”

The researchers combined genetic evidence with physical traits, including differences in scale counts, to distinguish L. slashi from related snakes. Ecological modeling also indicated that the new species favors a different type of habitat than similar members of the genus.

What Slash’s Groundsnake Eats

Scientists still know relatively little about the behavior and ecology of Slash’s groundsnake.

“It’s incredibly hard to observe snakes in the wild before they slither away, so our knowledge about L. slashi is limited,” says Ruane.

Its anatomy does provide some hints about how it may live and feed.

“Snakes in this genus often have large teeth in the back of their mouths, which New Guinea groundsnakes may use to grab on to and eat small, slippery-scaled lizards and the eggs of other reptiles; this snake isn’t grasping and squeezing its prey like a boa constrictor,” says Ruane.

Although Guns N’ Roses has been called the “most dangerous band in the world,” its reptilian namesake is not dangerous to people. L. slashi does not produce venom capable of seriously harming a human.

Threats to New Guinea’s Forests

Slash’s groundsnake may pose little danger to humans, but human activity could threaten the species and many other animals living in New Guinea’s forests.

“The habitats that Slash’s groundsnake is from are under threat from industries like coffee farming and mining,” says Ruane. “That’s part of why describing the species that live there is important. Every species should be recognized in order for us to better understand how ecosystems work, how everything fits into the environment. We can’t conserve animals or other living things that we don’t know about.”

By formally identifying species such as L. slashi, scientists can build a clearer picture of New Guinea’s biodiversity and better understand which organisms may be at risk as their habitats change.

This study was contributed to by Tianqi Huang (Field Museum and Rutgers University), Chris Austin (Louisiana State University Museum of Natural Science), Justin Bernstein (Slippery Rock University and the American Museum of Natural History), Bulisa Iova (Papua New Guinea National Museum and Art Gallery), Jackson Roberts (Virginia Museum of Natural History), Jeffrey Frederick (University of Kentucky), and Sara Ruane (Field Museum).

Caltech researchers have now developed a device that uses one beam of light to redirect another in just 74 femtoseconds (74 quadrillionths of a second). That is roughly the amount of time light needs to travel across the width of a human hair.

“Steering light with light is very challenging because light typically interacts very weakly with matter. Using optical meta-surfaces (ultrathin carefully nanoengineered sheets), we can up the interaction strength to make this possible with much higher efficiency,” says Harry Atwater, the Howard Hughes Professor of Applied Physics and Materials Science and the Otis Booth Leadership Chair of the Division of Engineering and Applied Science at Caltech.

The researchers report their findings in a paper recently published in Nature Nanotechnology. Lead author Claudio Hail carried out the research while he was a postdoctoral scholar in Atwater’s Caltech lab. He is now an assistant professor of mechanical engineering at UC Berkeley.

Why Conventional Light Steering Has a Speed Limit

Many existing technologies for steering or modulating light depend on changing the electronic properties of a material. Examples include liquid-crystal panels used in projectors and optical chips found in telecommunications systems.

In these devices, electrons are pushed into higher energy states before returning to lower ones and releasing their excess energy. That relaxation takes time, creating a bottleneck that usually limits light modulation to nanosecond or picosecond timescales (trillionths of a second).

Atwater’s team took a different approach by eliminating the need for an electrical signal. Instead, the researchers used a powerful beam of light, known as the pump, with a carefully designed pattern that temporarily altered the optical behavior of a material.

A second, weaker beam, called the probe, then passed through that material. Its direction changed according to the pattern created by the pump beam.

Using the Optical Kerr Effect

The system relies on a phenomenon known as the optical Kerr effect. When an intense beam of light passes through a material, it can briefly produce a very small change in the material’s refractive index, which describes how much light slows down and bends as it travels through that material.

The effect comes from changes in the motion of electrons within their orbitals, regions around an atom’s nucleus where electrons have a high probability of being located. Crucially, the electrons are not pushed into separate, longer-lasting excited states.

As a result, the change can appear and vanish almost as quickly as the light pulse itself. There is no need to wait for excited electrons to fall back to lower energy levels.

On its own, though, the optical Kerr effect is too weak to redirect a beam of light by an amount that would be useful in practical devices.

Nanoscale Silicon Pillars Amplify the Effect

To strengthen the response, the researchers created a meta-surface from a thin film of amorphous silicon. The surface was covered with nanoscale pillars, each smaller than the wavelength of the pump’s light.

By carefully choosing the size and spacing of these pillars, the team caused light to remain inside the meta-surface slightly longer and circulate within it instead of simply passing straight through.

That additional interaction time amplified the small refractive index change in the silicon. The resulting effect became strong enough to redirect the probe beam.

Using this design, the researchers steered light by angles of up to 13 degrees in as little as 74 femtoseconds. They also showed that the modulation speed was limited by the duration of the pump pulse (which was also 74 femtoseconds).

Even Faster Light Control May Be Possible

The researchers say the current speed limit comes from the laser pulses used to operate the system, not from the fundamental properties of the meta-material itself.

That leaves open the possibility of making the process even faster. With further development, the technology could reach timescales relevant to emerging photonic concepts including time crystals and synthetic time-varying optical materials.

The paper is titled “Ultrafast, reconfigurable all-optical beam steering and spatial light modulation.” Along with Hail and Atwater, Lior Michaeli is also an author of the paper. He completed the work as a postdoctoral scholar at Caltech and is now an assistant professor of electrical and computer engineering at Tel Aviv University.

The work was supported by funding from the Air Force Office of Scientific Research and its Meta-Imaging Multidisciplinary University Research Initiative, the Swiss National Science Foundation, the Fulbright Fellowship program, and the Breakthrough Foundation. The Kavli Nanoscience Institute at Caltech provided infrastructure and support for the work.