Newly developed magnetic nanoparticles can be used to remotely control the behavior of ion channels, nerve cells and even animals. American physicists have now demonstrated in experiments that this works. As they report in “Nature Nanotechnology,” this technology could be used, for example, to stimulate brain cells in a targeted manner or to destroy specific proteins in tissues in cancer therapy.
Nanoparticles as Configurable Nanoprobes
They are just six nanometers in size, consist of a compound of iron, manganese and oxygen, and respond to a magnetic field in which they heat up. They can also be specifically configured to attach only to certain proteins in a cell membrane. And it is precisely this combination of properties that could make the nanoparticles now developed by a team of researchers at the University at Buffalo an ideal tool for medicine, as well as nanotechnology, in the future.
Because of their ability to target specific tissues and cell components, the particles act like tiny nanoprobes. And because they can be heated to around 34°C on command, stimulated only by an external magnetic field, they can have both stimulating and disruptive effects at their site of action. The researchers led by physicist Arnd Pralle demonstrated in several experiments that this works in practice.
Pain Receptor Switched on by Magnetic Field
In one experiment, they caused the nanoparticles to attach themselves specifically to the cell membrane of embryonic kidney cells. The membrane contains so-called capsaicin receptors (TRPV1), ion channels that are important for pain perception and numerous other functions. When a radio frequency magnetic field of approximately the strength used in magnetic resonance imaging was switched on, the nanoparticles reacted by heating up. This in turn activated the ion channels, leading to an influx of calcium and thus to a specific reaction of the cells.
Brain Cells Remotely Controlled
In a similar experiment, the researchers stimulated brain cells kept in culture by the nanoparticle-magnet method. Simply by switching on the magnetic field, they were able to trigger action potentials and thus nerve signals. The scientists controlled the fact that the nanoparticles actually just heated up during all of this by using a fluorescent agent coupled to them that began to glow when heated. “Our method is significant because it allows us to specifically heat only the cell membrane,” Pralle explains. “In doing so, there is no temperature change inside the cell.”
Nematode Changes Behavior “on Command”
In another experiment, the researchers wanted to test whether this manipulation is also possible on a living object, in this case the nematode Caenorhabditits elegans. To do this, they configured the nanoparticles so that they attached to sensory cells near the mouth part of the worm. When they turned on the external magnetic field, the nanoparticles heated up and triggered an avoidance response in the worm, as clearly seen in a video.
“You can see in the video that the worms initially crawl around normally. When we turn on the magnetic field, which heats the nanoparticles to 34 °C, most of the worms turn back,” Pralle explains. “We can use this method to direct them back and forth. Now we still need to figure out what other behaviors can be influenced in this way.”
Broad Application in Medicine Conceivable
However, the experiment on the nematodes not only demonstrates that the behavior of living organisms can be influenced using this method, it also shows that the nanoparticles can be positioned exactly where they are supposed to act, even on living objects. “By developing a method that allows us to use magnetic fields to stimulate cells in vitro and in vivo, this research can help decipher the signaling networks that control animal behavior,” Pralle said.
According to the researchers, the nanoparticles open up broad applications. In cancer therapy, they could be used to target proteins or cells in specific tissues for elimination. In diabetes treatment, they could stimulate pancreatic cells to produce more insulin. In neurological diseases caused by a lack of response from certain receptors in nerve cells, the nanoparticles could also stimulate them in a targeted manner.