In vivo magnetic recording of neuronal action potentials using a differential TMR magnetrode

Neuronal magnetic signal recording intrinsically provides vector information and tissue transparency, offering a potential route to overcome the spatial resolution limitations of conventional electrophysiological recordings. However, in situ detection of neuronal magnetic signals at the cellular level remains highly challenging due to the limited sensitivity of microscale magnetic sensors and the presence of background noise. Here, we report a high-sensitivity implantable differential magnetrode based on a dual-pinned magnetic tunnel junction (TMR). By implementing a spatially decoupled differential architecture with a long baseline (5 mm), together with a sensitivity dynamically matched interface circuit, the device effectively suppresses environmental common-mode noise and achieves an ultralow detection limit of 68 pT/√Hz at 1 kHz. Benefiting from an optimized bidirectional SiO₂/Si₃N₄ protective interface, the device exhibits good biocompatibility and stability. Using this magnetrode, we detected action potential-related magnetic signals in the CA1 region of the rat hippocampus. Crucially, we experimentally observed polarity reversals in spike waveforms that correlate with neuronal spatial orientation, demonstrating the potential of magnetic recording to distinguish neural current directionality based on vector information. This work provides a novel sensing tool for microscale neuroscience research and offers a new technical pathway for resolving the spatial topology of complex neural circuits.