Quantum spin resonance in engineered proteins for multimodal sensing

Scientists have engineered a class of magneto-sensitive fluorescent proteins, including MagLOV, that exhibit optically detected magnetic resonance in living bacterial cells at room temperature. The proteins were derived from the LOV2 domain and further modified through directed evolution to alter their responses to magnetic fields and radio frequencies. The effects arise from a spin-correlated radical-pair mechanism involving the protein backbone and a bound flavin cofactor. The resonance produces a signal-to-noise ratio high enough for single-cell detection on a standard wide-field fluorescence microscope. Both magnetic field effects and optically detected magnetic resonance signals can be measured through changes in fluorescence emission. The proteins can be expressed directly in host organisms and their performance adjusted through genetic methods such as rational design or directed evolution. Researchers applied gradient magnetic fields to localize the depth position of multiple bands of bacterial cells embedded in a three-dimensional volume. The magnetic field effects were attenuated by magnetic resonance imaging contrast agents in a dose-dependent manner consistent with spin relaxation. Variants with differing dynamic responses were generated to support signal multiplexing and lock-in detection in noisy measurement environments. The work shows that the proteins can serve as reporters for spatial imaging, microenvironment sensing, and mitigation of light scattering and autofluorescence in biological samples.