Tiny sensor could guide needles through the body, monitor health from afar

Go for a biopsy these days and chances are your doctor will have to knock you out, slice part of you open, and fish around for the needed tissue. But what if a tiny sensor could guide a needle instead, mapping out your insides as it goes, all while you (and your doctor) watch on a video screen?

That's the promise of a new device, the size of a grain of sand, that can transmit a wireless signal up to 25 centimeters away. The work could also have implications for measuring blood pressure and tracking how medications metabolize inside the body, researchers say.

The device is "really exciting," says Nako Nakatsuka, a chemist who develops miniature biosensors to measure brain compounds at ETH Zürich and who was not involved with the study. The ability to maneuver inside the body with minimal disruption, she says, "is very cool."

The new sensor, whose workings are described today in Science, is made up of two magnets: One is fixed to a plastic casing, the other can twist and oscillate. An external device uses electromagnetic coils to create a magnetic field, which moves the second magnet. The device then gathers readings, such as temperature and pressure, by measuring changes in this second magnet.

"The design of the sensor is really smart and quite creative—it thinks outside the box," says Montserrat Calleja Gómez, a physicist who develops nanomechanical sensors at the Institute of Micro and Nanotechnology in Madrid who was not involved with the study.

The researchers then tested out their minisensor in a variety of settings. In one unusual experiment, they glued the tracker onto a bee's back. Even at the high speed that bees fly, the device was able to accurately track the insect's movements. "It was possible to track the path and the orientation [of bees in flight]," says co-author Jürgen Rahmer, a physicist at Philips Research. "It worked astonishingly well."

Rahmer's team also fitted a biopsy needle's tip with the sensor and injected it into a large, tissuelike gelatin blob to see whether the sensor could help guide medical instruments. The sensor accurately tracked the needle, and, by providing a map of where the needle was, enabled the scientists to navigate it to a target area (in this case, a dummy white ball within the blob). In the real world, the sensor could guide biopsy needles, catheters, and other instruments to the exact target to administer treatment, collect cell samples, or dissect a piece of tissue, the authors say.

If the sensor is swallowed, it could also monitor real-time changes inside the body, such as whether people with gastrointestinal issues are responding to medications or experiencing flare-ups, the team says.

The most exciting aspect though, Nakatsuka says, is the sensor's ability to measure pressure, which might one day allow doctors to detect blood pressure changes within blood vessels, potentially providing a more continuous way to monitor blood pressure, she says.

The distance that the detecting coils can be from the sensor is also a big advance, Calleja Gómez says. The researchers were able to detect a signal up to about 25 centimeters away, improving on previous wireless technologies that can only be up to 5 centimeters away, she points out. Expanding this distance could, for example, make it easier for patients to track their blood pressure at home, the authors say.

The device is also relatively cheap—costing anywhere from $1 to $100, depending on how long it needs to stay in the body—and how easy it is to manufacture, the authors say. "I can make it on the kitchen table," says study co-author Bernhard Gleich, a physicist at Philips. Besides the magnets, he says, "You just need a little bit plastic tubing, a little bit of string, and a little bit of adhesive and you put everything together."

Still, Gleich estimates that it might be 5 to 8 years before the device is used in humans for the simplest of applications. A lot of work is still needed to ensure that the sensors not only work properly, but also don't harm individuals.

Nakatsuka says trials would need to verify that the device doesn't provoke a negative reaction from the immune system or mess up normal blood flow. Still, she says, the possibilities are exciting. "I think it has the potential to go places we couldn't go before."