For decades, a faint green glow from crystal jellyfish has illuminated the inner workings of life. The discovery of green fluorescent protein, or GFP, revolutionized biology, allowing scientists to track molecules inside living cells by making them light up under a laser. Now, researchers are giving these familiar tools a radical upgrade: harnessing their quantum properties to turn them into ultrasensitive sensors that could detect magnetic fields, neuronal firing and even early signs of disease.
At the heart of this effort is an idea that sounds like science fiction but rests on solid physics. “These fluorescent proteins that everybody uses as a fluorescent label can actually be turned into a qubit,” says Peter Maurer, a quantum engineer at the University of Chicago. Qubits are the fundamental units of quantum information, capable of existing in multiple states simultaneously. While quantum computers require qubits that are shielded from environmental disturbances, quantum sensors rely on qubits that are exquisitely sensitive to their surroundings.
Fluorescent proteins are already indispensable in biology labs worldwide. By attaching the gene for a glowing protein to a gene of interest, researchers can watch where proteins go, how they behave and how cells respond to drugs or stress. Variants have been engineered to respond to changes in pH, calcium levels or mechanical forces. But until recently, they could not directly sense magnetic fields—an ability that would dramatically expand their utility.
Quantum sensing, a rapidly advancing field, offers that possibility. Unlike traditional imaging techniques, quantum sensors can detect minute variations in magnetic and electric fields. Magnetic resonance imaging (MRI), for example, exploits the quantum property of spin in hydrogen nuclei to produce images of the body. Today’s leading quantum sensors often rely on defects in diamond crystals known as nitrogen-vacancy, or NV, centers. These tiny imperfections allow researchers to manipulate and read out electron spin states using lasers and microwaves, enabling measurements of magnetic fields, temperature and other environmental factors with extraordinary precision.
But diamonds are bulky compared with proteins and difficult to position precisely inside cells. Living systems are also, as physicist Ania Jayich of the University of California, Santa Barbara, puts it, “warm and messy.” That makes adapting NV-diamond technology for biological applications challenging. Fluorescent proteins, by contrast, are small and genetically targetable. Scientists can engineer cells to produce them exactly where needed—right next to a neuron’s firing site or a protein complex of interest.
The quantum revolution in proteins began when David Awschalom, director of the Chicago Quantum Institute, started exploring whether molecules could function as qubits. After demonstrating in 2020 that certain synthesized molecules could behave like qubits, his team turned its attention to biology. Partnering with Maurer, they focused on enhanced yellow fluorescent protein, or EYFP, a widely used laboratory staple.
Fluorescent proteins emit light when excited by a laser. Occasionally, their electrons enter a so-called triplet state—a metastable, non-fluorescent configuration with three possible spin orientations. Biologists have long considered this blinking behavior a nuisance because it dims the glow. For quantum engineers, however, the triplet state is a gift. It enables the creation of a coherent superposition of spins, the essential ingredient for quantum sensing.
Using lasers and microwaves, Awschalom and Maurer’s team succeeded in placing EYFP into the desired quantum state. Magnetic fields subtly altered the intensity of the emitted light—by about 30%—demonstrating that the protein could function as a quantum sensor. Remarkably, the system worked in living bacterial cells at room temperature, eliminating the need for extreme cooling that many quantum technologies require.
The implications are significant. Protein-based quantum sensors could detect the faint magnetic signatures of firing neurons or track tiny flows of ions within cells. They might identify trace amounts of free radicals that signal cellular stress or the early onset of cancer. Because the proteins are genetically encoded, researchers could deploy them with unprecedented precision, illuminating processes at the nanoscale.
There are hurdles to overcome. Fluorescent proteins are fragile and can degrade under prolonged illumination. Maurer’s group is working to engineer versions that spend more time in the triplet state, boosting sensitivity. Other teams are exploring whether these proteins can reliably detect changes in temperature or pH, as NV diamonds do.
Parallel efforts are under way elsewhere. At the Chan Zuckerberg Biohub in San Francisco, physicist Andrew York and collaborators discovered that certain red and green fluorescent proteins become magnetically sensitive when linked to a small organic molecule called a flavin. Engineer Harrison Steel at the University of Oxford has helped refine this system, creating thousands of protein variants and selecting the most responsive. These proteins exhibit distinct blinking patterns when exposed to magnetic fields and radio waves, raising the possibility of “multiplexing”—monitoring multiple targets simultaneously within the same tissue.
Steel’s group is also attempting to merge quantum sensing with imaging, effectively reinventing MRI on a microscopic scale. By applying magnetic-field gradients and radio waves, they aim to control when and where proteins flash, using the scattered light to reconstruct images from deeper within tissue. Early experiments have imaged fluorescent proteins embedded in mouse-sized plastic samples with half-millimeter resolution. Although still crude, the approach hints at a future in which researchers can peer deeper into living organisms without slicing them apart.
Beyond imaging, the technology could enable “magnetogenetics,” the remote activation of biological processes using magnetic fields. By switching proteins on or off at will, scientists might trigger therapeutic responses deep within the body. “That’s very exciting to think about,” says Nathan Shaner of the University of California, San Diego, who develops fluorescent proteins.
The field is young but advancing quickly. Funding initiatives in the United States and the United Kingdom are accelerating research into quantum sensing for biology. Some experts caution that fluorescent proteins must prove they can outperform established technologies such as NV diamonds. Others argue that their genetic targetability offers an unbeatable advantage.
For Maurer and his colleagues, the path forward is clear. They are not abandoning diamonds, but they believe proteins may ultimately dominate quantum sensing inside cells. As Jayich notes, what once seemed implausible now appears within reach. “This is just the beginning,” she says. “It’s not crazy. It’s really exciting.”
If successful, quantum proteins could transform biology as profoundly as GFP did decades ago—only this time, the glow would reveal not just where life happens, but the invisible forces that drive it.
