For more than three centuries scientists have believed that human sperm swim by swishing their tails in a side-to-side, symmetrical motion. But that’s because we’ve been looking at them with 2D microscopes.
Using state-of-the-art 3D microscopy, a piezoelectric device, and mathematics, researchers in Mexico discovered how sperm really move: They spin, with a wonky asymmetrical wiggle. The researchers reported their discovery today in the journal Science Advances.
In Maryland, restaurant patrons stand inside bumper-style tables to keep six feet apart. In New York, sunbathers maintain distance by lounging in white chalk circles painted on a grassy field.
As the United States slowly begins opening public spaces, organizations are getting creative about how to encourage social distancing. But two new studies on the airborne spread of saliva droplets, which can harbor virus particles from respiratory diseases like COVID-19, suggest those six feet alone are not always enough.
When the last global pandemic broke out, in 1918, it ravaged a population with essentially no technological countermeasures. There were no diagnostic tests, no mechanical ventilators, and no antiviral or widely-available anti-inflammatory medications other than aspirin. The first inactivated-virus vaccines would not become available until 1936. An estimated 50 million people died.
For the current outbreak, a best-case scenario could limit fatalities to 1.3 million, according to projections by Imperial College London. That in a world with 7.8 billion people—more than four times as many as in 1918. Many factors will lessen mortality this time, chief among them better, more consistent implementation of social-distancing measures. But technology will also be a primary bulwark. Enormous sums are being spent to ramp up testing, diagnosis, modeling, treatment, vaccination, and other tech-based responses.
The COVID-19 epidemic in China was gathering terrible force when 11 overworked Chinese physicians found time to write a research paper. At the time, in mid February, confirmed cases of the disease were inching towards 60,000 and the death toll stood at nearly 1,400. The doctors, most of them pulmonary specialists at the Xi’an Chest Hospital, had already treated scores of people seriously stricken with the disease.
Weary as they were, they had something they wanted to tell the world: “Ultrasound is playing an indispensable role in the diagnosis, treatment and efficacy evaluation of severe acute pneumonia,” the life-threatening illness associated with the most severe cases of COVID-19.
Over the past week, companies around the world announced a flurry of AI-based systems to detect COVID-19 on chest CT or X-ray scans. Already, these deep learning tools are being used in hospitals to screen mild cases, triage new infections, and monitor advancing disease.
AI-powered analysis of chest scans has the potential to alleviate the growing burden on radiologists, who must review and prioritize a rising number of patient chest scans each day, experts say. And in the future, the technology might help predict which patients are most likely to need a ventilator or medication, and which can be sent home.
I remember a faded yellow booklet, about the size of a wallet, that my mother used to pull out once a year at the doctor’s office to record my vaccines. Today, nurses document my children’s vaccination history in electronic health records that will likely follow them to adulthood.
To eradicate a disease—such as polio or measles—healthcare workers need to know who was vaccinated and when. Yet in developing countries, vaccination records are sparse and, in some cases, non-existent. For example, during a rural vaccination campaign, a healthcare worker may mark a child’s fingernail with a Sharpie, which can wash or scrape off within days.
Now, a team of MIT bioengineers has developed a way to keep invisible vaccine records under the skin. Delivered through a microneedle patch, biocompatible quantum dots embed in the skin and fluoresce under near-infrared light—creating a glowing trace that can be detected at least five years after vaccination. The work is described today in the journal Science Translational Medicine.
The wonder crystal could yield imagers that are far more sensitive than commercial detectors
The crystalline material known as perovskite makes for a superefficient photovoltaic cell. Researchers are also exploring perovskites’ potential in transistors and LED lighting. But there’s yet another use for this wonder crystal, and it may be the most promising of all: as X-ray detectors.
Dozens of groups around the world are exploring this area, and major X-ray imaging manufacturers, including Samsung and Siemens, are considering perovskite for their next-generation machines. Compared with today’s X-ray imagers, detectors based on perovskite compounds are far more sensitive and use less power. And for certain applications, the materials can be tuned to emit color when irradiated. Lab prototypes of imagers that use perovskite have been demonstrated to be at least 100 times as efficient as their conventional counterparts.
“Interest in perovskite crystals for imaging emerged out of all the recent enthusiasm to get better solar panels,” says I. George Zubal, director of the nuclear medicine and computed tomography programs at the National Institute of Biomedical Imaging and Bioengineering (NIBIB), in Bethesda, Md. His program funds research into new imaging devices, procedures, and software, including groups looking at perovskite X-ray detection.
What makes perovskites so useful for X-ray detection is the same thing that makes them good for solar cells: They’re excellent at converting light into electrical charge. In a direct detector, X-ray photons are converted into electrons inside a semiconductor. In a scintillator imager, the X-ray photons are first converted into visible light, which is then converted into electrons by a photodiode array.
Conventional direct X-ray detectors have higher resolution than do scintillators, but they take longer to acquire an image. That’s because the semiconductor material they typically use—amorphous selenium—isn’t great at stopping X-rays. Scintillator imagers, on the other hand, are more sensitive than direct X-ray imagers—meaning you need fewer X-rays to create the image—but yield a lower-quality image.
Perovskites could be the answer to the main shortcomings of current X-ray imagers, says Zubal. “Perovskite stops a lot more of the X-rays [compared to amorphous selenium], and being a semiconductor it should give us higher-resolution images, showing the small structures of objects…. You’re also lowering the radiation dose to the patient, which is another main reason for the NIBIB’s enthusiasm.”
In one experiment, Xiaogang Liu’s group at the National University of Singapore started with a commercial flat-panel X-ray detector that used bulk scintillators of cesium iodide thallium. The group removed the CsI(TI) layer and replaced it with a layer of nanocrystals of cesium lead bromide—an inorganic perovskite—directly coating them onto photodiode arrays. When coupled with photomultiplier tubes, the resulting device had a detection limit that was just 1/400 that of medical X-ray machines, as the group reported in Nature last September. Several X-ray manufacturers are now testing nanocrystal scintillators using his group’s approach, Liu says.
Liu credits grad student Qiushui Chen for coming up with the idea of using perovskite nanocrystals in this way. “A lot of our recent work involves rare-earth materials, which is what conventional scintillators use,” Liu says. To form the perovskite layer, the researchers mixed the nanocrystals with liquid cyclohexane and then spin-coated the mixture onto a flexible substrate.
“We got a little bit lucky, because we discovered that the nanocrystals had to be deposited on the substrate through a solid-state process,” Liu says. “If the particles are dispersed in solution, it’s no good.”
Researchers have also demonstrated perovskites in direct X-ray detectors with vastly superior performance to that of commercial imagers. In general, says the NIBIB’s Zubal, direct X-ray detectors are “highly more desirable” than scintillators because they avoid the extra step of converting visible light into electrons. The projects that NIBIB is supporting involve direct detection.
Jinsong Huang and his group at the University of North Carolina at Chapel Hill have been studying direct X-ray detectors based on perovskites since 2014. (Huang also works on perovskite photovoltaics.) In one experiment, they coated methylammonium lead tribromide—a common perovskite compound—onto a regular X-ray detector that used amorphous silicon to convert the X-rays to electrons. The addition of the perovskite layer made it 3,000 times as sensitive.
“When you want extremely efficient and sensitive detectors, you need to count single photons, and that’s not easy,” Huang explains. “We showed that we can make materials that allow you to distinguish the signal from the noise.” Huang recently created a startup to commercialize radiation detectors based on his group’s work.
There are still a number of hurdles to cross before perovskite scintillators or direct X-ray imagers will be ready for market. A big obstacle is that some perovskites are sensitive to moisture. Liu has developed a method for coating each nanocrystal with silicon dioxide and is exploring other protective methods. Perovskite layers can also be encapsulated in glass, much like traditional solar cells are.
But in general, perovskite X-ray imagers won’t need to be quite as hardy as perovskite PVs or LEDs, because the environmental conditions they’ll face are more benign. Solar panels need to perform even after being exposed to the elements for 20 years, while LEDs are exposed to heat and, of course, light, both of which can degrade a perovskite compound. X-ray machines, by contrast, are typically used in climate-controlled settings. For that reason, Liu and Huang believe perovskite X-ray detectors will be commercialized much more quickly than other perovskite applications.
Huang predicts that perovskite detectors will open up new applications for X-rays, expanding what’s already a multibillion-dollar industry. More efficient imagers would draw less power, lending themselves to portable machines that run on batteries. Liu’s group has also demonstrated a variety of tunable, color-emitting perovskite nanocrystals. That work could lead to multicolor X-ray displays, which are impossible with today’s scintillator X-ray machines.
And because they use flexible substrates, perovskite imagers could conform to whatever’s being scanned; anyone who has experienced the discomfort of a mammogram will appreciate that feature. Faster, more sensitive imagers would also reduce the radiation from dental and medical X-rays and airport security scanners.
“Once we can make X-rays much safer, the market will change because you’ll be able to put the detectors everywhere,” Huang says.
A University of Maryland-developed microscopy technique could eliminate the “surgery” aspect of LASIK
Fischell Department of Bioengineering (BIOE) researchers have developed a microscopy technique that could one day be used to improve LASIK and eliminate the “surgery” aspect of the procedure. Their findings were published in March in Physical Review Letters.
In the 20 years since the FDA first approved LASIK surgery, more than 10 million Americans have had the procedure done to correct their vision. When performed on both eyes, the entire procedure takes about 20 minutes and can rid patients of the need to wear glasses or contact lenses.
While LASIK has a very high success rate, virtually every procedure involves an element of guesswork. This is because doctors have no way to precisely measure the refractive properties of the eye. Instead, they rely heavily on approximations that correlate with the patient’s vision acuity—how close to 20/20 he or she can see without the aid of glasses or contacts.
In search of a solution, BIOE Assistant Professor Giuliano Scarcelli and members of his Optics Biotech Laboratory have developed a microscopy technique that could allow doctors to perform LASIK using precise measurements of how the eye focuses light, instead of approximations.
“This could represent a tremendous first for LASIK and other refractive procedures,” Scarcelli said. “Light is focused by the eye’s cornea because of its shape and what is known as its refractive index. But until now, we could only measure its shape. Thus, today’s refractive procedures rely solely on observed changes to the cornea, and they are not always accurate.”
The cornea—the outermost layer of the eye—functions like a window that controls and focuses light that enters the eye. When light strikes the cornea, it is bent—or refracted. The lens then fine-tunes the light’s path to produce a sharp image onto the retina, which converts the light into electrical impulses that are interpreted by the brain as images. Common vision problems, such as nearsightedness or farsightedness, are caused by the eye’s inability to sharply focus an image onto the retina.
To fix this, LASIK surgeons use lasers to alter the shape of the cornea and change its focal point. But, they do this without any ability to precisely measure how much the path of light is bent when it enters the cornea.
To measure the path light takes, one needs to measure a quantity known as the refractive index; it represents the ratio of the velocity of light in a vacuum to its velocity in a particular material.
By mapping the distribution and variations of the local refractive index within the eye, doctors would know the precise degree of corneal refraction. Equipped with this information, they could better tailor the LASIK procedure such that, rather than improved vision, patients could expect to walk away with perfect vision—or vision that tops 20/20.
Even more, doctors might no longer need to cut into the cornea.
“Non-ablative technologies are already being developed to change the refractive index of the cornea, locally, using a laser,” Scarcelli said. “Providing local refractive index measurements will be critical for their success.”
Knowing this, Scarcelli and his team developed a microscopy technique that can measure the local refractive index using Brillouin spectroscopy—a light-scattering technology that was previously used to sense the mechanical properties of tissue and cells without disrupting or destroying either.
“We experimentally demonstrated that, by using a dual Brillouin scattering technology, we could determine the refractive index directly, while achieving three-dimensional spatial resolution,” Scarcelli said. “This means that we could measure the refractive index of cells and tissue at locations in the body—such as the eyes—that can only be accessed from one side.”
In addition to measuring corneal or lens refraction, the group is working on improving its resolution to analyze mass density behavior in cell biology or even cancer pathogenesis, Scarcelli said.
Along with Scarcelli, BIOE Ph.D. student Antonio Fiore (first author) and Carlo Bevilacqua, a visiting student fromthe University of Bari Aldo Moro in Bari, Italy, contributed to the paper.
The collective thoughts of the interwebz
The cookie settings on this website are set to "allow cookies" to give you the best browsing experience possible. If you continue to use this website without changing your cookie settings or you click "Accept" below then you are consenting to this.