This student story was published as part of the 2026 NASW Perlman Virtual Mentoring Program organized by the NASW Education Committee, providing science journalism experience for undergraduate and graduate students.
Story by Nina Inman
Mentored and edited by Meredith Fore
Scientists have known for several years that a bird’s-eye view may involve more than just an elevated perspective. Birds and other animals are also sensitive to magnetic fields, but how they detect them remains an open question. In a study recently published in Nature, scientists have harnessed modern techniques in biology and experimental physics to understand this process.
An interdisciplinary group of scientists at Stanford University led by Professors Mark Kasevich, Steven Boxer, and Soichi Wakatsuki set out to characterize biological processes similar to magnetic sensing in birds using fluorescent proteins. The testbed for their research is a small organism called C. elegans, a species of nematode, genetically modified to have a synthetic fluorescent protein called mScarlet present in their cells. The strain of nematodes used was created using CRISPR-based gene editing technology.
In the study, the scientists controlled the level of fluorescence in a living organism by applying magnetic fields to gain insight into the biological process that causes fluorescence, including magnetic sensing in birds. Improved understanding of the process can create a pathway towards new biotechnologies involving magnetic fields.
Spin-correlated radical pairs: the thread connecting many biological systems
A hypothesis for how birds observe these fields lies in a quantum mechanical process called spin-correlated radical pairs, which is thought to be at the heart of a variety of biological processes from photosynthesis to biological magnetic sensing, such as that found in birds. In general, the number of electrons in a typical stable biological molecule is even, so every electron has a pair; but when a molecule has an unpaired electron, it becomes a radical. If radicals are created together, their electrons can become loosely intertwined, and the two molecules become spin-correlated radical pairs.
“What’s in doubt is whether this mechanism is what gives birds their magnetic field compass,” said Shaun Burd, a lead author of the work, on the broader impact of their findings. The study seeks to understand the mechanism of radical pairs, and a straightforward way to measure the dynamics of the process is using a fluorescent process involving mScarlet. The light emitted from the protein makes observation of dynamics feasible. While the fluorescent protein is not identical to the magnetic sensor in birds, the radical pair dynamics are translatable between these biological systems. At the molecular level, fluorescence in the protein system the Stanford group studied results from a chemical reaction between the fluorescent protein, mScarlet, and an additional molecule, flavin mononucleotide.
Once the molecules have formed into radical pairs, they can be in a variety of quantum states based on the configuration of their electrons. Depending on the state, the dynamics of the radical pairs is different, resulting in different levels of fluorescence. Researchers have no control over the configuration of the molecules following the creation of the radical pairs, but the story changes when magnetic fields are applied to the nematodes.
Based on the radical pair hypothesis, researchers expected that at low magnetic fields, there are many molecules in the fluorescing configuration, but as the field increases, the overall fluorescence of the system decreases due to modifications to the quantum state of the radical pairs from the field. Indeed, they found that as they increased the strength of the magnetic field on the sample, fluorescence decreased. This behavior is consistent with the proposed model for spin-correlated radical pairs in this system.
Controlling the radical pair dynamics
Researchers went one step further and applied an additional field to the sample to further control the radical pairs. They found that applying another magnetic field that oscillates in intensity over time at a special resonance frequency counteracted the effect of the initial magnetic field on the overall radical spin dynamics. Some of the lost fluorescence was recovered by the additional field, verifying that researchers modified the dynamics of the radical pair system.
By observing this phenomenon, the group showed that they can control a radical pair system in a complicated laboratory environment using a living animal. Beyond just understanding the biological process, researchers are interested in using these proteins in a variety of applications because they could have many advantages compared to other platforms, such as light or chemical-based biological technologies. Ph.D. student Nahal Bagheri, a lead author on the project, noted that this system is ripe for technological applications due to its robustness.
“A lot of people are looking for quantum sensing these days, but with biological systems, we avoid many of the problems with quantum sensors,” she commented. Further, biological tissues are essentially transparent to magnetic fields, which could make the proteins a valuable biomedical tool.
To move towards using proteins as tools, characterizing the protein’s response to magnetic fields is an essential step, and scientists have made the first step in controlling these processes in living things. Now Burd is beginning a group at Stanford to try to control biological processes beyond just fluorescence, such as neuron activity.
Main Header Image Caption: Graphic image of bird sensing magnetic field Credit: Phoenix Haupt at University of Arkansas (chaupt@uark.edu)
Nina Inman is a Ph.D. candidate at Rice University studying experimental AMO Physics. Nina does experiments on highly excited Rydberg atoms and she is interested in physics education.
The NASW Perlman Virtual Mentoring program is named for longtime science writer and past NASW President David Perlman. Dave, who died in 2020 at the age of 101 only three years after his retirement from the San Francisco Chronicle, was a mentor to countless members of the science writing community and always made time for kind and supportive words, especially for early career writers.
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