In doing so, they influence a sensitive quantum state known as spin and make it visible through light. In the future, these findings could help detect and even direct biochemical processes in cells simply from the outside using radio waves. Until now, quantum sensing was primarily understood from solid-state materials, such as diamonds, into which tiny defects were deliberately introduced. Researchers are now transferring this principle to proteins, biological molecules that can be genetically engineered and specifically tailored. In the future, this could allow for the direct integration of quantum sensors into cells or tissues.
These protein-based sensors are potentially particularly well-suited for biodetection, that is, for imaging living cells, tissues, or organs. In theory, they can be placed directly where the measurement is needed, making them ideal for studies in organisms, unlike bulky solid-state sensors.
Dominik Bucher, Professor of Quantum Sensing at TUM's Faculty of Natural Sciences and senior author of the study published in Nature Biotechnology, explains: "Unlike established solid-state-based systems, protein-based approaches can not only serve as sensors, but also open up the possibility of selectively controlling biological processes with radio waves – an extremely exciting prospect.
What exactly did the researchers do?
Researchers irradiated two light-sensitive proteins—called flavoproteins—with blue light. The starting point was a cryptochrome, a protein studied in biology as a potential sensor of magnetic fields in birds. The protein samples used in the study were provided by Professor Erik Schleicher's research group at the University of Freiburg. Light generates spin-correlated radical pairs and extraordinary spin properties in proteins: these are coupled electron pairs that are extremely sensitive to magnetic fields. This behavior can be made visible through the luminescence intensity of these proteins.
Next, the researchers deliberately applied radio waves and succeeded in altering the luminescence of the proteins—and thus the underlying radical pairs. This demonstrates that sensitive quantum states in the biological environment can be influenced by electromagnetic fields. The proteins act as sensors of magnetic fields and can even make the distributions of magnetic fields visible in the samples.
The signal is read purely optically using light, similar to solid-state quantum sensors. Although this is basic research, the findings have great potential for near-term biotechnological applications. Kun Meng, a PhD student at TUM's Faculty of Natural Sciences and first author of the study, explains: "The possibilities range from biological quantum sensors to radio-wave-controlled cellular activity, such as remote gene expression."
