Metal-free magnetic sensor can be safely implanted for wireless monitoring

October 27, 2026 feature Metal-free magnetic sensor can be safely implanted for wireless monitoring Sam Jarman Author Sadie Harley Scientific Editor Robert Egan Senior Editor Researchers in the U.S. and China have created a biocompatible, metal-free magnet that can be safely implanted and generate signals from deep inside the body. Led by Wubin Bai at the University of North Carolina, the team revealed how magnetism can emerge from the rearrangement of atoms in heated carbon nitride, which strengthens the coupling between unpaired electrons. Published in Nature Materials, their research could lead to new types of wireless sensors that provide valuable medical data, without any need for potentially harmful radiation. Implantable magnets Magnetic fields are ideally suited to medical monitoring. With their ability to penetrate deep into living tissue and track the real-time movements of organs wirelessly, techniques including MRI are now routinely used to create detailed medical images without subjecting the body to ionizing radiation. But as Bai explains, the approach has so far proven far less suitable for wearable or implantable sensors. "Conventional strong magnets usually contain metals that can corrode or remain in the body, while metal-free magnets have generally been too weak for reliable sensing through tissue," he says. In metals such as iron, magnetism arises when the magnetic moments of unpaired electrons are locked into a strong, long-range alignment. While this behavior can also emerge in metal-free compounds, the coupling between their unpaired electrons is generally far weaker. Ultimately, this means that the alignment is easily disrupted, leaving these materials only weakly magnetized once they are removed from an external magnetic field. Rearranged atomic structure Yet through their previous research, Bai's team uncovered an effect which appeared to upend this trend. When carbon nitride is heated to temperatures of several hundred degrees, they found that it produces a tiny amount of magnetically attracting residue. To investigate the effect, Bai's team studied the material using a combination of advanced analytical techniques. The observations revealed that the heating had removed some nitrogen atoms from the compound, leaving behind sites which could host unpaired electrons. At the same time, the reshaping of the compound's atomic layout introduced a new type of bonding structure, creating pathways that enabled these electrons to couple together. As a result, the alignment of their magnetic moments could persist even after the material was removed from an external magnetic field. Flowerlike patch Building on this discovery, Bai's team created their magnet from heat-treated graphitic carbon nitride: a semiconductor made from stacked 2D layers, best known for its use in absorbing visible light. "We combined this material with a biodegradable polymer and silk protein to make a soft patch that folds into a narrow delivery tube and opens like a flower on the cardiac surface," Bai describes. Once the patch is in place, an array of magnetic sensors worn on the skin can register the rising and falling magnetic signal produced as the patch is shifted by each heartbeat. Crucially, the signal is detected completely wirelessly, so the implant needs no battery or wired connection. When the team tested their system in pigs, it allowed them to calculate the proportion of blood pumped out of the heart's main pumping chamber with each heartbeat. Their estimates closely agreed with well-established ultrasound measurements. Over four weeks of continuous monitoring, the material proved compatible with the pigs' living tissues, before gradually breaking down into nontoxic molecules. Routes to medical sensing Altogether, their results show how a metal-free magnet can provide a medically viable signal from inside the body. While much more work will be needed before the technology can enter human trials, Bai's team is confident of its potential for medical monitoring. "This could eventually help doctors follow recovery after a heart attack or surgery more continuously, with a temporary implant that does not require a later operation for removal," Bai says. Written for you by our author Sam Jarman, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you. Publication details Yizhang Wu et al., Bioresorbable metal-free molecular magnets enable untethered organ monitoring, Nature Materials (2026). DOI: 10.1038/s41563-026-02759-4 Journal information: Nature Materials © 2026 Science X Network