When Deblina Sarkar wanted to name her lab’s new creation the “Cell Rover”, her students hesitated. “They were like, ‘this sounds too cool for a science tech,'” she says. But Sarkar, a nanotechnician at the Massachusetts Institute of Technology, wanted the name of the small device to evoke the exploration of unknown worlds. This rover, however, will roam the interior of a living cell rather than the surface of a planet.
Recent technical advances have allowed scientists to scale down electronics to the cellular scale, hoping to potentially use them to explore and manipulate the insides of individual cells. But such a rover would need to receive instructions and transmit information, and communicating with such small devices can be extremely difficult. “Miniaturizing an antenna to fit inside the cell is a major challenge,” says Sarkar. The problem concerns the electromagnetic waves that are used with most conventional antennas, such as those of cell phones, to transmit and receive data. Antennas work best at their so-called “resonant frequencies”, which occur at wavelengths roughly equal to the actual length of the antenna. Due to the mathematical relationship between the speed, frequency and wavelength of a wave, waves with shorter wavelengths have higher frequencies. Unfortunately, subcellular antennas must be so small that they require frequencies in the microwave range. And like the beams in a kitchen microwave, these signals “just fry the cells,” Sarkar says. But she and her colleagues think they have a solution. In a Nature Communication paper, they describe a new antenna design that can operate safely inside cells by resonating with acoustic rather than electromagnetic waves. A working antenna could help scientists power and communicate with tiny roving sensors inside the cell, helping them better understand these building blocks and perhaps leading to new medical treatments.
Sarkar and his team machined their experimental antenna from “magnetostrictive” material, a material that changes shape when exposed to a magnetic field. The researchers chose a widely available alloy of iron, nickel, boron and molybdenum, a combination already used in other types of sensors. When an alternating current magnetic field is applied to this magnetostrictive antenna, the north and south poles of its molecules align with the changing magnetic field, oscillating back and forth, which stretches the material. This movement causes the antenna to vibrate like a tiny tuning fork. Like any magnetic material, the antenna produces its own magnetic field in response to the external magnetic field, but as it vibrates, its movement changes its new magnetic field in a way that a receiver can detect. This allows two-way communication.
The main difference between a conventional antenna and the Cell Rover is the translation of electromagnetic waves into acoustic waves. “Their antenna resonates based not on the wavelength of light, but on the wavelength of sound,” says Jacob Robinson, a neuroengineer at Rice University who was not involved in the study. . Like larger traditional antennas, the Cell Rover reaches its resonant frequency when waves have a wavelength equal to its length, but the waves that boost this frequency are sound waves, which travel much slower than waves. electromagnetic. Since the relationship between wavelength and frequency of a wave also depends on its speed, sound waves and electromagnetic waves of the same wavelength will have different frequencies. In other words, the external magnetic field can signal the Cell Rover using waves with frequencies outside the range of harmful microwaves. “It’s a smart approach,” says Robinson.
The researchers first tested the Cell Rover in air and water, and they found that the antenna’s operating frequency was 10,000 times lower than that of an equivalent electromagnetic antenna, low enough to avoid killing living cells. The team then tested the device in a living system: the egg cell of the African clawed frog, a model organism. Since the Cell Rover was made from a magnetic material, researchers could use a magnet to pull it through each test cell. After these insertions, the eggs appeared healthy under the microscope and had not caused any leakage. Inside the egg, the Cell Rover was able to receive an electromagnetic transmission and send a response signal outward, up to a distance of one centimeter. The researchers also added several cellular rovers of different sizes to a single cell and found that they could distinguish transmission signals from individual rovers.
Despite the progress made in downscaling the Cell Rover, the prototypes themselves were still relatively large. At just over 400 micrometers (0.4 millimeters) long, they were too big to fit in many cell types. The scientists therefore simulated by calculation the operation of an antenna approximately 20 times smaller than those they tested. They found that these hypothetical rovers could maintain a similar communication range, but they haven’t built them yet. Robinson says the range will also need to be increased to allow these devices to work in living organisms. “I think more work needs to be done to add functionality,” adds Robinson. “They’re not doing anything biologically relevant yet.”
So far, scientists have only shown that the Cell Rover can work in principle, using it to send empty signals; this type of transmission can be considered a bit like static on a television. Then they will try to figure out what kind of “shows” they can watch by equipping the rover with tiny instruments that could collect and transmit information about the rover’s surroundings. For example, they could add a simple polymer coating that would bind to nearby ions or proteins. When these substances adhere to the polymer, they change the mass of the Cell Rover, which in turn changes the acoustic vibrations it produces. By measuring these changes, researchers could assess a cell’s protein or ion levels.
A Cell Rover can also be adapted to more complex applications. It may be possible to one day use such devices to destroy cancer cells, to electrically alter signaling pathways to influence cell division or differentiation, or even to serve as a power source for other devices. miniatures. “We can not only perform intracellular sensing and modulate intracellular activities, but we can also power nanoelectronic circuits,” says Sarkar. Such tiny electronics could also guide the Cell Rover on an exploratory journey, like its much larger namesakes: they would allow it to analyze sensor data and alter the cellular environment without the intervention of a scientist. “He will one day be able to make autonomous decisions,” says Sarkar. “The opportunities are simply limitless.”
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