Cytosolic MagLOV Magnetofluorescence in Mammalian Cell Lines and Primary Neurons

Magnetic fields can influence the outcome of photochemical reactions through the radical pair mechanism, but whether this sensitivity extends to standard experimental conditions in mammalian cells has remained unclear. Here, we quantify the cytosolic magnetofluorescence of MagLOV, a genetically encoded, flavin-binding fluorescent protein, in mammalian cells, validated against extensive artifact controls. Excitation intensity and magnetic field strength differentially tune response kinetics and amplitude, respectively, with amplitude saturating above approximately 8 mT. Magnetic field-effect amplitude is further modulated by cellular culture state. This response generalizes across HEK293T, HeLa, U2OS, and A549 cells and primary mouse cortical neurons, with plateau amplitudes ranging from 1.4% to 2.7%. Together, these results establish that genetically encoded spin-dependent photochemistry can be quantitatively interrogated under standard mammalian live-cell imaging conditions, and generalizes across mammalian cell types.